US 3277659 A
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Oc 1966 s. G. SYLVAN ETAL REFRIGERATION Filed July 17, 1964 EXP. 20 h VALVE 22 HEAT Z I EXCHANGER J -'-|s 2e CONDENSER l4 s v mon e T 24 EVAPORATOR 2 6 A 4 MIXER no I CYCLE WITH VAPOR SEPARATION 7 3/6 I I 'LIQUID REFRIGERANT LINE I6\ 2a 2o EXF. VALVE22 ff HEAT a EVAPORATOR g; 176 2 CONDENSER. I4 24 PUMP2 CYCLE WITH LIQUID SEPA RATION SATURATION CURVE CONDENSER PRESSURE CONDENSER TEMPERATURE ENTROPY LIQUID REFRIGERANT LINE I63 uoum SEPARATOR 32E LIQUID CARRIER uoum um: a
E 'HEF RIGERANT LEVEL INVENTORS NOLD B. MEDBERY STIG G. SYLVA N ORNEE ATT United States Patent M 3,277,659 REFRIGERATION Stig G. Sylvan, Louisville, Ky., and Arnold B. Medbery, Moline, Ill., assignors to American Air Filter Company, Inc., Louisville, Ky., a corporation of Delaware Filed July 17, 1964, Ser. No. 383,417 Claims. (Cl. 62-114) saturated refrigerant vapor passing from the evaporator is superheated at a substantially constant pressure to a temperature substantially equal to the condensing temperature of the refrigerant and this superheated vapor is then substantially isothermally compressed, instead of being isentropically compressed as in the conventional cycle. In other respects, the cycle of this invention may be considered to generally correspond with the conventional refrigeration cycle.
In carrying out the invention, it is essential that the refrigerant vapor be superheated before compression to a temperature approximating the condensing temperature and that the compression of the vapor be substantially isothermal. To accomplish this isothermal compression of the refrigerant vapor, it is presently contemplated that a carrier liquid and a foaming agent be mixed with the vapor so that a foamed mixture of the liquid and vapor is formed for passage through the compression device. The presence of the carrier liquid permits the isothermal compression of the vapor to take place. Thus one salient feature of the invention resides in the addition of heat to the refrigerant in the superheating stage rather than in the compression stage so that all that need take place with respect to the refrigerant during the compression stage is an increase in pressure without the corresponding conventional increase in temperature of the refrigerant.
In the drawing:
FIGURE 1 is a diagrammatic view of one form of apparatus incorporating the principles of the invention;
FIGURE 2 is a diagrammatc view of another form of apparatus incorporating the principles of the invention; and
FIGURE 3 is a temperature-entropy diagram illustrating the relationship between an idealized conventional refrigeration cycle and an idealized refrigeration cycle of this invention.
Referring now to the diagrammatically illustrated apparatus in FIGURE 1, the compression pump 2 has its outlet connected by a mixture line 4 to the inlet of a vapor-liquid separator 6. The carrier liquid outlet adjacent the bottom of the separator 6 is connected by a carrier liquid line 8 to a foam mixer 10 adjacent the pump inlet. The mixer 10 preferably includes a nozzle through which the liquid is discharged as a jet which entrains the refrigerant vapor to form a foam. This also tends to regain the energy in the carrier liquid exiting from the liquid line at a substantially higher pressure than the pressure on the suction side of the pump 2. The refrigerant vapor outlet adjacent the top of the separator 6 is connected by vapor line 12 to the refrigerant condenser 14.
3,277,659 Patented Oct. 11, 1966 The condenser 14 outlet is connected by one liquid refrigerant line 16 through a high efiiciency heat exchanger 18 and then another liquid refrigerant line 20 to an expansion device 22. Expansion device 22 is in turn connected by line 24 to the inlet of the refrigerant evaporator 26 whose outlet is connected by vapor line 28 to the heat exchanger 18 and thence through line 30 to the foam mixer 10.
