WO2013182713A1 - Improved heat-transfer fluids - Google Patents

Improved heat-transfer fluids Download PDF

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Publication number
WO2013182713A1
WO2013182713A1 PCT/ES2012/070414 ES2012070414W WO2013182713A1 WO 2013182713 A1 WO2013182713 A1 WO 2013182713A1 ES 2012070414 W ES2012070414 W ES 2012070414W WO 2013182713 A1 WO2013182713 A1 WO 2013182713A1
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Prior art keywords
fluid
thermal fluid
phase change
pcm
change material
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PCT/ES2012/070414
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Spanish (es)
French (fr)
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Marta HERNAIZ MIGUEL
Nerea URANGA ZUMETA
Estíbaliz ARANZABE BASTERRECHEA
Amaia MARTÍNEZ GOITANDIA
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Fundacion Tekniker
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Priority to PCT/ES2012/070414 priority Critical patent/WO2013182713A1/en
Publication of WO2013182713A1 publication Critical patent/WO2013182713A1/en

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
    • C09K5/08—Materials not undergoing a change of physical state when used
    • C09K5/10—Liquid materials

Definitions

  • the present invention relates to a new improved thermal fluid, by the ability to store heat, which comprises homogeneously dispersed or dissolved, an optionally encapsulated phase change material.
  • the invention also relates to the process for obtaining these fluids as well as their use in various applications such as in the solar thermal industry.
  • the eutectic diphenyl / diphenyl oxide mixture in a ratio of 26.5 / 73.5% by weight constitutes the heat transfer fluid (HTF) most used in the thermosolar industry, specifically in parabolic trough collector plants.
  • HTF heat transfer fluid
  • DP / DPO this mixture or fluid is marketed under the names THERMINOLVP1 and DOWTHERM A.
  • This fluid has certain properties that make it almost exclusive candidate for this application. Among the most outstanding properties is the wide range of application, between 20-400 e C, and its high stability and resistance to thermal degradation.
  • parabolic trough collector plants have had to adapt to meet the shortcomings that the fluid presents, such as its high vapor pressure, which means that the system must be pressurized to actually work in phase liquid
  • Another disadvantage of this fluid is its high freezing temperature, which is around 12 e C.
  • the temperature of the system varies and in case the temperature through which the HTF circulates becomes less than or close to 12 e C, the HTF freezes by blocking pipes, valves and other components.
  • the pipes are heated by electric tracing. Said tracing consists of electrical resistors along the pipes or around valves and pumps. In this way it is tried to minimize the risk of freezing of the fluid, but this implies an electrical consumption that negatively computes the performance of the plant.
  • phase change materials are known in the state of the art (PCM) which are currently used in heat exchange processes with thermal fluids or heat carriers (HTF).
  • PCM state of the art
  • HTF thermal fluids or heat carriers
  • These designs have the main disadvantage that in order to give such heat transfer, a heat exchanger has to be contemplated in the application, making the installation more complex and also reducing the performance of the reaction since the walls of the exchanger generate a thermal gradient , so that the final heat that reaches the fluid is always less than that which could reach it if there were direct and real contact between both systems. Also, being confined the specific area of the PCM is minimized.
  • the inventors of the present invention have surprisingly discovered that homogenization either by dispersion or by dissolving a phase change material (PMC) in a thermal fluid in a concentration range between 1 -30% converts the fluid into a new thermal fluid with improved properties in terms of its ability to store heat, at low temperature.
  • PMC phase change material
  • the PCMs are encapsulated in inorganic silicon structures by sol gel technology.
  • the microcapsules thus obtained have a size between 500 nm and 1 mre and are then homogeneously dispersed in the thermal fluid.
  • Figure 1 SEM image of encapsulated hexadecane, capsule size 500 nm
  • Figure 2 SEM image of encapsulated polyethylene glycol (PEG), capsule size 800 nm.
  • Fig. 3a It shows the result of an analysis with mastersizer 2000 in which it is observed that hexadecane is dispersed in a thermal fluid with a particle size distribution of 10 ⁇ .
  • Fig. 3b It shows that the PEG imidazolium chloride is dispersed with a particle size distribution of 5 ⁇ .
  • Fig. 3c It shows that encapsulated distearate PEG is dispersed with a particle size distribution greater than 10 ⁇ , probably due to particle aggregation.
  • Fig. 3d It shows that the encapsulated hexadecane is dispersed with a particle size distribution of 10 ⁇ .
  • Fig. 4 It shows the thermograms obtained under the DSC method, which reflect the behavior of the reference DP / DPO fluid and the fluid of the invention with 20% PEG distearate when subjected to TEST 2 (a thermal heating ramp of 25 e C to 400 e C at a speed of 10 e C / minute at a pressure of 2 MPa of nitrogen).
  • Fig. 5 It shows the thermograms obtained under the DSC method, which reflects the behavior of the DP / DPO reference fluid and that of the same sample of the fluid of the invention with 20% PEG distearate, when subjected to one and two tests consecutive TEST 1, and again to the TEST 1 test after a heating ramp of 25 to 400 e C at 10 e C / min and under 2 MPa of nitrogen (TEST 2) Fig. 6. Shows the thermograms that reflect the behavior of the fluid Reference DP / DPO when subjected to a dynamic DSC heating ramp from 25 e C to 400 e C at a speed of 10 e C / min and under 2MPas of nitrogen (TEST 2). Overlays are the curves under the same conditions (TEST 2) of the fluid of the invention with 20% PEG imidazolium chloride after two sweeps over the same sample.
  • the invention relates in one aspect to a new thermal fluid hereinafter fluid of the invention, comprising:
  • phase change material (ii) between 1 to 30% of a phase change material (PCM) with solid-liquid transition selected from the group consisting of organic, inorganic, ionic (non-hybrid) PCM, hybrid ionic liquids and mixtures thereof.
  • PCM phase change material
  • the thermal fluid useful for practicing the invention can be any conventional thermal fluid formulated on the basis of hydrorefined mineral oil or not, or on a synthetic basis such as silicones, esters, polyalphaolefins, glycols, aromatic organic oils, ionic liquids, or hybrids, or mixture of the above.
  • the PCMs useful for practicing the invention have a solid-liquid transition at a temperature close to the critical temperature of the thermal fluid, thereby understanding the minimum or maximum application temperature (that is, the working conditions). By next it is understood that it can be plus / minus 10% with respect to the critical temperature of the fluid. They are also chemically stable over the entire temperature range of application of the thermal fluid, that is, not decompose.
  • PCMs are conventional and therefore can be determined in each case by a person skilled in the art.
  • Organic PCMs include paraffinics and non-paraffinics;
  • Inorganic PCMs include metals and salts, and
  • ionic liquid PCMs include hybrids and non-hybrid, mono and dicationics.
  • the PCM is present in an amount 15-25% by weight, more preferably 20%.
  • paraffinic PCMs are, among others, aliens of between 14 and 34 carbon atoms such as hexadecane, octadecane, etc.
  • non-paraffinic PCM examples include, among others, formic acid, capric acid, lauric acid, benzoic acid, acetic acid, polyethylene glycol (PEG) of different molecular weights, 600, 1000, 10000, palmitic acid, stearic acid, and PEG distearate.
  • PEG polyethylene glycol
  • Illustrative examples of inorganic PCM are LiF, LiCI, LiBr, Lil, LiN0 3 , LiC0 3 , NaF, NaCI, NaBr, Nal, NaN0 3 , Na 2 C0 3 , KF, KCI, KBr, Kl, KN0 3 , KC0 3 , etc.
  • PCM of ionic liquids are structures constituted by an organic cation such as imidazolium, pyridinium, piperidinium with mono or di hydrocarbon substituents of different length, such as 1-benzyl-3-methylimidazolium, 1-butyl-1 - methylpyrrolidinium, N-propyl-N-methylpyrrolidine, 1-ethyl-3-methylimidazolium, among others; stabilized by inorganic anions such as halides, chloride, fluoride, or non-halides such as methyl sulfate (MeS04), bis (trifluorometillsulfonyl) imide [NTf2] among others.
  • organic cation such as imidazolium, pyridinium, piperidinium with mono or di hydrocarbon substituents of different length, such as 1-benzyl-3-methylimidazolium, 1-butyl-1 - methylpyrrolidinium, N-propyl-N-methylpyrrolidine
  • dicathionic structures can be formed whose molecular structure is constituted by two imidazolium or pyridinium cations, among others, linked by alkyl chains with a variable carbon number, such as 1, 7 bis (3-methylimidazolium-1 -yl bromide) ) heptane, 1, 8 bis (3-methylimidazolium-1 -yl) octane bromide, among others
  • hybrid ionic liquids are glycols, esters or complex hydrocarbon chains anchored to imidazolium, pyridinium, piperidinium cations, and stabilized with halides or not, such as, for example, polyethylene glycol 1-methylimidazolium,
  • the PCM is directly and homogeneously dispersed or dissolved within the thermal fluid.
  • the PCM is encapsulated in inorganic silicon structures and these are homogeneously dispersed within the thermal fluid. By encapsulation it is understood that the PCM is inside a shell (shell) hollow. Encapsulation of PCM with silicon is a conventional technique and there are documents in the state of the art known to a person skilled in the art who disclose its preparation. By homogeneously dispersed or dissolved, it is understood that there are no aggregates of PCM or encapsulated PCM that form a precipitate in the fluid.
  • the thermal fluid is the DP / DPO eutectic mixture that has a 26.5 / 73.5% weight ratio; It has a freezing temperature of 12 e C and a maximum working temperature of 400 e C.
  • Phase change materials are characterized by being chemical compounds that undergo a phase transition accumulate or release a large amount of energy in the form of latent heat (enthalpy), assuming a reversible heat storage and thus making the A system's temperature can be kept constant for long periods of time. They are also interesting materials for numerous applications because they also have other properties such as high thermal conductivity, chemical stability, low cost and are not corrosive or toxic.
  • PCM PCM
  • Non-paraffinic organic PCM PEG distearate
  • PCM hybrid ionic liquid PEG imidazolium chloride
  • Examples of particular embodiments according to the invention are the DP / DPO eutectic mixture with a PCM selected from the group consisting of: hexadecane, PEG distearate, PEG imidazolium chloride, encapsulated hexadecane and encapsulated distearate PEG.
