US 3739487 A
A drying apparatus comprising a cabinet for housing articles to be dried and an air conditioning plant including air cooling means to condense water from water vapor-laden air drawn in from the cabinet by a circulating fan and means to heat the air recycled back into the cabinet, the air cooling means and air heating means being the evaporator and condenser respectively of a refrigeration plant, a metered part of the circulating air only being passed over the evaporator by a second fan and part of the heat produced by the condenser being lost externally to the apparatus.
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Description (OCR text may contain errors)
United States Patent 1 Clark 4] DRYING APPARATUS  Inventor: Ronald John Clark, 17 Bream Down Avenue, Weston-Super-Mare, England  Filed: May 25, 1971  Appl. No.: 146,666
3 1943 Phipps 34/77 June 19, 1973 2,643,523 6/1953 Burgess 34/77 2,627,699 2/1953 Candor.... 34/76 3,270,530 9/1966 Czech 134/77  ABSTRACT A drying apparatus comprising a cabinet for housing articles to be dried and an air conditioning plant including air cooling means to condense water from water vapor-laden air drawn in from the cabinet by a circulating fan and means to heat the air recycled back into the cabinet, the air cooling means and air heating means being the evaporator and condenser respectively of a refrigeration plant, a metered part of the circulating air only being passed over the evaporator by a second fan and part of the heat produced by the condenser being lost externally to the apparatus.
7 Claims, 8 Drawing Figures PAIENIED JUN 1 9191s sum 2 or e USU 5N7 R NALD .J. Chm/e DRYING APPARATUS BACKGROUND OF THE INVENTION 1. This invention relates to improvements in drying apparatus, particularly for the removal of water from domestic articles such as clothing, and comprises an air conditioning part arranged to work in conjunction with acabinet o'r closet, which may include racks for supporting wet articles. The air conditioning part includes .an air cooling means and an air heating means formed by the evaporator and condenser respectively of a refrigeration machine, the evaporator serving to cool air passing thereover below its dew-point to condense out water, and the condenser serving to warm the air stream to produce effective drying conditions in the recirculated air. The air is continually drawn in from the drying cabinet and passed over the evaporator and condenser by a circulating fan and then passed back into the cabinet.
In a drying apparatus of this type water is picked up from articles in the cabinet by the warm dry circulating air and the water subsequently condensed and removed from the water vapor laden air stream by the evaporator. The water thus condensed is collected for disposal.
A particular advantage of drying apparatus of this type is the ability to completely dry totally saturated articles in a reasonably short period of time without using mechanical movement which has a damaging effect on certain materials.
2. A drying apparatus is described in British Patent specification No. 1133098 which has the characteristics above mentioned in addition to the feature of dividing the return air-flow so that only a part thereof passes through the evaporator, the remainder being bypassed. The purpose of this is an attempt to obtain optimum dehumidification conditions by passing only a small volume of the total circulating air-flow over the air cooling means. It has been found, however, that in practice whilst this arrangement does, to certain extent, increase efficiency a drying apparatus constructed in accordance with this specification cannot be made to work continuously. In other words the water extraction rate achieved at the commencement of the drying cycle will gradually decline during operation until a set of conditions within the system is reached which results in the water extraction falling to zero. The fact that such an apparatus will not function to extract water on a continuous basis, for as long as the machine is operated, is a serious disadvantage, particularly in the case of apparatus for domestic use.
It is a primary object of this invention to provide an improvement in the above apparatus to enable a continuous drying cycle to be obtained so that, irrespective of the length of time of running of the apparatus, said apparatus is always capable of extractingwater.
Another object is to provide a drying apparatus which is capable of water extraction over a widely varying range of external temperatures.
SUMMARY OF THE INVENTION within the apparatus and a bypass means whereby a part only of the air is passed over the evaporator. Alternatively, the cabinet of the drying apparatus can be constructed so as to yield part of the heat produced ex ternally to the apparatus itself.
According to another feature of the invention an auxiliary fan is used to draw off a part only of the circulating air and pass same through the evaporator for cooling. By this means a steady and controlled amount of air only is cooled at all times irrespective of the loading of the drying chamber, which greatly changes the airflow cycled through the apparatus.
The drying apparatus may be constructed as a module containing the conditioning unit and having an air inlet and outlet arranged for use with a separate cabinet which may form part of a dwelling, that is a cupboard or closet.
A drying apparatus having both the features of dividing the condenser to lose heat externally, and provision of an auxiliary fan to provide an exact and metered airflow over the evaporator, has proved in practice to be particularly advantageous and by correct design a closed dehumidification cycle can be obtained which is efficient and which will function over any length of time desired to continually extract water from wet articles.
