NON-AZEOTROPIC REFRIGERANT MIXTURE OF R-22, R-23 AND R-152a

Abstract: A non-azeotropic refrigerant mixture is provided especially for use in heat pumps which provides improved efficiency, in terms of coefficient of performance and compressor power, than available refrigerants or mixtures thereof. The refrigerant is a ternary mixture of 4 % to 10 % R-23 (trifluoromethane), 4 % to 30 % of R-152a (1,1-difluoroethane), with the balance being R-22 (chlorodifluoromethane). The mixture can be used in heat pumps designed for R-22 without modification, and is environmentally acceptable.

Description: Non-Azeotropic Refrigerant Mixture of R-22, R-23 and R-152a 1. Technical Field: This invention relates to a non-azeotropic refrigerant mixture, especially suitable as a working fluid for heat pump applications. By use of these compositions, the cooling and heating efficiencies of heat pumps have been significantly improved. The mixture is entirely compatible with R-22 refrigerant currently used in heat pumps, and so does not require changes in the design of such heat pumps. In addition, with these compositions, the mixture appears to be environmentally acceptable. 2. Background Art: a) General The thermodynamic performance of an energy conversion device may be improved by using a non-azeotropic mixture in a vapour cycle. A non-azeotropic mixture has a temperature distribution parallel to that of the surrounding fluid with which heat transfer takes place during the evaporation and condensation processes which are part of the cycle. Interest has increased in recent years in the use of non-azeotropic refrigerant mixtures (NARM) to improve the performance of energy conversion devices. b) Prior Art Various NARM have been proposed or used in the past. Usually, these have two components, but some having three (i.e. ternary mixtures) have been proposed, for example in:- U.S. Patent No. 4,344,292 (Rojey) - issued August 17, 1982. U.S. Patent No. 4,680,939 (Rojey et al.) - issued July 21, 1987. U.S. Patent No. 4,812,250 (Ambrosino et al. ) - issued March 14, 1989. However, none of these mixtures provides the thermodynamic advantages of mixtures in accordance with this invention. Also some of the suggested components are environmentally harmful. c) Brief Description of the Drawings Reference will be made to the following drawings for a better understanding of non-azeotropic mixtures and the particular mixtures of this invention, i.e.: Fig. 1 is a temperature-entropy (TS) diagram showing the behaviour of non-azeotropic and single fluid or azeotropic mixtures at constant pressure,- Fig. 2(a) shows boiling and condensation points of a non-azeotropic mixture at various mixture concen- trations (x) , for constant pressure; Fig. 2(b) is a (TS) diagram of a hea * ^ pump cycle using a non-azeotropic mixture; Fig. 3 are pressure/temperature graphs of pure refrigerant R-22 and of a mixture in accordance with the invention; Fig. 4 shows air conditioning outlet temperatures for different refrigerant mixtures; Fig. 5 shows the coefficient of performance of a heat pump used for heating with different refrigerants; Fig. 6 shows compressor power used in a heat pump with different refrigerants; Fig. 7 shows the coefficient of performance of a heat pump used for cooling with different refrigerants; Fig. 8 shows the refrigerant mass flow rate for a heat pump with different refrigerants; Fig. 9 shows how the coefficient of performance of a heat pump used for cooling varies with the temperature of the refrigerant entering the evaporator, for different refrigerants; and Fig. 10 shows how the coefficient of performance of a heat pump used for heating varies with the temperature of the refrigerant entering the evaporator, for different refrigerants. d) The Behaviour of a Non-Azeotropic Mixture An azeotropic mixture of two substances or more cannot be separated into its components by distillation. Such a mixture evaporates