  • a PCM selected from the group consisting of: hexadecane, PEG distearate, PEG imidazolium chloride, encapsulated hexadecane and encapsulated distearate PEG.
  • the fluid of the invention finds application in any installation or device that requires a thermal fluid or heat carrier.
  • the advantages of the fluid of the invention is that the PCM yields or evacuates heat, in which the fluid reaches a critical temperature, regardless of the point of the installation or device in which the fluid of the invention is located.
  • the thermal losses that nevertheless take place in the state of the art when the PCM and thermal fluid meet are minimized in differentiated tobacconists, and separated by a wall.
  • the final configuration of a system according to the invention is simplified since it is not necessary to include heat exchangers or a circuit that takes the fluid to the exchanger and returns it to the work area.
  • the invention in another aspect relates to a process for preparing the fluid of the invention.
  • the fluid of the invention is a homogeneous dispersion or solution of either PCM, or PCM encapsulated in inorganic silicon structures.
  • the preparation process hereinafter the process of the invention comprises the steps of:
  • Homogenization can be done with (a) mechanical means or (b) or sonic means.
  • homogenization by mechanical means is carried out with ultraturrax equipment.
  • This homogenization consists in stirring the thermal fluid with the PCM at different speeds. Typically this equipment works in the range of 3000 to 24000 rpm.
  • Homogenization by sonic means is also a conventional technique that involves the introduction of an ultrasound tip that works between 1 and 70 W.
  • the PCM is homogenized directly without encapsulating obtaining a dispersion or a solution depending on the nature of the fluid and the PCM.
  • the process of the invention comprises a step of encapsulating the PCM in a structure of silicon, and subsequently the resulting encapsulated PCM is homogenized in the thermal fluid as described above.
  • the additional advantage associated with the encapsulation of the PCM is that the PCM is protected against successive cycles of thermal stress to which the fluid of the invention is subjected. It also prevents the possible agglomeration of the PCM with each other that could lead to aggregates or that could solidify on the walls of the system that contains it.
  • the encapsulation can be carried out by the conventional sol gel procedure with a silicon precursor in a manner well known to a person skilled in the art. This sol gel procedure provides an inorganic silicon structure around each micro- or nanogota of PCM.
  • the sol gel encapsulation process comprises the following steps:
  • non-ionic surfactant such as polyoxyethylene 80 sorbitan monooleate (TWEEN 80) polyvinyl pyrrolidone (PVP), t-octylphenoxypolyethoxyethanol (Triton X-100), sorbitan laurate (SPAN20), dioctyl sodium sulfosuccinate , among others, at a concentration determined by its critical micellar concentration to generate an emulsion;
  • a non-ionic surfactant such as polyoxyethylene 80 sorbitan monooleate (TWEEN 80) polyvinyl pyrrolidone (PVP), t-octylphenoxypolyethoxyethanol (Triton X-100), sorbitan laurate (SPAN20), dioctyl sodium sulfosuccinate , among others, at a concentration determined by its critical micellar concentration to generate an emulsion;
  • TEOS tetraethyl orthosilicate
  • TMOS tetramethyl orthosilicate
  • silicon tetrachloride a catalyst
  • Dispersing a PCM encapsulated in the fluid could, a priori, decrease the thermal transfer of the PCM to the fluid, but in the case of the present invention, the capsules have an average micrometer diameter size, this is between 500 nm and 1 ⁇ , so that the surface area remains very high and the exchange very cash.
  • the experimentally determined sizes are illustrated in Figures 1 and 2 showing SEM images obtained with an optical microscope
  • the balance between the loss of encapsulating a PMC and the benefits that are achieved by minimizing the risk of aggregation of PCM or solidification at points of the installation may be favorable in some cases.
  • the experimental results of the Examples of the present invention show the effectiveness of homogenizing PCM in a thermal fluid to increase its resistance to lowering temperature. So it is possible to control the amount of PCM that is added to a fluid to preset the hours at which it can be at a certain critical temperature without freezing. Using between 1 and 30%, and preferably 20% of PCM, there is an improvement in fluid behavior in general, in the sense mentioned above, and in particular the DP / DPO at low temperature.
  • the PCM is the PEG imidazolium chloride which has shown that the thermal resistance it offers is very high.
  • low temperature is understood as a temperature close to (about ⁇ 10%) at the freezing point of a given fluid.
  • the invention relates to the use of the fluid of the invention as a thermal energy transport and storage system.
  • the fluid of the invention can therefore be used in any of the possible applications of a thermal fluid.
  • thermal applications that require fluids that transport thermal energy (heat or cold) from one point to another (domestic and industrial solar collectors, air conditioning systems, or in vehicles).
  • Conventional fluids have limited practical operating temperatures for various reasons, for example, because below a certain These temperatures can solidify producing a sealing of valves, pumps, causing significant damage to the installation that includes it as mentioned in the Background for example for the DP / DPO.
  • the fluids of the present invention allow to control the operating temperatures thereof thanks to the homogenization of the PCMs described.
  • the DP / DPO eutectic mixing fluid with PCM is used as described above, as a thermal energy transport and storage system, in particular in the solar thermal industry and more particularly in a parabolic trough collector plant.
  • the use of the fluid of the invention comprises the previous activation thereof to function as an energy transport and storage system, which comprises subjecting it to an elevated temperature that depends on each specific case according to the thermal fluid and the PCM. selected.
  • Example 1 Obtaining fluids according to the invention
  • PCM hexadecane, PEG distearate, PEG imidazolium chloride, encapsulated hexadecane and encapsulated PEG distearate at different concentrations (1%, 5%, 10%, 20%, 30%) in the DP / DPO fluid .
  • the following Table shows the homogenization conditions used for 20% of the indicated PCM. Mechanical homogenization was carried out in an ultraturrax device (IKA brand) and sonic homogenization in a SONOPLUS HD 2070 device (Bandelin).
  • the dispersions obtained were analyzed with the 2000 mastersizer (Malvern Instruments), which measures the particle size distribution between 0.01-3000 ⁇ . Both the dispersions obtained (in the case of hexadecane, PEG imidazolium chloride, encapsulated PEG distearate and encapsulated hexadecane) and the solutions obtained (in the case of distearate PEG) were monitored for 48 hours, observing that there was no aggregation or decantation or precipitation of compounds and thus demonstrating their homogeneity and stability.
  • 2000 mastersizer Malvern Instruments
  • PEG imidazolium chloride is dispersed with a particle size distribution of 5 ⁇ .
  • Encapsulated distearate PEG is dispersed with a particle size distribution greater than 10 ⁇ , probably due to particle aggregation.
  • the encapsulated hexadecane is dispersed with a particle size distribution of 10 ⁇ .
  • Example 2 Encapsulation by sol gel technique of hexadecane and PEG distearate
  • An emulsion was prepared by mixing 10 grams of each PCM with a non-ionic surfactant, (such as TWEEN 80, PVP, Triton X, SPAN20, AOT, among others), at a concentration determined by its critical micellar concentration. It was kept under stirring at 3000-24000 rpm for one hour and at a temperature of 25 e C.
  • a non-ionic surfactant such as TWEEN 80, PVP, Triton X, SPAN20, AOT, among others
  • this solution was added dropwise to the emulsion prepared above, left stirring for a time interval between 1 -12 hours at room temperature and 25 C. Finally the resulting capsules were washed with a solvent, alcohol , or water, and dried at a temperature not exceeding 200 e C.
  • the encapsulation produced silicon capsules (Si0 2 ) and hexadecane of size of 0.5 ⁇ (500 nm), and capsules of Si0 2 and PEG distearate of size 0.8 ⁇ (800 nm). In both cases the encapsulation percentage was 70% (percentage of PMC contained in each capsule).
  • the following table shows other results of PCM encapsulation such as temperatures and solid phase transition enthalpy - liquid of encapsulated and unencapsulated PCM, determined by DSC (Mettler Toledo) on a heating ramp of 0 e C a 100 e C with a heating rate of 10 e C / min, these tests were performed with a nitrogen flow rate of 50 ml / minute.
  • the behavior evaluation has been carried out with a fluid according to the invention comprising as thermal fluid: the DP / DPO eutectic mixture (reference fluid).
  • the technique used was Differential Scanning Calorimetry (DSC) (METTLER TOLEDO).
  • DSC Differential Scanning Calorimetry
  • the crucible crucible is a standard aluminum crucible of 100 microliters capacity and hermetically sealed lid.
  • the test method comprises the following stages: a) Isothermal stage at -50 e C for 10 min - to freeze the sample b) Dynamic ramp from -50 e C to 50 e C at a speed of 10 e C / min - to see the fusion of the fluid
  • the following table shows the freezing times (that is, the result of subjecting the fluids to the stages that constitute TEST 1, obtaining the freezing time of the isothermal stage d) of this TEST 1, for the reference thermal fluid ( DP / DPO) and two samples, sample 1 and sample 2, of the fluid of the invention with 20% PEG distearate measured 2 times each,
  • Figure 4 shows the behavior of the reference fluid and the fluid of the invention when subjected to the TEST 2 test.
  • the continuous line curve is the fluid of reference and it is observed that a fraction thereof evaporates at high temperatures, however the fluid of the invention represented in the dotted line curve maintains the baseline so it is thermally more stable, although there is a small loss of sample.
  • the analyzed fluid samples were again subjected to the test called TEST 1, to assess whether the PCM is still effective in the fluid of the invention and continues to delay its freezing compared to the fluid. reference.
  • Figure 5 shows the thermograms obtained under the DSC method consisting of the following stages (TEST 1): a) Isothermal stage at -50 e C for 10 min - to freeze the sample b) Dynamic ramp from -50 e C at 50 e C at a speed of 10 e C / min - to see the fusion of the fluid
  • thermogram shows the behavior of the reference fluid when subjected to the conditions of TEST 2 and superimposed on this curve are the curves under the same conditions of the fluid of the invention with 20% PEG imidazolium chloride after two sweeps on the same sample, observing that it is in the first scan where the reaction occurs and that it is irreversible since in the second scan performed to the same sample the peak is no longer observed exothermic at 240 e C.
  • the following table shows the results of freezing time of the reference fluid and of 3 samples of fluid of the invention, from DSC TEST 1) after activating the PEG imidazolium chloride.