A further advantage is that, as it has now been found that provision must be made for heat loss from the sys tern, the cabinet containing the apparatus need not be insulated, the whole acting as a balancing heatexchanger.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood from the following description taken in conjunction with the accompanying diagrammatic drawings, in which:
FIG. 1 shows a drying apparatus in which the condenser is arranged to give up part of its heat external to the apparatus.
FIG. 2 shows an apparatus of modified form in which the condenser gives up heat to water moving through the apparatus.
FIG. 3 shows an apparatus incorporating an auxiliary fan for passing a metered quantity of air over the evaporator.
FIG. 4 shows a side view of an air conditioning module incorporating a condenser arranged to give up part of its heat externally, and an auxiliary fan for passing a metered quantity of air over the evaporator.
FIG. 5 is a view looking in the direction X of FIG. 4.
FIG. 6 is a side view of a modified apparatus similar in operation to FIG. 4.
FIG. 7 is a plan view of the apparatus of FIG. 6 looking in the direction Y, and
FIG. 8 is a comparative graph.
DESCRIPTION OF THE PREFERRED EMBODIMENTS.
FIG. 1 shows a drying apparatus generally of the type described in British Patent No. 1133098 and including a drying chamber 1, including racks or rails 2 to hold articles, such as clothing, to be dried. The air conditioning unit forming part of the apparatus has an air inlet 3 and an air outlet 4, and a fan 5 arranged to circulate air from the inlet through the conditioning unit to the outlet.
The air stream at the inlet 2 is divided into two parts; roughly one third passes upwards in the direction A and then down through an air cooling means 6 comprising a finned tube forming the evaporator of a vapor compression refrigeration plant. The remaining two thirds by-passes the evaporator and passes in the direction B to recombine with the cooled air at C. The air passing through the evaporator is cooled below its dew-point and the water condensed therefrom is collected by a drip tray 7 and removed from the apparatus.
The recombined air stream C passes over the compressor 8 and receiver 9 of the refrigeration plant and is directed upwardly by the fan and over the coils 10 of the condenser forming part of the refrigerating plant and constituting an air heating means. The warm dry air emerges at the outlet 4 and may be distributed by baffles 11 into the drying chamber 2. It has been found, however, that under practical conditions articles within the chamber 2 serve to adequately distribute the airflow without additional means being provided.
According to the one aspect of this invention, in order to achieve optimum dehumidification conditions for continuous operation, means are provided to eject heat external to the apparatus, said means comprising splitting the condenser to form a second part 12 integral with the side wall 13 of the apparatus. This second part of the condenser gives up heat to warm the cabinet and hence the air surrounding same.
The apparatus of FIG. 2 embodies a drying chamber 21 defined by a perforated wall member 21a, of which the perforations at the side 21b are of smaller size than those at the side 21c to ensure substantially even air flow into the chamber 21. The air conditioning unit has an inlet 23 which again divides the air into two streams A and B. The stream A passes over the evaporator 26 of a refrigerating plant and condensed water is collected by drip tray 27.
The air stream recombines at C and is moved, by the circulating fan 25, over the compressor 28 of the refrig erating plant and then passed over condenser 30 of the refrigeration plant to an inlet zone 24 of the drying chamber.
The condenser of the refrigeration plant is divided into two parts, the one part 30 mentioned serving as the air heating means, the coils of the other part 32 being housed within the lower part of the apparatus containing water 31. An inlet 33 and outlet 34 for the water is provided which serves primarily as a medium for removing excess heat from the refrigerating cycle. A secondary feature is the use of the water for externalpurposes such as in topping up heat requirements in feed water used for washing machine installations.
The drying chamber 21 includes a rotatable drum 22 for housing articles to be dried.
In the embodiments described the dividing of the condenser has been found to produce an efficient working cycle which may be operated continuously. Under optimum conditions within the evaporator it has been found that in the heat pump cycle more heat is produced by the condenser than is absorbed by the evaporator, and if all such heat is returned to the circulating air stream then, during operation, the efficiency of the dehumidification cycle falls. By the division of the condenser to eject a part of the heat external to the apparatus, either to ambient or some suitable medium, the operating cycle can be stabilized at an optimum point. The external condenser should be sized in order to stabilize the system on the required condensing and evaporating conditions.
Ambient temperatures will also have an effect on the heat rejected externally and will affect the drying performance of the apparatus. A high ambient temperature will increase the system temperatures and pressures, and although drying performance may remain satisfactory, mechanical limitations may be exceeded. A low ambient temperature will decrease system temperatures which will decrease system temperatures, which will reduce the drying performance. The external condenser must therefore be designed taking into account the ambient temperature conditions in which the apparatus will be used.