and condenses as a single substance with properties that are different from those of either constituent. hereas pure substances or azeotropic mixtures have a constant phase changing temperature (e.g. boiling point) at a given pressure, non-azeotropic mixtures show separate boiling and condensing distributions, as shown in Figure 1 by the two isobaric processes fg and fg'. These lines represent, respectively, the boiling of non-azeotropic mixtures and single fluid or azeotropic mixture. Therefore, at a given composition or con- centration, the non-azeotropic mixture condenses and boils over a temperature range by an isobaric heating process 1- 2-3-4-5, as clearly shown in Figure 2a. High and low pressure regions, Pg and P L , are also shown on the pressure (p)-mass concentration (x)- temperature (T) diagram. e) Desirable Properties in Non-Azeotropic Refrigerant Mixtures are as follows :- Thermodynamic Properties 1. Low condensing pressure 2. Low boiling temperature 3. Low freezing temperature 4. High latent heat of vaporization 5. Proper P-x-T relationship 6. Low vapour and liquid specific volumes 7. Low specific heat of liquid 8. Low specific heat of vapour Physical Properties 1. High thermal conductivity of vapour 2. Low viscosity 3. Low molecular weight 4. High equilibrium mixing and solubility 5. Solubility with water 6. Solubility with lubricating oil 7. Stability Chemical Properties 1. Low degrading aspects (i.e. low Greenhouse Depletion Potential) 2. Low ozone compatibility (i.e. low Ozone Depletion Potential) Safety Properties 1. Non-flammable and Non-explosive 2. Non-toxic 3. Weak odour Economic Properties 1. Low cost and ready availability 2. High overall heat transfer coefficient Specific Properties 1. Highly non-azeotropic combination 2. High coefficient of performance (COP) 3. Low volumetric cooling capacity. 3. Disclosure of the Invention: The present invention provides a unique non- azeotropic refrigerant mixture containing R-22, R-23, and R-152a refrigerants which has a remarkably good coefficient of performance without sacrificing either the thermal capacity or environmentally desirable properties. This invention also provides a refrigerant having the above listed desirable properties. The refrigerant is particularly valuable when used in heat pumps. However, heat pumps units are often capable of use, in hot weather, as air conditioning units, and the refrigerant mixture of this invention is also suitable for air conditioner use. It may also be used in refrigerators or freezers. In accordance with one aspect of the present invention, a refrigerant comprises a ternary non-azeotropic mixture of known refrigerants, consisting essentially of: R-23 (CHF 3 ; trifluoromethane) : 4-10% R-152a (CH 3 CHF 2 ; 1,1-difluoroethane) : 4-30% R-22 (CHF2CI; chlorodifluoromethane) : Balance. The precise composition of the mixture will vary with particular working conditions. The following are examples of preferred ranges and compositions: a) Cold temperature range (0°C - 13°C) Range Preferred Composition R-23 : 4 - 6% 5% R-152a : 4 - 6% 5% R-22 : Balance 90% (composition "a 1 Very cold temperature range (-30°C - 0°C) Ran e Preferred Composition 8% 5% 87% (composition "b") c) Warm temperature range (13°C - 20°C) Range Preferred Comrosition R-23 : 4 - 6% 5% " ' 5% R-152a : 8 - 30% 20% 10% R-22 : Balance 75% 85% (composition "cτ_") (composition "C2") 4. Thermodynamic Properties of Mixture The Carnhan-Starling-DeSantis (CDS) equation of state has been employed to calculate the thermodynamic properties of the proposed non-azeotropic mixtures in the different phases. Tables 1, 2 and 3 give the thermodynamic properties including temperatures during evaporation and condensation at various pressures. The Tables are for the following preferred compositions (see above) : R-22 R-23 R-152a a) 90 5 5 b) 87 8 5 c λ ) 75 5 20 The semi-logarithmic pressure-temperature diagram displayed in Figure 3 shows that the proposed composition (C*L) behaves as a homogeneous refrigerant over the investigated range having p r e s s ure /t emper at ur e characteristics similar to R-22. This is a significant characteristic, since handling and packaging expose the refrigerant to various temperatures. The similarity to R- 22 means that standard heat pumps which use R-22 can utilize this mixture without modification. 