In the FIG. 1 embodiment of the invention, the path of the refrigerant is generally conventional in that it passes from pump 2 to condenser 14, expansion device 22, and evaporator 26 back to the pump, the direction of flow of this refrigerant through the circuit being indicated by the solid line arrows. The path of the carrier liquid, which accompanies the refrigerant in this embodiment between the foam mixer 10 and separator 6, has its flow direction indicated by the broken line arrows.
In operation of the apparatus of FIGURE 1, the suction pressure of pump 2 induces the flow into the pump inlet of the carrier liquid and foaming agent from line 8, and the superheated refrigerant vapor returning through line 30 from the heat exchanger 18. The difference in pressure between the liquid line 8, and the suction side of the pump 2, results in the liquid issuing from line 8 as as high velocity jet out of the nozzle shown in broken lines in the mixer 10. Thus the three components, the
superheated refrigerant vapor, the foaming agent, and the carrier liquid form a foamy mixture which is compressed and pumped through mixture line 4 into the vapor-liquid separator 6. In the separator, the foam is broken down by settling in vapor separator 6 or appropriate mechanical or other means, freeing the refrigerant vapor for passage through line 12 to the condenser while the carrier liquid component of the mixture remains in the separator 6 for recirculation back to the mixer and pump through liquid line 8. Condensation of the refrigerant vapor takes place in the condenser 14' and it then flows through liquid refrigerant line 16 to the heat exchanger for subcooling, and through the remainder of the refrigerant circuit as previously described.
The embodiment shown in FIG. 2 corresponds in all respects with that shown in FIG. 1 except for the separator designated 32 following the condenser 14 instead of preceding it. The carrier liquid accompanies the refrigerant through the condenser, where the refrigerant vapor is condensed, with no attempt being made to separate the components until they both reach the separator 32 in liquid form. I Thus the primary difference in operation is that a liquid-liquid separation takes place rather than a vapor-liquid separation. The refrigerant in liquid form is assumed to have a greater specific gravity than the carrier liquid for purposes of illustration, but it will be appreciated that if the reverse were true the respective connecting locations of the carrier liquid line and refrigerant liquid line would be reversed on the separator 32.
The departures of the subject refrigeration cycle relative to a conventional refrigeration cycle are perhaps best perceived in connection with the idealized diagram of FIGURE 3 illustrating the relationship between absolute temperature and entropy of the refrigerant in the cycle. The successive conditions of the refrigerant for the subject cycle, starting with saturated refrigerant vapor leaving the evaporator, are represented by the letters ABDE'FGA. The successive conditions of refrigerant in a conventional cycle are indicated by the points ABCDEFGA assuming that the vapor was superheated to the extent shown in the diagram between points A and B. This degree of superheat is exaggerated herein since typically the degree of superheat in a conventional cycle would be only enough to insure the absence of refrigerant in a liquid state passing into the compressor.
Considering now the subject refrigeration cycle, point A in the diagram represents the saturated vapor condition of the refrigerant leaving the evaporator 26 and passing into the heat exchanger 18 where it is superheated along the constant pressure line A-B until its temperature approximates the condenser temperature on the level of point B. This high degree of superheat is imparted to the refrigerant vapor in the heat exchanger 18 before it flows into the foam mixer 10 for mixing With the carrier liquid out of line 8 and the foaming agent. The foamed carrier liquid-superheated refrigerant vapor mixture is drawn into the pump 2 and the pressure of the mixture is increased by the pump from the pressure level in the evaporator and heatexchanger to the condenser pressure. By virtue of the presence of the carrier liquid in the mixture, the compression of the refrigerant along the line B to D is substantially isothermal. After the compression step, the mixture is passed into the vaporliquid separator 6 if the apparatus of FIG. 1 is being 'used, or directly into the condenser if FIG. 2 apparatus is used. In either case the temperature-entropy diagram is the same, since it is the condition of the refrigerant alone which is there represented. If the FIG. 1 system is used, the carrier liquid and foaming agent are separated from the saturated vapor refrigerant in the separator 6 so that'only the refrigerant passes into the condenser 14, while in the FIG. 2 arrangement the carrier liquid accompanies the refrigerant through the condenser while the refrigerant is condensing as indicated by the line D-E on the diagram.