Because heat loss is designed into the apparatus according to the invention it is unnecessary to thermally insulate the cabinet of the apparatus, and in such a case the whole cabinet may form a means for ejecting heat to the environment to produce the stabilized conditions.
When the apparatus is started there is a certain delay before water extraction commences, due to the time required before operating conditions are established. To overcome this a heater may be included to boost the drying performance during the initial warming up period. The heater may also serve to improve the operation when the apparatus us used in ambient conditions which are lower in temperature than that for which the apparatus is designed.
The drying apparatus shown in FIG. 3 incorporates an auxiliary fan in accordance with the second aspect of this invention.
As shown, a drying chamber 40 adapted to contain articles to be dried is contained within a cabinet also housing an air conditioning unit. The said unit has 'an air inlet shown generally as 41 and an air outlet 42, and includes a fan 43 for circulating air from the inlet to the outlet. Air at the inlet 41 is divided to produce a stream A which passes upwards and is drawn through an auxiliary fan 44 and then directed downwards to flow through an air cooling means 45, formed by the evaporator of a refrigeration plant 52. Water condensed out of the air by the evaporator is collected at 46. The air stream A then combines with a stream B, which bypasses the evaporator, in the zone C. The fan 43 directs the air stream over an optional electric heater 47 and upwards over the coils 48 of the condenser of the refrigeration plant, and into the drying chamber via the outlet 42. The conditioned air passes into the chamber 40 via a perforated ceiling 49 to be drawn downwards to the inlet 41, through the articles to be dried.
A desiccant bed 50 may be provided.
Air already existant in the chamber 40 is drawn through inlet stream B through the desiccant bed 50, continuing in an upward direction over the condenser coil 48 into chamber 40. Because of the designed suction pressure in the chamber percent of the air is continually recirculated direct from chamber 40 through the condenser 48. However, due to density differential, 10 percent of the moist air travels in direction A via the fan orifice and in a downward direction across the evaporator 45 and into the zone C. Air passing through the clothes in chamber 40 picks up moisture, some of which is immediately absorbed by the desiccant bed 50. The air is then further warmed by the condenser 48, completing the cycle.
The small percentage of air passing over the evaporator 45 gives up its moisture due to condensation on the evaporator coil. This process continues until such time when a sensing device in the chamber, set at a predetermined humidity, activates the fan 44 which immediately changes the percentage ratio from 90 percent to approximately 70 30 percent. The cycling of this fan in sequence with the humidity-stat creates the best situation for dehumidification which is a variable characteristic, therefore creating a maximum effect drying cycle.
When the clothes are dry an air exhaust 51 is opened and the door on the apparatus is also left open. A programmed regenerating cycle then occurs which is timed to drive off the moisture held in the desiccant bed.
In contrast to passively splitting the air-flow, the auxiliary fan allows a precise and metered quantity of air to be passed to the evaporator, regardless of the load conditions on the main fan 43 created by resistance to air-flow through the chamber 40.
Once condenser and evaporator conditions have been fixed there exists a unique air-flow that will utilize the total evaporator capacity, thereby giving the optimum dehumidification. A variation from this air flow will decrease the moisture extraction since a reduction will not use the total evaporator capacity, whereas an increased air-flow will produce an increase in the ratio of sensible to latent heat required to bring the air to or below the dew point.
It has been found that varying loadings in the chamber 40 affect the air flow rate, but by provision of the auxiliary fan the metered air flow over the evaporator results in optimum dehumidification for all loadings.
The drying apparatus shown in FIGS. 4 and 5 cmbodies both the features of the divided condenser and the auxiliary fan to produce an apparatus of particular utility for domestic purposes. The apparatus broadly comprises an air conditioning modular part 60 used in conjunction with a drying chamber 61 for housing articles to be dried. The chamber 61 can be formed by a cupboard or closet of an existing dwelling or may form, together with the unit 60, an integral apparatus.
The conditioning unit embodies a centrifugal drum fan 62 which draws air in from the chamber 61 through an inlet 63, and passes the air out back into the chamber through an outlet 64. The lower part of the unit houses the compressor 65 of a vapor compression refrigeration system, the condenser of which system is divided into two parts, the one 66 being positioned near the outlet 64 and serving as the air heating means, the other part 67 being located in a recess 68 on the side of the unit. The recess forms a cavity through which air may flow by convection over the part of the condenser 67, the assembly forming a means by which surplus heat may be ejected externally to the apparatus.
The air cooling means comprises an evaporator 69 and an auxiliary fan 70 contained within a housing in the unit. The fan 70 serves to draw off at B a metered amount of air from the circulating stream A and pass same over the evaporator where water vapor is condensed and extracted atan outlet 71. The air passes back into the main stream A at C, and the combined streams are passed over the condenser 66, serving as the heating means, and back into the chamber 61.