5. Environmental Properties With the concentration of 1, 1-dif luoroethane (R- 152a) in the mixture not higher than 30% by weight, the proposed non-azeotropic mixture is nonflammable. The proposed mixture is a relatively environmentally friendly refrigerant because of the following characteristics: - Mixture components R-22, R-23, and R-152a have acceptable Ozone Depletion Potential (ODP) of 0.05, 0.00, and 0.00 respectively. The three components R-22, R-23, and R-152a also have very low Greenhouse Depletion Potential (GDP) of 0.07, 0.00, and less than 0.1 respectively. It is worthwhile mentioning that the components of the mixture R-22, R-23, and R-152a are currently mass-produced, and also meet existing regulations on the use of refrig¬ erants and their short and long term effects impact on the environment. This distinguishes the mixture of R-22, R-23 and R-152a from most of the mixtures of the above-cited patents. 6. Comparison with other Refrigerants: Performance of Mixture The mixtures of the said refrigerants as described hereby has been found to result in a very desirable mixture in attaining low evaporating temperature and a reasonable head pressure and can be used with conventional heat pumps without the requirement for any major modifications or change in equipment. The performance of a 65,000 Btu/hr. water/air heat pump using the mixture is discussed in the following. This heat pump comprises a water/refrigerant evaporator into which the mixture is introduced and from which it is discharged to a hermetic compressor for compressing the vapour mixture into an air finned condenser. After condensation, the mixture is discharged to an expansion valve; it is finally expanded through the expansion valve and recycled to the evaporator. Tests have been conducted with the refrigerant mixtures using water temperatures from 4°C to 19°C at constant air temperature of 20°C at the inlet to the air condenser. The heat pump is operated first with R-22, then with the binary mixture R-22/R-23 at 95%/5%, and finally with the proposed mixture R-22/R-23/R-152a at compositions of 85%/5%/10% (C2 above) and 75%/5%/20% (C * L above). Samples of the experimental results, obtained at entering water temperature to the evaporator of 19°C and air entering temperature to the condenser of 20°C, are displayed in Figures 4 through 8. The coefficient of performance (COP) shown in Figs. 5 and 7 is defined as the ratio of the heat power delivered by the heat pump to the electric power consumed by the motor which drives the compressor. The depicted results show that the proposed refrigerant mixture provides more desirable operating characteristics than can be attained with a single refrigerant. It will be noted that COP is significantly better using the c^ mixture (#4 in graph) than using R-22 or R-22/R-23 (#1 and #2). Although the C mixture (#3 in graph) is only moderate for COP, it does show a significant advantage in terms of compressor power (Fig. 6). Figures 9 and 10 demonstrate the effect of varying the refrigerant temperature at the evaporator side on the coefficient of performance (COP) for pure R-22, composition "a", composition "b", and composition "C * L". It is quite clear that the use of this refrigerant mixture results in an efficient COP at a cost saving in compressor maintenance and replacement. Also, as indicated above, the components are readily available and environmentally acceptable. 8 - Table 1 - Composition "a" - Cold Temperature Range R-22 - 90%: R-23 - 5%: R-152a - _5 ς * ' SATURATION PROPERTIES FOR R23 /R22 /R152A / HIIIN8 COEFFICIENT(S). 