Abstract

The invention relates to a novel heat-transfer fluid comprising (i) between 70 and 99 wt. % of a heat-transfer fluid; and between 1 and 30 wt. % of a phase-change material with a solid-liquid transition selected from the group formed by the organic, inorganic, (non-hybrid) ionic liquid, and hybrid ionic liquid phase-change materials, and the mixtures thereof. The invention also relates to a method for producing the novel heat-transfer fluid, comprising dispersing or dissolving the phase-change material encapsulated or otherwise by (a) mechanical homogenisation or (b) sonic homogenisation, and to the use of the novel fluid as a system for transporting heat energy, with an energy-storage capacity by combination of the latent heat emitted by the phase-change material in various applications.

Description

FLUIDOS TÉRMICOS MEJORADOS CAMPO DE LA INVENCIÓN  IMPROVED THERMAL FLUIDS FIELD OF THE INVENTION
La presente invención se refiere a un nuevo fluido térmico mejorado, por la capacidad de almacenar calor, que comprende homogéneamente disperso o disuelto, un material de cambio de fase opcionalmente encapsulado. La invención se refiere asimismo al procedimiento de obtención de estos fluidos así como a su utilización en diversas aplicaciones como por ejemplo en industria termosolar.  The present invention relates to a new improved thermal fluid, by the ability to store heat, which comprises homogeneously dispersed or dissolved, an optionally encapsulated phase change material. The invention also relates to the process for obtaining these fluids as well as their use in various applications such as in the solar thermal industry.
ANTECEDENTES DE LA INVENCIÓN BACKGROUND OF THE INVENTION
La mezcla eutéctica de difenil/óxido de difenilo en relación 26.5 / 73.5% en peso constituye el fluido caloportador (HTF) más empleado en la industria termosolar, concretamente en las plantas de colectores cilindro parabólicos. Genéricamente denominada DP/DPO, esta mezcla o fluido, es comercializada con los nombres THERMINOLVP1 y DOWTHERM A. Dicho fluido presenta ciertas propiedades que lo hacen candidato casi exclusivo para esta aplicación. Entre las propiedades más destacadas se encuentra el amplio rango de aplicación, entre 20-400eC, y su alta estabilidad y resistencia a la degradación térmica. A pesar de las buenas propiedades del fluido, las plantas de colectores cilindro parabólicos han tenido que adaptarse para suplir las carencias que el fluido presenta, como por ejemplo su alta presión de vapor, que supone que el sistema deba estar presurizado para trabajar realmente en fase líquida. Otra de las desventajas de este fluido es su alta temperatura de congelación, que se sitúa alrededor de los 12eC. En las plantas termosolares, debido a su modo de operación (que trabajan en ciclos con paradas y arranques) la temperatura del sistema varía y en caso de que la temperatura por donde circula el HTF llegue a ser inferior o cercana a los 12eC, el HTF congela obturando tuberías, válvulas y otros componentes. Con el fin de minimizar el riesgo de congelación del HTF en la planta se calorifugan las tuberías mediante traceado eléctrico. Dicho traceado consiste en resistencias eléctricas a lo largo de las tuberías o en torno a válvulas y bombas. De este modo se intenta minimizar el riesgo de congelación del fluido, pero ello supone un consumo eléctrico que computa negativamente al rendimiento de la planta. The eutectic diphenyl / diphenyl oxide mixture in a ratio of 26.5 / 73.5% by weight constitutes the heat transfer fluid (HTF) most used in the thermosolar industry, specifically in parabolic trough collector plants. Generically called DP / DPO, this mixture or fluid is marketed under the names THERMINOLVP1 and DOWTHERM A. This fluid has certain properties that make it almost exclusive candidate for this application. Among the most outstanding properties is the wide range of application, between 20-400 e C, and its high stability and resistance to thermal degradation. Despite the good properties of the fluid, parabolic trough collector plants have had to adapt to meet the shortcomings that the fluid presents, such as its high vapor pressure, which means that the system must be pressurized to actually work in phase liquid Another disadvantage of this fluid is its high freezing temperature, which is around 12 e C. In solar thermal plants, due to its mode of operation (working in cycles with stops and starts) the temperature of the system varies and in case the temperature through which the HTF circulates becomes less than or close to 12 e C, the HTF freezes by blocking pipes, valves and other components. In order to minimize the risk of freezing of HTF in the plant, the pipes are heated by electric tracing. Said tracing consists of electrical resistors along the pipes or around valves and pumps. In this way it is tried to minimize the risk of freezing of the fluid, but this implies an electrical consumption that negatively computes the performance of the plant.
Se conocen en el estado de la técnica diversos materiales de cambio de fase (PCM) los cuales se utilizan actualmente en procesos de intercambio de calor con fluidos térmicos o caloportadores (HTF). Las configuraciones conocidas hasta el momento donde el PCM cede el calor latente a un fluido, son a través de una pared por estar éste confinado en un recipiente estanco. Estos diseños, presentan la principal desventaja de que para darse dicha transferencia de calor, tiene que contemplarse en la aplicación un intercambiador de calor, haciendo más compleja la instalación y además disminuyendo el rendimiento de la reacción ya que las paredes del intercambiador generan un gradiente térmico, de modo que el calor final que le llega al fluido es siempre menor que el que le podría llegar si hubiera un contacto directo y real entre ambos sistemas. Así mismo al estar confinado el área específica del PCM se ve minimizada. Various phase change materials are known in the state of the art (PCM) which are currently used in heat exchange processes with thermal fluids or heat carriers (HTF). The configurations known until the moment where the PCM gives the latent heat to a fluid, are through a wall because it is confined in a sealed container. These designs have the main disadvantage that in order to give such heat transfer, a heat exchanger has to be contemplated in the application, making the installation more complex and also reducing the performance of the reaction since the walls of the exchanger generate a thermal gradient , so that the final heat that reaches the fluid is always less than that which could reach it if there were direct and real contact between both systems. Also, being confined the specific area of the PCM is minimized.
Existen otras configuraciones en donde hay un contacto directo entre el fluido y el PCM, que hacen referencia al empaquetamiento del PCM a modo de filtro por donde pasa el fluido y se produce la transferencia térmica, pero de nuevo hay una etapa de limpieza en la que se elimina el PCM del fluido para que éste esté limpio, La principal desventaja de esta configuración constituye el hecho de tener que limpiar el fluido de los restos de PCM para que el PCM siga actuando como filtro. Por tanto sigue existiendo en el estado de la técnica la necesidad de mejorar la transferencia de energía térmica entre un fluido y un PCM. There are other configurations where there is a direct contact between the fluid and the PCM, which refer to the packing of the PCM as a filter where the fluid passes and thermal transfer occurs, but again there is a cleaning stage in which The PCM is removed from the fluid so that it is clean. The main disadvantage of this configuration is the fact that the fluid has to be cleaned from the remains of PCM so that the PCM continues to act as a filter. Therefore, there is still a need in the state of the art to improve the transfer of thermal energy between a fluid and a PCM.
Asimismo existe la necesidad de minimizar el riesgo de congelación de un fluido térmico de forma alternativa a como se ha mencionado, de modo que se superen las desventajas expuestas. There is also a need to minimize the risk of freezing a thermal fluid in an alternative way as mentioned, so that the exposed disadvantages are overcome.
En este sentido los inventores de la presente invención han descubierto sorprendentemente que la homogeneización bien por dispersión o bien por disolución de un material de cambio de fase (PMC) en un fluido térmico en un rango de concentración entre 1 -30% convierte el fluido en un nuevo fluido térmico con propiedades mejoradas en cuanto a su capacidad de almacenar calor, a baja temperatura. In this sense, the inventors of the present invention have surprisingly discovered that homogenization either by dispersion or by dissolving a phase change material (PMC) in a thermal fluid in a concentration range between 1 -30% converts the fluid into a new thermal fluid with improved properties in terms of its ability to store heat, at low temperature.
Para evitar posibles problemas de adherencia de los PCM a las pareces de tuberías en las transiciones líquido/sólido, en una realización particular los PCM se encapsulan en estructuras inorgánicas de silicio mediante la tecnología sol gel. Las microcápsulas así obtenidas presentan un tamaño entre 500 nm y 1 miera y son a continuación dispersadas homogéneamente en el fluido térmico. To avoid possible problems of adhesion of the PCM to the pipes in liquid / solid transitions, in a particular embodiment the PCMs are encapsulated in inorganic silicon structures by sol gel technology. The microcapsules thus obtained have a size between 500 nm and 1 mre and are then homogeneously dispersed in the thermal fluid.
BREVE DESCRIPCIÓN DE LAS FIGURAS BRIEF DESCRIPTION OF THE FIGURES
Figura 1 : Imagen SEM de hexadecano encapsulado, tamaño de cápsula 500 nm Figura 2: Imagen SEM de polietilénglicol (PEG) diestearato encapsulado, tamaño de cápsula 800 nm.  Figure 1: SEM image of encapsulated hexadecane, capsule size 500 nm Figure 2: SEM image of encapsulated polyethylene glycol (PEG), capsule size 800 nm.
Fig. 3a. Muestra el resultado de un análisis con mastersizer 2000 en el que se observa que el hexadecano se dispersa en un fluido térmico con una distribución del tamaño de partícula de 10 μηι. Fig. 3a. It shows the result of an analysis with mastersizer 2000 in which it is observed that hexadecane is dispersed in a thermal fluid with a particle size distribution of 10 μηι.
Fig. 3b. Muestra que el PEG cloruro de imidazolio se dispersa con una distribución del tamaño de partícula de 5 μηι.  Fig. 3b. It shows that the PEG imidazolium chloride is dispersed with a particle size distribution of 5 μηι.
Fig. 3c. Muestra que el PEG diestearato encapsulado se dispersa con una distribución del tamaño de partícula mayor de 10 μηι seguramente por la agregación de partículas. Fig. 3c. It shows that encapsulated distearate PEG is dispersed with a particle size distribution greater than 10 μηι, probably due to particle aggregation.
Fig. 3d. Muestra que el hexadecano encapsulado se dispersa con una distribución del tamaño de partícula de 10 μηι.  Fig. 3d. It shows that the encapsulated hexadecane is dispersed with a particle size distribution of 10 μηι.