This apparatus embodying both features of the invention proves particularly advantageous when used in a domestic drying system, and FIG. 8 illustrates at (a) typical water extraction against time for the apparatus of FIGS. 4 and 5, whereas at (b) the extraction is shown for a system without the divided condenser and auxiliary fan. As shown by curve (b), due to conditions within the refrigeration cycle being unstabilized, the compressor will cut out after a period of operation, due to stalling, and will remain cut-off until conditions return to normal. The actual cut-off point will depend on the protector used in the compressor, but will result in a discontinuous operation as illustrated. The curve of (c) shows the typical performance of an apparatus without provision of a metered quantity of air across the evaporator, i.e. no auxiliary fan. In this case the operation is continuous but water extraction rates are much lower, representing less efficient operation.
FIGS. 6 and 7 show an apparatus similar to that of FIGS. 4 and 5 and the same references are used to indicate parts of like function. The air inlet to the conditioning unit comprises two streams A and A. The stream A passes direct to the inlet of the main fan 62, whilst the stream A is drawn in over the evaporator 69 by a smaller auxiliary fan and passed to the inlet of the main fan constituting the mixing zone C for the two air streams. The air continues through a space containing the compressor 65 and is warmed by passage over the condenser 66 and passed to the outlet 64.
The auxiliary fan 70 again provides for the passage of a precise and metered quantity of air over the evaporator 69 and performs an additional function of cooling the bearings of the main fan 62. The condenser is divided into two parts, the one 66 serving as the air heating means and the other 67 forming a convector heater located on the outer wall of the apparatus for dissipating heat externally of the apparatus.
In the embodiments of FIGS. 4 to 7 the loss of heat from the condenser part 67 may be by natural convection or assisted by forced draught.
The rate of dehumidification that can be obtained from such a system is dependent. on a number of parameters, including type and characteristics of the compressor, type of refrigerant, condensing and evaporating temperatures, air flow rate and temperature and humidity, and as heat is lost externally to the cycle, the ambient temperature. The flow rate, temperature and humidity of the air affect the mass transfer rate of moisture from the surface of items being dried and are directly connected with the drying rate that can be achieved.
At given evaporator temperature lowering the condenser temperature will increase the evaporator capacity implying a greater moisture extraction rate. This, however, produces a lowering of air temperature which is detrimental to mass transfer rates. There thus exists an ideal condenser condition for a given evaporator condition at which moisture extracted by the evaporator equals the mass transfer rate of moisture from the wet items in the airstream.
From compressor characteristics, refrigerant flow and hence evaporator duty both increase with evaporator temperature implying a greater moisture extraction rate. However, a higherair flow over the evaporator is required to utilize its total capacity. As air of percent relative humidity cannot be achieved this results in an increasing ratio of sensible to latent heat for moisture extraction. Thus for a given condenser condition there exists an optimum evaporator condition.
The invention enables these requirements to be realized in practice and provides a drying apparatus with a stabilized cycle and efficient operation.
1. An improvement in a drying apparatus including a chamber to contain articles to be dried and an air conditioning unit having air displacing means for drawing air. in from said chamber and passing same over the evaporator of a refrigerating plant, and then over the condenser of said refrigerating plant, and back into said chamber, wherein the improvement comprises in combination provision of means whereby part of the heat produced by said condenser is ejected externally of said apparatus and a bypass means whereby a part only of the air is passed over the evaporator.
2. A drying apparatus as claimed in 1, wherein the condenser is in two parts one part giving up heat to a flowable medium for use external to the apparatus.
3. A drying apparatus as claimed in claim 2, wherein the by-pass means is provided at the inlet to the air conditioning unit whereby only a part of the circulating air ing air in from said chamber and passing a part only of same over an evaporator of a refrigerating plant, the air stream then passing over the condenser of the refrigerating plant and back into said chamber, wherein the improvement comprises provision of a second auxiliary air displacing means serving to pass a metered quantity of air, constituting a part only of the air drawn in, over said evaporator, the condenser being divided into two or more parts, one of said parts serving to heat the air, the other part giving up heat externally to said apparatus.
5. A drying apparatus as claimed in claim 4, wherein the other part of the condenser is locatedin a side wall of the apparatus and forms a convector heater assisted, if necessary, by forced draft producing means.
6. A drying apparatus as claimed in claim 5, wherein the evaporator and auxiliary air displacing means comprise an assembly positioned within the air conditioning unit and located in the recirculating air stream.
7. A drying apparatus as claimed in claim 5, wherein the inlet to the air conditioning unit is divided into two parts, one part directing air over the evaporator, and incorporating the auxiliary air displacing means.
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