0.0000.0000.000 COflPOSITION: 0.050 MASS FRACTION > 0.060 HOLE FRACTION R23 0.900 MASS FRACTION * 0.876 HOLE FRACTION R22 0.050 HASS FRACTION = 0.064 HOLE FRACTION R152A CRITICAL TEMPERATURE TC =• 375.26 [I] CRITICAL PRESSURE PC* 5699.83 [KPA] Table 1 (Continued) - 9a - Table 1 (Continued) - 10 - Table 2 - Composition "b" - Very Cold Temperature Range R-22 - 87% : R-23 - 8% : R-152a - 5% SATURATION PROPERTIES FOR R23 /R22 /R152A / HIXINS COEFFICIENT! S): 0.000 0.000 0.000 COMPOSITION: 0.080 HASS FRACTION * - 0.096 HOLE FRACTION R23 0.870 HASS FRACTION ** 0.841 HOLE FRACTION R22 0.050 HASS FRACTION = 0.063 HOLE FRACTION R152A CRITICAL TEMPERATURE TC ' 372.47 [K] CRITICAL PRESSURE PC= 5678.22 [KPA] SUB - 11 - Table 2 (Continued) SUBSTITUTE 11a Table 2 (Continued) SUBSTITUTE SHEET - 12 - Table 3 - Composition - " c" - Warm Temperature Range R-22 - 75% : R-23 - 5% : R-1 2a - 20% 1 SATURATION PROPERTIES FOR R23 /R22 /R152A / MI I INS COEFFICIENT(S): 0.000 0.000 0.000 COMPOSITION: 0.050 HASS FRACTION = 0.058 HOLE FRACTION R23 0.750 HASS FRACTION « 0.699 HOLE FRACTION R22 0.200 HASS FRACTION = 0.244 HOLE FRACTION R152A CRITICAL TEMPERATURE TC • * *• 379.36 [K] CRITICAL PRESSURE PC * * 5639.44 [KPA] PRESSURE TEMPERATURE DENSITY ENTHALPY ENTROPY LIQ VAP LIQ VAP LIQ EVAP VAP LIQ VAP (PSIA) (Fl (LB/FTM3) — (BTU/LB) — (BTU/LB F) 55.000 I2.0B3 25.324 74.745 0.927 14.960 102.247 117.207 0.052 0.265 60.000 16.785 29.879 74.240 1.007 16.359 101.366 117.725 0.055 0.264 65.000 21.197 34.153 75.741 1.088 17.680 100.523 118.203 0.058 0.263 70.000 25.359 38.183 75.304 1.168 18.933 99.712 118.645 0.060 0.262 75.000 29.301 42.000 74.846 1.249 20.126 98.930 119.056 0.063 0.262 80.000 33.049 45.628 74.445 1.330 21.267 98.174 119.440 0.065 0.261 85.000 36.624 49.087 74.040 1.410 22.360 97.440 119.800 0.067 0.260 90.000 40.044 52.396 73.648 1.491 23.411 96.726 120.137 0.069 0.260 95.000 43.324 55.569 73.268 1.573 24.424 96.030 120.454 0.071 0.259 100.000 46.476 58.618 72.899 1.654 25.402 95.351 120.753 0.073 0.259 105.000 49.513 61.554 72.540 1.735 26.348 94.688 121.036 0.075 0.258 110.000 52.443 64.386 72.191 1.817 27.265 94.038 121.303 0.077 0.258 115.000 55.276 67.123 71.850 1.899 28.156 93.400 121.556 0.078 0.257 120.000 58.018 69.772 71.516 1.981 29.022 92.775 121.796 0.080 0.257 125.000 60.676 72.340 71.190 2.064 29.864 92.160 122.024 0.082 0.254 130.000 63.256 74.831 70.871 2.146 30.686 91.555 122.241 0.083 0.256 135.000 65.763 77.251 70.558 2.229 31.487 90.960 122.447 0.085 0.256 140.000 68.202 79.605 70.250 2.312 32.270 90.373 122.643 0.086 0.255 145.000 70.578 81.897 69.948 2.396 33.036 89.794 122.830 0.088 0.259 150.000 72.893 84.131 69.651 2.480 33.789 89.223 123.008 0.089 0.254 155.000 75.152 86.309 69.359 2.564 34.519 88.659 123.178 0.090 0.254 160.000 77.358 88.436 69.071 2.648 35.238 88.102 123.340 0.092 0.254 165.000 79.514 90.913 68.788 2.733 35.944 87.551 123.494 0.093 0.253 170.000 81.621 92.944 68.508 2.818 36.636 87.005 123.641 0.094 0.253 179.000 83.684 94.931 68.232 2.903 37.316 86.466 123.782 0.095 0.253 180.000 85.704 96.476 67.959 2.989 37.985 85.931 123.916 0.097 0.252 185.000 87.683 98.381 67.690 3.075 38.642 85.402 124.044 0.098 0.252 190.000 89.623100.248 67.424 3.162 39.289 84.877 124.166 0.099 0.252 195.000 91.525102.079 67.161 3.248 39.926 84.357 124.283 0.100 0.251 200.000 93.393103.876 66.900 3.336 40.553 83.841 124.394 0.101 0.251 205.000 95.224109.439 64.642 3.423 41.171 83.328 124.900 0.102 0.231 210.000 97.027107.370 44.387 3.911 41.781 82.820 124.601 0.103 0.250 219.000 98.797109.071 44.134 3.600 42.382 82.315 124.697 0.104 0.290 220.000100.937110.743 45.884 3.688 42.975 81.813 124.788 0.105 0.290 229.000102.249112.387 45.436 3.778 43.560 81.315 124.875 0.106 0.250 230.000103.932114.004 65.389 3.867 44.138 80.819 124.958 0.107 0.249 235.000105.590115.595 65.145 3.957 44.709 80.327 125.036 0.108 0.249 