Fig. 4. Muestra los termogramas obtenidos bajo el método de DSC, que reflejan el comportamiento del fluido DP/DPO de referencia y del fluido de la invención con 20% de PEG diestearato al someterlos al TEST 2 (una rampa térmica de calentamiento de 25eC a 400eC a una velocidad de 10eC/minuto a presión de 2 MPa de nitrógeno). Fig. 4. It shows the thermograms obtained under the DSC method, which reflect the behavior of the reference DP / DPO fluid and the fluid of the invention with 20% PEG distearate when subjected to TEST 2 (a thermal heating ramp of 25 e C to 400 e C at a speed of 10 e C / minute at a pressure of 2 MPa of nitrogen).
Fig. 5. Muestra los termogramas obtenidos bajo el método de DSC, que refleja el comportamiento del fluido de referencia DP/DPO y el de una misma muestra del fluido de la invención con 20% de PEG diestearato, al someterlo a uno y a dos ensayos consecutivos TEST 1 , y nuevamente al ensayo TEST 1 tras una rampa de calentamiento de 25 a 400eC a 10eC/min y bajo 2 MPa de nitrógeno (TEST 2) Fig. 6. Muestra los termogramas que reflejan el comportamiento del fluido DP/DPO de referencia al someterlo a una rampa dinámica de calentamiento por DSC desde 25eC hasta 400eC a una velocidad de 10eC/min y bajo 2MPas de nitrógeno (TEST 2). Superpuestas están las curvas bajo las mismas condiciones (TEST 2) del fluido de la invención con 20% de PEG cloruro de imidazolio tras dos barridos sobre la misma muestra. Fig. 5. It shows the thermograms obtained under the DSC method, which reflects the behavior of the DP / DPO reference fluid and that of the same sample of the fluid of the invention with 20% PEG distearate, when subjected to one and two tests consecutive TEST 1, and again to the TEST 1 test after a heating ramp of 25 to 400 e C at 10 e C / min and under 2 MPa of nitrogen (TEST 2) Fig. 6. Shows the thermograms that reflect the behavior of the fluid Reference DP / DPO when subjected to a dynamic DSC heating ramp from 25 e C to 400 e C at a speed of 10 e C / min and under 2MPas of nitrogen (TEST 2). Overlays are the curves under the same conditions (TEST 2) of the fluid of the invention with 20% PEG imidazolium chloride after two sweeps over the same sample.
DESCRIPCIÓN DE LA INVENCIÓN DESCRIPTION OF THE INVENTION
La invención se refiere en un aspecto a un nuevo fluido térmico en adelante fluido de la invención, que comprende:  The invention relates in one aspect to a new thermal fluid hereinafter fluid of the invention, comprising:
(i) entre 70 y 99% de un fluido térmico; y (i) between 70 and 99% of a thermal fluid; Y
(ii) entre 1 a 30% de un material de cambio de fase (PCM) con transición sólido- líquido seleccionado del grupo formado por los PCM orgánicos, inorgánicos, líquidos iónicos (no híbridos), líquidos iónicos híbridos y sus mezclas.  (ii) between 1 to 30% of a phase change material (PCM) with solid-liquid transition selected from the group consisting of organic, inorganic, ionic (non-hybrid) PCM, hybrid ionic liquids and mixtures thereof.
Los porcentajes en la presente solicitud, a no ser que expresamente se diga de contrario, están expresados en peso respecto al peso total del fluido de la invención. The percentages in the present application, unless expressly stated otherwise, are expressed by weight with respect to the total weight of the fluid of the invention.
El fluido térmico útil para poner en práctica la invención puede ser cualquier fluido térmico convencional formulado en base a aceite mineral hidrorrefinado o no, o en base sintético como son por ejemplo las siliconas, ésteres, polialfaolefinas, glicoles, aceites orgánicos aromáticos, líquidos iónicos, o híbridos, o mezcla de los anteriores. The thermal fluid useful for practicing the invention can be any conventional thermal fluid formulated on the basis of hydrorefined mineral oil or not, or on a synthetic basis such as silicones, esters, polyalphaolefins, glycols, aromatic organic oils, ionic liquids, or hybrids, or mixture of the above.
Los PCM útiles para poner en práctica la invención presentan una transición sólido- líquido a una temperatura próxima a la temperatura crítica del fluido térmico entendiendo por tal la temperatura mínima o máxima de aplicación (es decir, de las condiciones de trabajo). Por próxima se entiende que la misma puede ser de más/menos 10% respecto a la temperatura crítica del fluido. Así mismo son químicamente estables en todo el rango de temperatura de aplicación del fluido térmico, es decir, no descomponerse. The PCMs useful for practicing the invention have a solid-liquid transition at a temperature close to the critical temperature of the thermal fluid, thereby understanding the minimum or maximum application temperature (that is, the working conditions). By next it is understood that it can be plus / minus 10% with respect to the critical temperature of the fluid. They are also chemically stable over the entire temperature range of application of the thermal fluid, that is, not decompose.
Los PCM son convencionales y por tanto pueden ser determinados en cada caso por un experto en la materia. Los PCM orgánicos incluyen los parafínicos y los no parafínicos; los PCM inorgánicos incluyen metales y sales, y los PCM líquidos iónicos, incluyen híbridos y sin hibridar, mono y dicatiónicos. En una realización preferente del fluido de la presente invención el PCM está presente en una cantidad del 15-25% en peso, más preferentemente en un 20%. PCMs are conventional and therefore can be determined in each case by a person skilled in the art. Organic PCMs include paraffinics and non-paraffinics; Inorganic PCMs include metals and salts, and ionic liquid PCMs include hybrids and non-hybrid, mono and dicationics. In a preferred embodiment of the fluid of the present invention the PCM is present in an amount 15-25% by weight, more preferably 20%.
Ejemplos de PCM parafínicos son, entre otros, aléanos de entre 14 y 34 átomos de carbono tales como el hexadecano, octadecano, etc. Examples of paraffinic PCMs are, among others, aliens of between 14 and 34 carbon atoms such as hexadecane, octadecane, etc.
Ejemplos de PCM no parafínicos son, entre otros, el ácido fórmico, el ácido cáprico, ácido láurico, ácido benzoico, ácido acético, polietilenglicol (PEG) de diferentes pesos moleculares, 600, 1000, 10000, ácido palmítico, ácido esteárico, y PEG diestearato. Examples of non-paraffinic PCM are, among others, formic acid, capric acid, lauric acid, benzoic acid, acetic acid, polyethylene glycol (PEG) of different molecular weights, 600, 1000, 10000, palmitic acid, stearic acid, and PEG distearate.
Ejemplos ilustrativos de PCM inorgánicos son LiF, LiCI, LiBr, Lil, LiN03, LiC03, NaF, NaCI, NaBr, Nal, NaN03, Na2C03, KF, KCI, KBr, Kl, KN03, KC03, etc. Illustrative examples of inorganic PCM are LiF, LiCI, LiBr, Lil, LiN0 3 , LiC0 3 , NaF, NaCI, NaBr, Nal, NaN0 3 , Na 2 C0 3 , KF, KCI, KBr, Kl, KN0 3 , KC0 3 , etc.
Ejemplos de PCM de líquidos iónicos (no híbridos) son estructuras constituidas por un catión orgánico como son imidazolio, piridinio, piperidinio con mono o di sustituyentes hidrocarbonados con diferente longitud, como son 1 -benzil-3- metilimidazolio, 1 -butil-1 -metilpirrolidinio, N-propil-N-metilpirrolidina, 1 -etil-3- metilimidazolio, entre otros; estabilizados por aniones inorgánicos como son los halógenuros, cloruro, fluoruro, o no halogenuros como el metilsulfato (MeS04), bis(trifluorometillsulfonil)imida [NTf2] entre otros. A su vez pueden estar formando estructuras dicatiónicas cuya estructura molecular está constituida por dos cationes imidazolio o piridinio, entre otros, unidas por cadenas alquílicas con un número de carbonos variable, como son bromuro de 1 ,7 bis(3-metilimidazolio-1 -yl)heptano, bromuro de 1 ,8 bis(3-metilimidazolio-1 -yl)octano, entre otros Examples of PCM of ionic liquids (non-hybrid) are structures constituted by an organic cation such as imidazolium, pyridinium, piperidinium with mono or di hydrocarbon substituents of different length, such as 1-benzyl-3-methylimidazolium, 1-butyl-1 - methylpyrrolidinium, N-propyl-N-methylpyrrolidine, 1-ethyl-3-methylimidazolium, among others; stabilized by inorganic anions such as halides, chloride, fluoride, or non-halides such as methyl sulfate (MeS04), bis (trifluorometillsulfonyl) imide [NTf2] among others. In turn, dicathionic structures can be formed whose molecular structure is constituted by two imidazolium or pyridinium cations, among others, linked by alkyl chains with a variable carbon number, such as 1, 7 bis (3-methylimidazolium-1 -yl bromide) ) heptane, 1, 8 bis (3-methylimidazolium-1 -yl) octane bromide, among others
Ejemplos de líquidos iónicos híbridos son glicoles, ásteres o cadenas hidrocarbonadas complejas ancladas a cationes imidazolio, piridinio, piperidinio, y estabilizadas con aniones halogenuros o no, como por ejemplo, el polietilenglicol 1 - metilimidazolio, Examples of hybrid ionic liquids are glycols, esters or complex hydrocarbon chains anchored to imidazolium, pyridinium, piperidinium cations, and stabilized with halides or not, such as, for example, polyethylene glycol 1-methylimidazolium,
hexafluorofosfato de PEG500 butilmetilimidazolio, bis(trifluorometilsulfonil)imida, de PEG10000 butilpiridinio , cloruro de PEG350metilimidazolio En una realización particular el PCM se encuentra directa y homogéneamente disperso o disuelto en el seno del fluido térmico. En otra realización particular el PCM se encuentra encapsulado en estructuras inorgánicas de silicio y éstas se encuentran homogéneamente dispersas en el seno del fluido térmico. Por encapsulado se entiende que el PCM se encuentra en el interior de una cáscara (shell) hueca. La encapsulación de PCM con silicio es una técnica convencional y existen documentos en el estado de la técnica conocidos para un experto en la materia que divulgan su preparación. Por homogéneamente disperso o disuelto se entiende que no hay agregados de PCM o de PCM encapsulado que formen un precipitado en el fluido. PEG500 butylmethylimidazolium hexafluorophosphate, bis (trifluoromethylsulfonyl) imide, PEG10000 butylpyridinium, PEG350methylimidazolium chloride In a particular embodiment the PCM is directly and homogeneously dispersed or dissolved within the thermal fluid. In another particular embodiment, the PCM is encapsulated in inorganic silicon structures and these are homogeneously dispersed within the thermal fluid. By encapsulation it is understood that the PCM is inside a shell (shell) hollow. Encapsulation of PCM with silicon is a conventional technique and there are documents in the state of the art known to a person skilled in the art who disclose its preparation. By homogeneously dispersed or dissolved, it is understood that there are no aggregates of PCM or encapsulated PCM that form a precipitate in the fluid.