When the refrigerant reaches point B on the diagram, all of the refrigerant vapor has condensed into refrigerant liquid and this refrigerant liquid passes through line 16 into the heat exchanger 18 for subcooling at a constant pressure along the line E-F of the diagram. The heat released during this subcooling step is used for the superheating process A-B. Due to the difierences in the specific heat of the refrigerant as a liquid as compared to the refrigerant as a vapor, less heat is required for superheating the vapor from the evaporator temperature to the condenser temperature than is required to subcool the liquid from the condenser temperatures to the evaporator temperature. Consequently the temperature to which the liquid refrigerant is depressed during subcooling will be above the evaporator temperature, as is indicated by the point F which is slightly off the liquid refrigerant part of the saturation curve.
The subcooled refrigerant liquid is passed through the expansion device 22 Where it expands along the constant enthalpy line F-G. The primarily liquid (partly vapor) refrigerant at point G corresponds to the condition of the refrigerant as it enters the evaporator, and line G-A of course corresponds to the condition of the refrigerant as it passes through the evaporator and is re-evaporated. The saturated vapor indicated at point A corresponds to the condition of the refrigerant as it enters the heat exchanger 18 through line 28, the heat exohangenas noted before, serving to impart the high superheat condition to the refrigerant vapor before it again enters the mixer 10 and pump 2.
For the purposes of comparison of the subject cycle with a generally conventional cycle, it is assumed in the FIG. 3 diagram that a compression step in a generally conventional refrigeration cycle is carried out upon refrigerant vapor having the degree of superheat indicated by point B. If such superheated refrigerant vapor were introduced into the pump without an accompanying vehicle taking the heat of compression from the refrigerant, then in the pump the refrigerant vapor would be isentropically compressed along the line B-C and then would be cooled at a constant pressure along the lines -D and D-E in the condenser. It is also assumed that the remainder of the cycle is carried out by subcooling ,(E-F), expansion (F-G), and evaporation (G-A), as has been previously described.
Now comparing the conventional cycle including the isentropic compression, and our cycle with the isothermal compression, in both cases the heat removed from the medium being cooled by the evaporator is the same and is represented by the area under the line GA. In the case of our cycle the external work done is represented by the area within the closed figure ABDEFGA, while in the case of the conventional cycle the work done is represented by the area within the enclosed figure ABDEFGA, while in the case of the conventional cycle the work done is represented by the area within the enclosed figure ABCDEFGA. The generally triangular area BCD in the conventional cycle represents the additional external work required in a conventional cycle as compared to our cycle.
The difference between our cycle and a conventional cycle is thus graphically emphasized by the area enclosed Within the triangle BCD, and it is precisely for this reason that the conventional refrigeration cycle is represented in the diagram as including a superheating step (line A-B) of highly exaggerated degree. If it were assumed that in a conventional refrigeration cycle virtually no superheat was added to the vapor before being isentropically compressed along the broken line A-H of FIGURE 3, it might be said that in this case the triangular area KHD is substantially less than the triangular area ABK, these two areas representing the differences in the external work of the two cycles. However, in the case of a conventional cycle wherein no superheat is added to :the saturated vapor at point A before isentropic compression (A-H) thereof, then by the same token the subcooling indicated along the line E-F of the diagram is not available before expansion of the liquid refrigerant, and consequently the expansion line will fall generally along the broken line E-I. Hence it will be apparent that the heat removed from the medium being cooled by the evaporator is in such a case represented by the area under the line J-A rather than under the line G-A, and again the difference between the cycles is evident.