240.000107.222117.141 64.902 4.048 45.274 79.837 125.110 0.109 0.249 245.000108.829118.703 64.662 4.139 45.831 79.349 125.181 0.110 0.249 250.000110.413120.222 64.423 4.230 46.383 78.864 125.247 0.111 0.248 SUBSTITUTE SHEET - 13 - Table 3 (Continued) S UB ST /TUTE SHEET - 13a- Table 3 (Continued) 180.000 85.704 96.476 0.257 0.162 0.333 0.221 185.000 87.683 98.381 0.258 0.162 0.335 0.223 190.000 89.623 100.248 0.258 0.163 0.336 0.225 195.000 91.525 102.079 0.258 0.163 0.337 0.227 200.000 93.393 103.876 0.258 0.164 0.339 0.22B 205.000 95.226 105.639 0.258 0.164 0.340 0.230 210.000 97.027 107.370 0.259 0.165 0.342 0.232 215.000 98.797 109.071 0.259 0.165 0.343 0.234 220.000 100.537 110.743 0.259 0.166 0.345 0.236 225.000 102.249 112.387 0.259 0.166 0.346 0.238 230.000 103.932 114.004 0.259 0.167 0.348 0.239 235.000 105.590 115.595 0.259 0.167 0.349 0.241 240.000 107.222 117.161 0.259 0.168 0.351 0.243 245.000 108.829 118.703 0.260 0.168 0.353 0.245 250.000 110.413 120.222 0.260 0.169 0.354 0.247 255.000 111.974 121.718 0.260 0.169 0.356 0.249 260.000 113.513 123.193 0.260 0.170 0.357 0.251 265.000 115.030 124.647 0.260 0.170 0.359 0.253 270.000 116.527 126.081 0.260 0.171 0.361 0.255 275.000 118.004 127.495 0.260 0.171 0.362 0.257 280.000 119.462 128.890 0.260 0.172 0.364 0.259 285.000 120.900 130.267 0.260 0.172 0.366 0.262 290.000 122.321 131.626 0.260 0.173 0.36B 0.264 295.000 123.725 132.968 0.260 0.173 0.369 0.266 300.000 125.111 134.293 0.261 0.174 0.371 0.268 SUBSTITUTE SHEET

Claims: - 14 - CLAIMS 1. A non-azeotropic refrigerant mixture which is a ternary mixture of known refrigerants, characterized in that it consists essentially of: trifluoromethane (R-23) 4% to 10% 1, 1-difluoroethane (R-152a) 4% to 30% chlorodifluoromethane (R-22) Balance. 2. A non-azeotropic refrigerant mixture according to claim 1, consisting essentially of: 3. A non-azeotropic refrigerant mixture according to claim 1, consisting essentially of: 4. A non-azeotropic refrigerant mixture according to claim 1, consisting essentially of: 5. A non-azeotropic refrigerant mixture according to claim 1, consisting essentially of: 6. A non-azeotropic refrigerant mixture according to claim 1, consisting essentially of: - 15 - 7. A non-azeotropic refrigerant mixture according to claim 1, consisting essentially of: 8. A non-azeotropic refrigerant mixture according to claim 1, consisting essentially of: 9. A heat transfer process of the kind using a heat pump, and wherein a refrigerant is successively evaporated while extracting heat from a heat source and then condensed while giving heat to receiving fluid, and wherein the refrigerant is a non-azeotropic ternary mixture of known refrigerants, characterized in that it consists essentially of: trifluoromethane (R-23) 4% to 10%; 1,1-difluoroethane (R-152a) 4% to 30%; chlorodifluoromethane (R-22) Balance. 10. A heat transfer process according to claim 9, wherein the heat source has a temperature range between 0°C and 13°C, and wherein the refrigerant is a non-azeotropic ternary mixture consisting essentially of: 11. A heat transfer process according to claim 9, wherein the heat source has a temperature range between -30°C and 0°C, and wherein the refrigerant is a non-azeotropic ternary mixture consisting essentially of: R-23 : 7% to 10%; R-152a : 4% to 6%; - 16 - R-22 : Balance . 12. A heat transfer process according to claim 9, wherein the heat source has a temperature range between 13°C and 20°C, and wherein the refrigerant is a non-azeotropic ternary mixture consisting essentially of: 13. A heat pump having a refrigerant as claimed in claim 1. 14. A heat pump having a refrigerant as claimed in claim 2. 15. A heat pump having a refrigerant as claimed in claim 4. 16. A heat pump having a refrigerant as claimed in claim 6.

Inventors: SAMI SAMUEL, SAMI, SAMUEL
Applicants: UNIV MONCTON, UNIVERSITY OF MONCTON
Application year: 1992
Main classification: C09K5
IPC codes: C09K5