En una realización preferente el fluido térmico es la mezcla eutéctica de DP/DPO que presenta una relación 26.5/73.5% en peso; presenta una temperatura de congelación de 12eC y una temperatura máxima de trabajo de 400eC. In a preferred embodiment the thermal fluid is the DP / DPO eutectic mixture that has a 26.5 / 73.5% weight ratio; It has a freezing temperature of 12 e C and a maximum working temperature of 400 e C.
Los materiales cambio de fase (PCM) se caracterizan por ser compuestos químicos que al sufrir una transición de fase acumulan o liberan gran cantidad de energía en forma de calor latente (entalpia), suponiendo un almacenamiento de calor reversible y haciendo de este modo que la temperatura de un sistema pueda mantenerse constante durante largos periodos de tiempo. Además son materiales interesantes para numerosas aplicaciones por presentar además otras propiedades como la alta conductividad térmica, estabilidad química, bajo coste y no son corrosivos ni tóxicos. Phase change materials (PCM) are characterized by being chemical compounds that undergo a phase transition accumulate or release a large amount of energy in the form of latent heat (enthalpy), assuming a reversible heat storage and thus making the A system's temperature can be kept constant for long periods of time. They are also interesting materials for numerous applications because they also have other properties such as high thermal conductivity, chemical stability, low cost and are not corrosive or toxic.
Ejemplos de PCM preferentes son: Examples of preferred PCM are:
PCM orgánico parafínico de 16 átomos de carbono (hexadecano),  Paraffinic organic PCM of 16 carbon atoms (hexadecane),
PCM orgánico no parafínico (PEG diestearato)  Non-paraffinic organic PCM (PEG distearate)
PCM líquido iónico híbrido (PEG cloruro de imidazolio).  PCM hybrid ionic liquid (PEG imidazolium chloride).
Ejemplos de realizaciones particulares según la invención son el DP/DPO mezcla eutéctica con un PCM seleccionado del grupo formado por: hexadecano, PEG diestearato, PEG cloruro de imidazolio, hexadecano encapsulado y el PEG diestearato encapsulado. Examples of particular embodiments according to the invention are the DP / DPO eutectic mixture with a PCM selected from the group consisting of: hexadecane, PEG distearate, PEG imidazolium chloride, encapsulated hexadecane and encapsulated distearate PEG.
El fluido de la invención encuentra aplicación en cualquier instalación o dispositivo que requiera un fluido térmico o caloportador. Las ventajas del fluido de la invención es que el PCM cede o evacúa calor, en el que el fluido alcanza una temperatura crítica, independientemente del punto de la instalación o dispositivo en la que se encuentre el fluido de la invención. En comparación con las configuraciones convencionales mencionadas en los Antecedentes, al encontrarse el PCM disperso o disuelto homogéneamente en el seno del fluido térmico, se minimizan las pérdidas térmicas que sin embargo tienen lugar en el estado de la técnica cuando el PCM y fluido térmico se encuentran en estancos diferenciados, y separados por una pared. La configuración final de un sistema según la invención se simplifica ya que no hay que incluir intercambiadores de calor ni un circuito que lleve el fluido hasta el intercambiador y lo devuelva a la zona de trabajo. The fluid of the invention finds application in any installation or device that requires a thermal fluid or heat carrier. The advantages of the fluid of the invention is that the PCM yields or evacuates heat, in which the fluid reaches a critical temperature, regardless of the point of the installation or device in which the fluid of the invention is located. In comparison with the conventional configurations mentioned in the Background, when the PCM is dispersed or dissolved homogeneously within the thermal fluid, the thermal losses that nevertheless take place in the state of the art when the PCM and thermal fluid meet are minimized in differentiated tobacconists, and separated by a wall. The final configuration of a system according to the invention is simplified since it is not necessary to include heat exchangers or a circuit that takes the fluid to the exchanger and returns it to the work area.
En otro aspecto la invención se relaciona con un procedimiento para la preparación del fluido de la invención. El fluido de la invención se trata de una dispersión o disolución homogénea bien de PCM, bien de PCM encapsulado en estructuras inorgánicas de silicio. El procedimiento de preparación, en adelante procedimiento de la invención comprende las etapas de: In another aspect the invention relates to a process for preparing the fluid of the invention. The fluid of the invention is a homogeneous dispersion or solution of either PCM, or PCM encapsulated in inorganic silicon structures. The preparation process, hereinafter the process of the invention comprises the steps of:
(i) poner en contacto el PCM con el fluido térmico, y  (i) contact the PCM with the thermal fluid, and
(ii) homogeneizar la mezcla resultante.  (ii) homogenize the resulting mixture.
La homogeneización puede hacerse con (a) medios mecánicos o (b) o medios sónicos. Homogenization can be done with (a) mechanical means or (b) or sonic means.
En una realización particular la homogeneización por medios mecánicos se lleva a cabo con un equipo ultraturrax. Esta homogeneización consiste en agitar el fluido térmico con el PCM a diferentes velocidades. Típicamente este equipo trabaja en el rango de entre 3000 a 24000 rpm. La homogeneización por medios sónicos es asimismo una técnica convencional que consiste en la introducción una punta de ultrasonidos que trabaja entre 1 y 70 W. In a particular embodiment, homogenization by mechanical means is carried out with ultraturrax equipment. This homogenization consists in stirring the thermal fluid with the PCM at different speeds. Typically this equipment works in the range of 3000 to 24000 rpm. Homogenization by sonic means is also a conventional technique that involves the introduction of an ultrasound tip that works between 1 and 70 W.
En una realización particular el PCM se homogeiniza directamente sin encapsular obteniéndose una dispersión o una disolución dependiendo de la naturaleza del fluido y del PCM. In a particular embodiment the PCM is homogenized directly without encapsulating obtaining a dispersion or a solution depending on the nature of the fluid and the PCM.
En otra realización particular antes de homogeneizar el PCM, el procedimiento de la invención comprende una etapa de encapsulacion del PCM en una estructura de silicio, y posteriormente el PCM resultante encapsulado se homogeiniza en el fluido térmico como se ha descrito anteriormente. In another particular embodiment before homogenizing the PCM, the process of the invention comprises a step of encapsulating the PCM in a structure of silicon, and subsequently the resulting encapsulated PCM is homogenized in the thermal fluid as described above.
La ventaja adicional asociada a la encapsulación del PCM reside en que se protege al PCM frente a sucesivos ciclos de estrés térmico al que se somete el fluido de la invención. Además impide la posible aglomeración del PCM entre sí que pudiera dar lugar a agregados o bien que pudiera solidificarse sobre las paredes del sistema que lo contiene. La encapsulación se puede llevar a cabo mediante el procedimiento convencional sol gel con un precursor de silicio de forma bien conocida para un experto en la materia. Este procedimiento sol gel proporciona una estructura inorgánica de silicio alrededor de cada micro- o nanogota de PCM. The additional advantage associated with the encapsulation of the PCM is that the PCM is protected against successive cycles of thermal stress to which the fluid of the invention is subjected. It also prevents the possible agglomeration of the PCM with each other that could lead to aggregates or that could solidify on the walls of the system that contains it. The encapsulation can be carried out by the conventional sol gel procedure with a silicon precursor in a manner well known to a person skilled in the art. This sol gel procedure provides an inorganic silicon structure around each micro- or nanogota of PCM.
En una realización particular el procedimiento de encapsulación sol gel comprende las siguientes etapas: In a particular embodiment, the sol gel encapsulation process comprises the following steps:
- mezclar el PCM y un surfactante no iónico, como son el monooleato de sorbitán polioxietilénico 80 (TWEEN 80) polivinilpirrolidona (PVP), t-octilfenoxipolietoxietanol (Tritón X-100), laurato de sorbitan (SPAN20), dioctil sodio sulfosuccinato (AOT), entre otros, en una concentración determinada por su concentración micelar crítica para generar una emulsión; - mixing the PCM and a non-ionic surfactant, such as polyoxyethylene 80 sorbitan monooleate (TWEEN 80) polyvinyl pyrrolidone (PVP), t-octylphenoxypolyethoxyethanol (Triton X-100), sorbitan laurate (SPAN20), dioctyl sodium sulfosuccinate , among others, at a concentration determined by its critical micellar concentration to generate an emulsion;
- mantener la emulsión resultante en agitación generalmente entre 3000-24000 rpm durante un tiempo determinado, generalmente de una hora, y a una temperatura comprendida entre 20-150eC; - maintaining the resulting emulsion generally between 3000 to 24,000 rpm agitation for a time, usually an hour, and at a temperature between 20-150 and C;
- hidrólisis de un precursor inorgánico de silicio, como son tetraetil ortosilicato (TEOS), tetrametil ortosilicato (TMOS), o tetracloruro de silicio entre otros, y por adición al mismo de la cantidad necesaria de agua y un catalizador (ácido o base); - hydrolysis of an inorganic silicon precursor, such as tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), or silicon tetrachloride among others, and by adding thereto the necessary amount of water and a catalyst (acid or base);
- adición de esta disolución que contiene el producto de hidrólisis gota a gota a la emulsión de PMC y surfactante no iónico; - adding this solution containing the hydrolysis product dropwise to the emulsion of PMC and non-ionic surfactant;
- mantener la mezcla resultante bajo agitación durante un intervalo de tiempo típicamente comprendido entre 1 -12 horas a temperatura comprendida entre 20- 150eC, - maintaining the resulting mixture under stirring for a time interval typically between 1 -12 hours at a temperature between 20- 150 and C,
- lavado de las cápsulas resultantes con un disolvente como alcohol o agua y secado a temperatura no superior a 200eC. - washing the resulting capsules with a solvent such as alcohol or water and drying at a temperature not exceeding 200 e C.