Passing now from the comparison of our cycle with a cycle including isentropic compression, as graphically portrayed in the idealized cycles, it is noted that by virtue of the presence of the carrier liquid in the compression stage it is effectively a liquid which is being pumped rather than a vapor. Since the pressure developed by a centrifugal pump is proportional to the product of density of the medium being handled and the square of the .tip speed, it will be readily appreciated that by increasing the density of the pumped medium to the degree afforded by the addition of a liquid to the vapor, much greater pressures can be developed by a given centrifugal pump or, alternatively, the pump may be much smaller and still develop a given pressure. Thus, by utilizing our invention, the application of refrigeration systems using centrifugal compressors is substantially extended.
In the embodiment illustrated in FIGURE 1, wherein the refrigerant is separated from the carrier liquid and the foaming agent before the condenser, it will be appreciated that to prevent condensation of the vaporous refrigerant in the vapor-liquid separator 6 the temperature of the carrier liquid in its contact with the refrigerant vapor should correspond generally with the temperature of the condenser 14. Thus, at least for initial startup of the apparatus, heating means for example, a heating coil 6' which may be be steam or electric, may be provided in the separator 6 to increase the temperature of the carrier liquid to the level of the refrigerant condensing temperature so that the refrigerant vapor does not condense in the pump or separator instead of the condenser 14. Depending upon the character of the pump 2, after startup sufiicient heat may be generated by the pump to maintain the carrier liquid temperature at a value preventing any substantial loss of superheat before compression, and preventing condensation in the separator or, alternatively, heating from the external source may be continued in the separator 6 to a greater or lesser degree in accordance with indicated need.
With the FIG. 2 apparatus, wherein the refrigerant is condensed before separation from the carrier liquid, such external heating means need not be employed since condensation of refrigerant in the carrier liquid is not detrimental. While an initial period of relatively ineffective operation may take place while the temperature of the carrier liquid is rising toward the condensing temperature, when the carrier liquid temperature reaches the elevated temperature the cycle will be carried out as described.
The description of the invention concept has proceeded in connection with the apparatus examples of FIG. 1 and 2, but it is to be understood that other arrangements may be used to carry out the invention. As an example, the pump may be used to pump the liquid only in a circuit which includes a jet compressor to which the superheated refrigerant vapor is introduced. In this case the energy of the high velocity liquid jet discharged into the jet compressor is utilized to effect the isothermal compression of the refrigerant vapor, and it is again the presence of the carrier liquid which permits the isothermal compression.
In another case the heat exchanger 18 of FIG. 2 is deleted. The refrigerant vapor leaving the evaporator at the evaporator temperature is mixed directly into the carrier liquid having substantially the condenser temperature. The resulting mixture temperature will be somewhat less than the condenser temperature depending on the particular heat capacity ratio between refrigerant vapor and can'ier liquid. Point U in the chart of FIG. 3 may represent the temperature and pressure of the vapor after mixing.
The isothermal compression in the pump starts from point U. As the pressure is gradually increased a saturated condition is reached at point V. At this point the refrigerant starts to condense. Further compression causes an increase in the temperature of the mixture as indicated by line VW in the chart. The latent heat of the condensed vapor corresponds to the increase in sensible heat of the mixture. At point W the condenser temperature has been reached and further latent heat is absorbed in the condenser.
The deletion of the heat exchanger is applicable only in an arrangement as in FIG. 2. Of course, the subcooling indicated along line E-F is not available.
The invention claimed is: 1. In a refrigeration method: superheating a vaporous refrigerant to a temperature approximating the condenser temperature; and
then passing said vaporous refrigerant through a compression device along with a liquid medium, also having a temperature approximating said condenser temperature, to effect a substantially isothermal compression of said vaporous refrigerant.