El hecho de dispersar un PCM encapsulado en el fluido, podría a priori disminuir la trasferencia térmica del PCM al fluido, pero en el caso de la presente invención, las cápsulas tienen un tamaño medio de diámetro micrométrico, esto es comprendido entre 500 nm y 1 μηι, por lo que el área superficial sigue siendo muy alta y el intercambio muy efectivo. Los tamaños determinados experimentalmente se ilustran en las Figuras 1 y 2 que muestran imágenes SEM obtenidas con microscopio ópticoDispersing a PCM encapsulated in the fluid could, a priori, decrease the thermal transfer of the PCM to the fluid, but in the case of the present invention, the capsules have an average micrometer diameter size, this is between 500 nm and 1 μηι, so that the surface area remains very high and the exchange very cash. The experimentally determined sizes are illustrated in Figures 1 and 2 showing SEM images obtained with an optical microscope
SEM modelo ULTRAplus (Zeiss). SEM ULTRAplus model (Zeiss).
El balance entre la perdida que se tiene al encapsular un PMC y los beneficios que se consiguen por minimizar el riesgo de agregación de PCM o solidificación en puntos de la instalación puede ser en algunos casos favorable. The balance between the loss of encapsulating a PMC and the benefits that are achieved by minimizing the risk of aggregation of PCM or solidification at points of the installation may be favorable in some cases.
Los resultados experimentales de los Ejemplos de la presente invención muestran la efectividad de homogeneizar PCM en un fluido térmico para aumentar la resistencia del mismo a bajar de temperatura. Por lo que es posible controlar la cantidad de PCM que se añade a un fluido para preestablecer las horas a las que éste puede estar a una determinada temperatura crítica sin llegar a congelarse. Empleando entre 1 y 30%, y preferiblemente un 20% de PCM, se constata una mejora en el comportamiento de fluidos en general, en el sentido arriba mencionado, y en particular del DP/DPO a baja temperatura. En una realización preferente el PCM es el PEG cloruro de imidazolio que ha mostrado que la resistencia térmica que ofrece es muy elevada. The experimental results of the Examples of the present invention show the effectiveness of homogenizing PCM in a thermal fluid to increase its resistance to lowering temperature. So it is possible to control the amount of PCM that is added to a fluid to preset the hours at which it can be at a certain critical temperature without freezing. Using between 1 and 30%, and preferably 20% of PCM, there is an improvement in fluid behavior in general, in the sense mentioned above, and in particular the DP / DPO at low temperature. In a preferred embodiment the PCM is the PEG imidazolium chloride which has shown that the thermal resistance it offers is very high.
En el contexto de la presente invención se entiende por baja temperatura una temperatura cercana (aproximadamente un ± 10%) a la del punto de congelación de un determinado fluido. In the context of the present invention, low temperature is understood as a temperature close to (about ± 10%) at the freezing point of a given fluid.
Por ello en otro aspecto la invención se refiere al uso del fluido de la invención como sistema de transporte y almacenamiento de energía térmica. El fluido de la invención puede por tanto emplearse en cualquiera de las posibles aplicaciones de un fluido térmico. En este sentido existen numerosas aplicaciones térmicas que requieren fluidos que transporten energía térmica (calor o frío) de un punto a otro (colectores solares domésticos e industriales, sistemas de aire acondicionado, o en vehículos). Los fluidos convencionales tienen limitadas sus temperaturas de operación prácticas por distintos motivos por ejemplo, porque por debajo de cierta temperatura éstos pueden solidificar produciendo una obturación de válvulas, bombas tuberías, causando daños importantes a la instalación que lo comprende como se ha comentado en los Antecedentes por ejemplo para el DP/DPO. Therefore, in another aspect the invention relates to the use of the fluid of the invention as a thermal energy transport and storage system. The fluid of the invention can therefore be used in any of the possible applications of a thermal fluid. In this sense there are numerous thermal applications that require fluids that transport thermal energy (heat or cold) from one point to another (domestic and industrial solar collectors, air conditioning systems, or in vehicles). Conventional fluids have limited practical operating temperatures for various reasons, for example, because below a certain These temperatures can solidify producing a sealing of valves, pumps, causing significant damage to the installation that includes it as mentioned in the Background for example for the DP / DPO.
Otra limitación en el empleo de fluidos convencionales deriva de la posible degradación del fluido por elevadas temperaturas y/o por presiones elevadas de vapor o porque determinados componentes puedan deteriorarse (degradación de componentes y rotura en el caso del estancamiento en colectores solares térmicos). Another limitation in the use of conventional fluids derives from the possible degradation of the fluid due to high temperatures and / or high vapor pressures or because certain components can deteriorate (degradation of components and breakage in the case of stagnation in thermal solar collectors).
Los fluidos de la presente invención permiten controlar las temperaturas de operación de los mismos gracias a la homogeneización de los PCM descritos. The fluids of the present invention allow to control the operating temperatures thereof thanks to the homogenization of the PCMs described.
En una realización particular se utiliza el fluido mezcla eutéctica DP/DPO con PCM según se ha descrito arriba, como sistema de transporte y almacenamiento de energía térmica, en particular, en la industria termosolar y más en particular en una planta de colectores cilindro parabólicos. In a particular embodiment, the DP / DPO eutectic mixing fluid with PCM is used as described above, as a thermal energy transport and storage system, in particular in the solar thermal industry and more particularly in a parabolic trough collector plant.
En otra realización particular el uso del fluido de la invención comprende la activación previa del mismo para que funcione como sistema de transporte y de almacenamiento de energía, que comprende someterlo a una temperatura elevada que depende de cada caso concreto según el fluido térmico y el PCM seleccionado.In another particular embodiment, the use of the fluid of the invention comprises the previous activation thereof to function as an energy transport and storage system, which comprises subjecting it to an elevated temperature that depends on each specific case according to the thermal fluid and the PCM. selected.
Así para un fluido DP/DPO con 20% en peso de PEG cloruro de imidazolio se ha visto que la activación es necesaria, y que ésta tiene lugar a la temperatura de activación de 240eC. A continuación se presentan ejemplos ilustrativos de la invención que se exponen para una mejor comprensión de la misma y en ningún caso deben considerarse una limitación del alcance de la misma. Thus, for a DP / DPO fluid with 20% by weight PEG imidazolium chloride it has been found that activation is necessary, and that this takes place at the activation temperature of 240 e C. Illustrative examples of the invention are presented below. that are exposed for a better understanding of it and in no case should be considered a limitation of its scope.
EJEMPLOS EXAMPLES
Ejemplo 1 : Obtención de fluidos según la invención Example 1: Obtaining fluids according to the invention
Se ha trabajado con los siguientes PCM: hexadecano, PEG diestearato, PEG cloruro de imidazolio, hexadecano encapsulado y el PEG diestearato encapsulado a diferentes concentraciones (1 %, 5%, 10%, 20%, 30%) en el fluido DP/DPO. En la siguiente Tabla se recogen las condiciones de homogeneización empleadas para un 20% de los PCM indicados. La homogeneización mecánica se llevó a cabo en un equipo ultraturrax (marca IKA) y la homogeneización sónica en un equipo SONOPLUS HD 2070 (Bandelin). We have worked with the following PCM: hexadecane, PEG distearate, PEG imidazolium chloride, encapsulated hexadecane and encapsulated PEG distearate at different concentrations (1%, 5%, 10%, 20%, 30%) in the DP / DPO fluid . The following Table shows the homogenization conditions used for 20% of the indicated PCM. Mechanical homogenization was carried out in an ultraturrax device (IKA brand) and sonic homogenization in a SONOPLUS HD 2070 device (Bandelin).
Figure imgf000012_0001
Figure imgf000012_0001
Las dispersiones obtenidas se analizaron con el mastersizer 2000 (Malvern Instruments), que mide la distribución del tamaño de partícula entre 0.01 -3000 μηι. Tanto las dispersiones obtenidas (en el caso del hexadecano, el PEG cloruro de imidazolio, PEG diestearato encapsulado y hexadecano encapsulado) como las disoluciones obtenidas (en el caso del PEG diestearato) fueron monitorizadas durante 48 horas observándose que no hubo agregación ni decantación ni precipitación de compuestos y demostrando por tanto la homogeneidad y estabilidad de las mismas. The dispersions obtained were analyzed with the 2000 mastersizer (Malvern Instruments), which measures the particle size distribution between 0.01-3000 μηι. Both the dispersions obtained (in the case of hexadecane, PEG imidazolium chloride, encapsulated PEG distearate and encapsulated hexadecane) and the solutions obtained (in the case of distearate PEG) were monitored for 48 hours, observing that there was no aggregation or decantation or precipitation of compounds and thus demonstrating their homogeneity and stability.
Los resultados experimentales de distribución de tamaño de partícula se muestran en las Figuras 3a a 3d y fueron los siguientes: -Hexadecano se dispersa con una distribución del tamaño de partícula de 10 μηι.The experimental results of particle size distribution are shown in Figures 3a to 3d and were as follows: -Hexadecano is dispersed with a particle size distribution of 10 μηι.
-El PEG cloruro de imidazolio se dispersa con una distribución del tamaño de partícula de 5 μηι. - El PEG diestearato encapsulado se dispersa con una distribución del tamaño de partícula mayor de 10 μηι seguramente por la agregación de partículas. -The PEG imidazolium chloride is dispersed with a particle size distribution of 5 μηι. - Encapsulated distearate PEG is dispersed with a particle size distribution greater than 10 μηι, probably due to particle aggregation.
- El hexadecano encapsulado se dispersa con una distribución del tamaño de partícula de 10 μηι.  - The encapsulated hexadecane is dispersed with a particle size distribution of 10 μηι.
Ejemplo 2: Encapsulación por técnica sol gel de hexadecano y de PEG diestearato Example 2: Encapsulation by sol gel technique of hexadecane and PEG distearate
Se preparó una emulsión mezclando 10 gramos de cada PCM con un surfactante no iónico, (como son el TWEEN 80, PVP, Tritón X, SPAN20, AOT, entre otros), en una concentración determinada por su concentración micelar crítica. Se mantuvo en agitación a 3000-24000 rpm durante una hora y a una temperatura de 25eC. An emulsion was prepared by mixing 10 grams of each PCM with a non-ionic surfactant, (such as TWEEN 80, PVP, Triton X, SPAN20, AOT, among others), at a concentration determined by its critical micellar concentration. It was kept under stirring at 3000-24000 rpm for one hour and at a temperature of 25 e C.
Por otra parte a 10 gr de un precursor inorgánico de silicio, (TEOS; TMOS, SiCI4, entre otros) se le añadió la cantidad necesaria de agua y de un catalizador (ácido o base) para llevar a cabo la hidrólisis. On the other hand, 10 g of an inorganic silicon precursor, (TEOS; TMOS, SiCI4, among others) was added the necessary amount of water and a catalyst (acid or base) to carry out the hydrolysis.
Una vez finalizada la hidrólisis, esta disolución se añadió gota a gota a la emulsión preparada anteriormente, dejándose en agitación durante un intervalo de tiempo entre 1 -12 horas a temperatura de 25eC. Finalmente las cápsulas resultantes se lavaron con un disolvente, alcohol o agua, y se secaron a temperatura no superior a 200eC. After the hydrolysis, this solution was added dropwise to the emulsion prepared above, left stirring for a time interval between 1 -12 hours at room temperature and 25 C. Finally the resulting capsules were washed with a solvent, alcohol , or water, and dried at a temperature not exceeding 200 e C.
La encapsulación produjo cápsulas de silicio (Si02) y hexadecano de tamaño de 0.5 μηι (500 nm), y cápsulas de Si02 y PEG diestearato de tamaño 0.8 μηι (800 nm). En ambos casos el porcentaje de encapsulación fue del 70% (porcentaje de PMC que contiene cada cápsula). En la siguiente tabla se muestran otros resultados de encapsulación de los PCM como son las temperaturas y entalpia de transición de fase sólido -líquido del PCM encapsulado y sin encapsular, determinadas por DSC (Mettler Toledo) en una rampa de calentamiento de 0eC a 100eC con una velocidad de calentamiento de 10eC/min, estos ensayos se realizaron con un caudal de nitrógeno de 50 ml/minuto. The encapsulation produced silicon capsules (Si0 2 ) and hexadecane of size of 0.5 μηι (500 nm), and capsules of Si0 2 and PEG distearate of size 0.8 μηι (800 nm). In both cases the encapsulation percentage was 70% (percentage of PMC contained in each capsule). The following table shows other results of PCM encapsulation such as temperatures and solid phase transition enthalpy - liquid of encapsulated and unencapsulated PCM, determined by DSC (Mettler Toledo) on a heating ramp of 0 e C a 100 e C with a heating rate of 10 e C / min, these tests were performed with a nitrogen flow rate of 50 ml / minute.
La reproducibilidad de los resultados pone de manifiesto que en el interior de la cápsula o cáscara hueca de silicio se encuentra el PCM T fusión ΔΗ Fusión ΔΗ cristalizaciónThe reproducibility of the results shows that inside the capsule or hollow silicon shell is the PCM T fusion ΔΗ Fusion ΔΗ crystallization
Muestra Tcristalización(eC) Tcristalization Sample ( e C)
(eC) (J/g)- (J/g)( e C) (J / g) - (J / g)
Hexadecano 17,30 15,47 161 159Hexadecane 17.30 15.47 161 159
Hexadecano Hexadecane
17,26 15,68 150 152 +SÍ02  17.26 15.68 150 152 + YES 02
PEG  PEG
16,12 19.24 79 80 DISTEARATO 16.12 19.24 79 80 DISTEARATE
SÍ02+ PEG YES 02 + PEG
16,26 19,54 88 83 DISTEARATO  16.26 19.54 88 83 DISTEARATE
Ejemplo 3: Evaluación del comportamiento del fluido de la invención Example 3: Evaluation of the behavior of the fluid of the invention
La evaluación del comportamiento se ha realizado con un fluido según la invención que comprende como fluido térmico: la mezcla eutéctica de DP/DPO (fluido de referencia). La técnica utilizada fue Calorimetría Diferencial de Barrido (DSC) (METTLER TOLEDO). El crisol empelado es un crisol estándar de aluminio de 100 microlitros de capacidad y con tapa sellada herméticamente.  The behavior evaluation has been carried out with a fluid according to the invention comprising as thermal fluid: the DP / DPO eutectic mixture (reference fluid). The technique used was Differential Scanning Calorimetry (DSC) (METTLER TOLEDO). The crucible crucible is a standard aluminum crucible of 100 microliters capacity and hermetically sealed lid.
Para ello se han diseñado unos tests específicos con los cuales se puede evaluar el tiempo que el fluido de la invención tarda en congelarse, su estabilidad, etc. For this purpose, specific tests have been designed with which the time that the fluid of the invention takes to freeze, its stability, etc. can be evaluated.
El método test al que se denomina TEST 1 , comprende las siguientes etapas: a) Etapa isotérmica a -50eC durante 10 min - para congelar la muestra b) Rampa dinámica desde -50eC a 50eC a una velocidad de 10eC/ min - para ver la fusión del fluido The test method, called TEST 1, comprises the following stages: a) Isothermal stage at -50 e C for 10 min - to freeze the sample b) Dynamic ramp from -50 e C to 50 e C at a speed of 10 e C / min - to see the fusion of the fluid
c) Rampa dinámica desde 50eC a -25eC a velocidad de 10eC/min d) Etapa isotérmica a -25eC durante 240 minutos - monitorizar el tiempo de congelación. Para poder establecer un estudio comparativo se evalúa igualmente el fluido térmico de referencia, sin PCM, y se miden varias muestras (alícuotas) de cada una de las dispersiones obtenidas (fluido de la invención) con cada PCM, para evaluar tanto la reproducibilidad del método como para verificar que se tiene una dispersión o una disolución homogénea. c) Dynamic ramp from 50 e C to -25 e C at a speed of 10 e C / min d) Isothermal stage at -25 e C for 240 minutes - monitor freezing time. In order to establish a comparative study, the reference thermal fluid is also evaluated, without PCM, and several samples (aliquots) of each of the dispersions obtained (fluid of the invention) are measured with each PCM, to evaluate both the reproducibility of the method as to verify that there is a dispersion or a homogeneous solution.
La siguiente tabla muestra los tiempos de congelación (es decir, el resultado de someter los fluidos a las etapas que constituyen el TEST 1 , obteniéndose el tiempo de congelación de la etapa isotérmica d) de este TEST 1 , para el fluido térmico de referencia (DP/DPO) y dos muestras, muestra 1 y muestra 2, del fluido de la invención con 20% de PEG diestearato medidas 2 veces cada una, The following table shows the freezing times (that is, the result of subjecting the fluids to the stages that constitute TEST 1, obtaining the freezing time of the isothermal stage d) of this TEST 1, for the reference thermal fluid ( DP / DPO) and two samples, sample 1 and sample 2, of the fluid of the invention with 20% PEG distearate measured 2 times each,
Figure imgf000015_0001
Figure imgf000015_0001
Se observa que la dispersión de un 20% de PEG diestearato retrasa la congelación del fluido en más de treinta minutos. Las muestras (alícuotas) analizadas 2 veces indican que los resultados son reproducibles, y que el fluido de la invención es homogéneo y estable. It is observed that the dispersion of 20% PEG distearate delays the freezing of the fluid in more than thirty minutes. The samples (aliquots) analyzed twice indicate that the results are reproducible, and that the fluid of the invention is homogeneous and stable.
Para evaluar la estabilidad del fluido de la invención y compararla con la del DP/DPO de referencia se han sometido muestras a condiciones típicas de operación de este tipo de fluidos caloportadores. Para simular estas condiciones de trabajo, las muestras se sometieron a un test dinámico, denominado TEST 2, con el DSC, que consiste en una rampa térmica de 25eC hasta 400eC a una velocidad de 10eC/minuto y bajo 2 MPa (20 bares) de presión de nitrógeno. To evaluate the stability of the fluid of the invention and compare it with that of the reference DP / DPO, samples have been subjected to typical operating conditions of this type of heat transfer fluid. To simulate these working conditions, the samples were subjected to a dynamic test, called TEST 2, with the DSC, which consists of a thermal ramp from 25 e C to 400 e C at a speed of 10 e C / minute and under 2 MPa (20 bar) nitrogen pressure.
La Figura 4 muestra el comportamiento del fluido de referencia y del fluido de la invención al someterlos al ensayo TEST 2. La curva en línea continua es el fluido de referencia y se observa que una fracción del mismo se evapora a altas temperaturas, sin embargo el fluido de la invención representado en la curva con línea punteada mantiene la línea base por lo que es térmicamente más estable, aunque sí que hay una pequeña perdida de muestra. Figure 4 shows the behavior of the reference fluid and the fluid of the invention when subjected to the TEST 2 test. The continuous line curve is the fluid of reference and it is observed that a fraction thereof evaporates at high temperatures, however the fluid of the invention represented in the dotted line curve maintains the baseline so it is thermally more stable, although there is a small loss of sample.
Después de someter los fluidos al ensayo TEST 2, las muestras de fluido analizadas se sometieron de nuevo al ensayo denominado TEST 1 , para evaluar si el PCM sigue siendo efectivo en el fluido de la invención y sigue retrasando la congelación del mismo en comparación al fluido de referencia. After submitting the fluids to the TEST 2 test, the analyzed fluid samples were again subjected to the test called TEST 1, to assess whether the PCM is still effective in the fluid of the invention and continues to delay its freezing compared to the fluid. reference.
Las muestras 1 y 2 se sometieron a dicho TEST 1 y se monitorizo el tiempo de congelación dado por la etapa isotérmica d) a -25eC durante 240 minutos. Se obtuvieron los resultados de la siguiente tabla: Samples 1 and 2 were subjected to said TEST 1 and the freezing time given by isothermal step d) at -25 e C was monitored for 240 minutes. The results of the following table were obtained:
Figure imgf000016_0001
Figure imgf000016_0001
Se demuestra que el PCM sigue siendo efectivo y sigue retrasando la congelación del fluido de la invención. El ensayo también pone de manifiesto que se produce una pérdida de muestra cuando se somete a un ciclo de alta temperatura (TEST 2), pero menor que la que se produce del fluido de referencia DP/DPO. It is shown that the PCM remains effective and continues to delay the freezing of the fluid of the invention. The test also shows that a sample loss occurs when subjected to a high temperature cycle (TEST 2), but less than that produced from the DP / DPO reference fluid.