2. In a refrigeration method:
pump a superheated refrigerant vapor having a temperature approximating the condenser temperature of said refrigerant, along with a liquid of approximately said temperature, to effect a substantially isothermal pressure increase of said refrigerant vapor to the condenser pressure; and
effecting substantially all of said superheating of said refrigerant vapor before the pumping step by passing it in heat exchanging relation with condensed refrigerant undergoing subcooling before expansion thereof.
3. In a refrigeration method:
pumping a foamed mixture of a carrier liquid and a superheated refrigerant vapor, both having a temperature approximating the condenser temperature of said refrigerant, to increase the pressure of said refrigerant vapor substantially isothermally to the condenser pressure;
then condensing, subcooling, expanding, and evaporating said refrigerant; and
then superheating said refrigerant vapor, before pumping, to said temperature approximating said condenser temperature.
4. In a refrigeration method:
circulating a refrigerant through a refrigeration system;
circulating a liquid medium having a temperature approximating the condenser temperature of said refrigerant through the compression stage of said system along with said refrigerant;
superheating said refrigerant, returning from the evaporator of said system, to a temperature approximating said condenser temperature and before mixing said refrigerant with said liquid medium'for passage through said compression stage; and
separating said refrigerant from said liquid medium after said compression stage and before said refrigerant is passed into heat exchanging relation to superheat said returning refrigerant.
5. In a refrigeration method:
superheating a saturated refrigerant vapor to a temperature approximating the condenser temperature of said refrigerant;
compressing said superheated refrigerant vapor, along with a carrier liquid having approximately said condenser temperature, to increase the pressure of said liquid and said vapor to the condenser pressure at said condenser temperature so that the compression of said refrigerant vapor is substantially isothermal.
6. In a refrigeration method:
pumping a foamed carrier liquid-superheated refrigerant vapor mixture having a temperature approximating the condenser temperature to increase the pressure of said vapor substantially isothermally to a value at which said vapor is saturated;
circulating the refrigerant successively through a condensing stage, an expansion stage, and an evaporating stage; and
passing the refrigerant vapor leaving said evaporating stage in heat exchanging relation with the liquid refrigerant leaving said condensing stage to superheat said refrigerant vapor to a temperature substantially equalling said condenser temperature, and to subcool said liquid refrigerant.
7. In a refrigeration method:
mixing a liquid having a temperature approximating the refrigerant condensing temperature with a superheated refrigerant vapor of about the same temperature along with a foaming agent to effect a foamed mixture;
increasing the pressure of said mixture to a value corresponding to the pressure at which said refrigerant is to be condensed;
separating the saturated vapor refrigerant from said liquid;
circulating said refrigerant successively through a condensing stage, an expansion stage, and an evaporating stage; and
passing the refrigerant vapor leaving said evaporating stage in countercurrent heat exchanging relation with the liquid refrigerant passing from said condensing stage to said expansion stage to effect said superheating of said vapor before said mixing step.
8. In a refrigeration system including a refrigerant,
a compressor, a condenser, a refrigerant expansion device, and an evaporator:
means for superheating said refrigerant to a temperature approximating the condensing temperature of said refrigerant before admitting said refrigerant to said compressor;
means for circulating a medium in a liquid state, at a temperature approximating the refrigerant condensing means for separating said refrigerant from said liquid medium at a point in said system preceding passage of the refrigerant in condensed form into said means for superheating.
9. In a system as specified in claim 8:
said separator means comprises a vapor-liquid separator between said compressor and said condenser.
10. In a system as specified in claim 8:
said separator means comprises a liquid-liquid separator between said condenser and said means for superheating.
UNITED STATES PATENTS Davenport 62 -114 Seligmann 62--114 Randel 62-116, Japolsky 165-66 X Donovan 62-513 X Dubitzky 62114 Rigney 625 13 X Nebgen 621 14 X Wile et a1. 62513 X LLOYD L. KING, Primary Examiner.
ROBERT A. OLEARY, Examiner.