En la Figura 5 se muestran los termogramas obtenidos bajo el método de DSC constituido por las siguientes etapas (TEST 1 ): a) Etapa isotérmica a -50eC durante 10 min - para congelar la muestra b) Rampa dinámica desde -50eC a 50eC a una velocidad de 10eC/ min - para ver la fusión del fluido Figure 5 shows the thermograms obtained under the DSC method consisting of the following stages (TEST 1): a) Isothermal stage at -50 e C for 10 min - to freeze the sample b) Dynamic ramp from -50 e C at 50 e C at a speed of 10 e C / min - to see the fusion of the fluid
c) Rampa dinámica desde 50eC a -25eC a velocidad de 10eC/min c) Dynamic ramp from 50 e C to -25 e C at a speed of 10 e C / min
d) Etapa isotérmica a -25eC durante 240 minutos - monitorizar el tiempo de congelación. Los resultados reflejan el comportamiento del fluido de referencia DP/DPO y el de una misma muestra del fluido de la invención con 20% de PEG diestearato, al someterlo a uno y a dos ensayos TEST 1 consecutivos, a una rampa de calentamiento de 25 a 400eC a 10eC/min bajo 2 MPa de nitrógeno (TEST 2), y nuevamente a un ensayo TEST 1 . d) Isothermal stage at -25 e C for 240 minutes - monitor freezing time. The results reflect the behavior of the DP / DPO reference fluid and that of the same sample of the fluid of the invention with 20% PEG distearate, when subjected to one and two consecutive TEST 1 tests, to a heating ramp of 25 to 400 e C at 10 e C / min under 2 MPa of nitrogen (TEST 2), and again to a TEST 1 test.
El mismo estudio se ha realizado para el fluido de la invención con 20% en peso de PEG cloruro de imidazolio en DP/DPO. The same study was carried out for the fluid of the invention with 20% by weight of PEG imidazolium chloride in DP / DPO.
Resultados después de someter el fluido de la invención y el de referencia a la etapa d) del TEST 1 para evaluar el tiempo de congelación: Results after submitting the fluid of the invention and the reference to step d) of TEST 1 to evaluate the freezing time:
Figure imgf000017_0001
En este caso sorprendentemente los inventores han observado que este PCM en esta concentración, aparentemente no es efectivo.
Figure imgf000017_0001
In this case, surprisingly, the inventors have observed that this PCM at this concentration is apparently not effective.
Las muestras se sometieron entonces a la rampa térmica según el TEST 2 y lo que se observó en el fluido de la invención es que a 240eC hay un pico exotérmico, que se asocia con una reacción entre el PCM y el DP/DPO. The samples were then subjected to the thermal ramp according to TEST 2 and what was observed in the fluid of the invention is that at 240 e C there is an exothermic peak, which is associated with a reaction between the PCM and the DP / DPO.
El termograma (ver Figura 6) muestra el comportamiento del fluido de referencia al someterlo a las condiciones del TEST 2 y superpuestas a esta curva están las curvas bajo las mismas condiciones del fluido de la invención con 20% de PEG cloruro de imidazolio tras dos barridos sobre la misma muestra, observándose que es en el primer barrido donde se da la reacción y que es irreversible puesto que en el segundo barrido realizado a la misma muestra ya no se observa el pico exotérmico a 240eC. The thermogram (see Figure 6) shows the behavior of the reference fluid when subjected to the conditions of TEST 2 and superimposed on this curve are the curves under the same conditions of the fluid of the invention with 20% PEG imidazolium chloride after two sweeps on the same sample, observing that it is in the first scan where the reaction occurs and that it is irreversible since in the second scan performed to the same sample the peak is no longer observed exothermic at 240 e C.
Las muestras (alícuotas) tras ser sometidas a la rampa térmica TEST 2 se someten al ensayo TEST 1 para evaluarlas. Se observó sorprendentemente que el PCM es después activo y retrasa la congelación del fluido de la invención respecto al fluido de referencia, por lo que se pone de manifiesto la necesidad de una etapa de activación previa a temperatura de 240eC para que este fluido de la invención presente el comportamiento mejorado. The samples (aliquots) after being subjected to the TEST 2 thermal ramp are subjected to the TEST 1 test to evaluate them. It was surprisingly observed that the PCM is then active and delays the freezing of the fluid of the invention with respect to the reference fluid, whereby the need for a previous activation stage at a temperature of 240 e C is revealed for this fluid to The invention exhibits improved behavior.
Estos resultados indican que para que determinados fluidos térmicos según la invención sean eficaces, es necesario llevar a cabo una etapa previa de activación, lo cual puede ser determinado fácilmente por un experto en la materia. These results indicate that in order for certain thermal fluids according to the invention to be effective, it is necessary to carry out a previous activation stage, which can easily be determined by one skilled in the art.
La siguiente tabla muestra los resultados de tiempo de congelación del fluido de referencia y de 3 muestras de fluido de la invención, de DSC TEST 1 ) tras activar el PEG cloruro de imidazolio. The following table shows the results of freezing time of the reference fluid and of 3 samples of fluid of the invention, from DSC TEST 1) after activating the PEG imidazolium chloride.
Figure imgf000018_0001
Figure imgf000018_0001
En conclusión para el PEG cloruro de imidazolio se observa que necesita de una activación a 240eC para empezar a ser efectivo. Además se observa que las dispersiones obtenidas con este PCM no se degradan al someterlas a condiciones típicas de operación de fluidos caloportadores y que el tiempo de retraso de la congelación es mayor a 4 horas. In conclusion for the PEG imidazolium chloride it is observed that it needs an activation at 240 e C to start being effective. Furthermore, it is observed that the dispersions obtained with this PCM do not degrade when subjected to typical operating conditions of heat transfer fluids and that the freezing delay time is greater than 4 hours.

Claims

REIVINDICACIONES
1 . Nuevo fluido térmico que comprende: 1 . New thermal fluid that includes:
(iii) entre 70 y 99% de un fluido térmico; y (iii) between 70 and 99% of a thermal fluid; and
(iv) entre 1 a 30% de un material de cambio de fase seleccionado del grupo formado por los materiales de cambio de fase orgánicos, inorgánicos, líquidos iónicos, líquidos iónicos híbridos y sus mezclas. (iv) between 1 to 30% of a phase change material selected from the group consisting of organic, inorganic phase change materials, ionic liquids, hybrid ionic liquids and their mixtures.
2. Nuevo fluido térmico según la reivindicación 1 en el que el fluido térmico se selecciona del grupo formado por fluidos térmicos formulados en base a aceite mineral hidrorrefinado y no hidrorrefinado, formulados en base sintético y sus mezclas. 2. New thermal fluid according to claim 1 wherein the thermal fluid is selected from the group formed by thermal fluids formulated based on hydrorefined and non-hydrorefined mineral oil, formulated on a synthetic basis and their mixtures.
3. Nuevo fluido térmico según la reivindicación 1 o 2 donde el material de cambio de fase se selecciona del grupo formado por los materiales de cambio de fase orgánicos parafínicos y no parafínicos, los materiales inorgánicos sales y metales, y los materiales líquidos iónicos híbridos y sin hibridar, mono y dicatiónicos, y sus mezclas. 3. New thermal fluid according to claim 1 or 2 wherein the phase change material is selected from the group formed by paraffinic and non-paraffinic organic phase change materials, inorganic materials salts and metals, and hybrid ionic liquid materials and unhybridized, mono- and dicationic, and their mixtures.
4. Nuevo fluido térmico según la reivindicación 3, en el que el material de cambio de fase está presente en una cantidad comprendida entre 15 y 25% en peso, preferiblemente en un 20% en peso. 4. New thermal fluid according to claim 3, wherein the phase change material is present in an amount between 15 and 25% by weight, preferably 20% by weight.
5. Nuevo fluido térmico según la reivindicación 3 o 4, en el que el material de cambio de fase se encuentra homogéneamente disperso o disuelto en el fluido térmico. 5. New thermal fluid according to claim 3 or 4, wherein the phase change material is homogeneously dispersed or dissolved in the thermal fluid.
6 Nuevo fluido térmico según una cualquiera de las reivindicaciones 3 a 5, en el que el material de cambio de fase se encuentra encapsulado en estructuras inorgánicas de silicio y estas cápsulas presentan un tamaño comprendido entre 500 nm y 1 μηι y se encuentran homogéneamente dispersas en el fluido térmico. 6 New thermal fluid according to any one of claims 3 to 5, wherein the phase change material is encapsulated in inorganic silicon structures and these capsules have a size between 500 nm and 1 μηι and are homogeneously dispersed in the thermal fluid.
7. Nuevo fluido térmico según una cualquiera de las reivindicaciones anteriores en el que el fluido térmico es la mezcla eutéctica de DP/DPO que presenta una relación 26.5/73.5% en peso. 7. New thermal fluid according to any one of the previous claims in in which the thermal fluid is the eutectic mixture of DP/DPO that has a ratio of 26.5/73.5% by weight.
8. Procedimiento para la preparación del nuevo fluido térmico según una cualquiera de las reivindicaciones anteriores que comprende las etapas de: 8. Procedure for the preparation of the new thermal fluid according to any one of the preceding claims, comprising the steps of:
(iii) poner en contacto el material de cambio de fase con el fluido térmico, y (iii) contact the phase change material with the thermal fluid, and
(iv) homogeneizar. (iv) homogenize.
9. Procedimiento según la reivindicación 8, que comprende además la encapsulacion del material de cambio de fase con una estructura inorgánica de silicio mediante la técnica sol gel. 9. Method according to claim 8, further comprising encapsulating the phase change material with an inorganic silicon structure using the sol gel technique.
10. Uso del fluido según una cualquiera de las reivindicaciones 1 a 7, como sistema de transporte y almacenamiento de energía térmica. 10. Use of the fluid according to any one of claims 1 to 7, as a thermal energy transport and storage system.
1 1 . Uso según la reivindicación 10 en el que el fluido térmico es la mezcla eutéctica DP/DPO. eleven . Use according to claim 10 wherein the thermal fluid is the DP/DPO eutectic mixture.
12. Uso según la reivindicación 10 u 1 1 en una planta de colectores cilindro parabólicos. 12. Use according to claim 10 or 1 1 in a parabolic trough plant.
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