Problem A refrigerant space is maintained at 261 K, and cooling water is available at 294 K. Refrigeration capacity is 35.2 kW. The evaporator and condenser are of sufficient size that a 5.6 K minimum temperature difference for heat transfer can be realized in each. The refrigerant is tetrafluoroethane (HFC-134a), for which data is given in Table 9.1 and Fig G.2 (App ca). a. What is the value of COP for a Carnot refrigerator? b. Calculate COP and mass flow rate of refrigerant of the vapor-compression cycle if the compressor efficiency is 80% Solution 26)K Low-pressure vapor 255.4 K 35.2 kW Evaporator (or boiler) Low-pressure vapor-liquid mixture w Compressor Expansion turbine COP= ? W 299.6 K Condenser High-pressure vapor High-pressure liquid ec 294 K cooling water Q W W = Table 9.1 Thermodynamic Properties of Saturated Tetrafluoroethane Temperature Saturation Liquid Specific Enthalpy Entropy C pressure density volume MPa kg m kJ kg- kJ kg-'K' of vapor m kg- -40 -30 - 26.07 -22 -20 -18 -16 -14 -12 -10 -8 -6 -2 0 2 4 6 8 10 12 14 16 18 20 24 28 32 36 40 44 48 32 56 60 64 68 72 76 P 233.15 0.051 22 243.15 0.084 36 247.08 0.101 33 249.15 0.111 27 251.15 0.121 60 253.15 0.132 68 255.15 0.144 54 257.15 0.157 21 259.15 0.170 74 261.15 0.185 16 263.15 0.200 52 265.15 0.216 84 267.15 0.234 18 269.15 0.252 57 271.15 0.272 06 273.15 0.292 69 275.15 0,314 50 277.15 0.337 55 279.15 0.361 86 281.15 0.387 49 283.15 0.414 49 285.15 0.442 89 287.15 0.472 76 289.15 0.504 13 291.15 0.537 06 293,15 0.571 59 297.15 0.645 66 301.15 0.726 76 305.15 0.815 30 309.15 0.911 72 313.15 1.0165 317.15 1.1300 321.15 1.2527 325.15 1.3852 329.15 1.528 0 333.15 1.6815 337.15 1.846 4 341.15 2.0234 345.15 2.2130 349.15 2.4159 o' 14148 1385.9 1374.3 1368.2 1362.2 1356.2 1350.2 1344.1 1338.0 1331.8 1325,6 1319.3 1313.0 1306.6 1300.2 1293.7 1287.1 1280.5 1273.8 1267.0 1260.2 1253.3 1246.3 1239.3 1232.1 1224.9 1210.1 11949 1179.3 11632 1146,5 1129.2 1111.3 1092.6 1073.0 10524 1030.7 10077 983.1 956.5 V H 0.360 95 148.57 0.225 96 161.10 0.190 16 166,07 0.174 10 168.70 0.160 10 171.26 0.147 44 173.82 0.135 97 176.39 0.125 56 178.97 0.116 10 181.56 0.107 49 184.16 0.099 63 186.78 0.092 46 189.40 0.085 91 192.03 0.079 91 194.68 0.074 40 197.33 0.069 35 200.00 0.064 70 202.68 0.060 42 205.37 0.056 48 208.08 0.052 84 210.80 0.049 48 213.53 0.046 36 216.27 0.043 48 219.03 0.040 81 221.80 0.038 33 224.59 0,036 03 227.40 0.031 89 233.05 0.028 29 238.77 0.025 16 244.55 0.022 41 250.41 0.019 99 256.35 0.017 86 262.38 0.015 98 268.49 0.014 30 274.71 0.012 80 0.011 46 287.49 0.010 26 294.08 0.009 17 300.84 0.008 18 307.79 0.0X7 28 314.96 H" S 374.16 0.7973 380.45 0.8498 382.90 0.8701 384.19 0.8806 385.43 0.8908 386.66 0.9009 387.89 0.9110 389.11 0.9211 390.33 0.9311 391.55 0.9410 392.75 0.9509 393.95 0.9608 393.15 0.9707 396.33 0.9805 397.51 0.9903 398.68 1.0000 399.84 1.0097 401.00 1.0194 402.14 1.0291 403.27 1.0387 404.40 1.0483 405.51 1.0579 406.61 1.0674 407.70 1.0770 408.78 1.0865 409.84 1.0960 411.93 1.1149 413.95 1.1338 415.90 1.1527 417.78 1.1715 419.58 1.1903 421.28 1.2091 422.88 1.2279 424.35 1.2468 425.68 1.2657 426.86 1.2847 427.84 1.3039 428.61 1.3234 429.10 1.3430 429.27 1.3631 SY 1.7649 1.7519 1.7476 1.7455 1.7436 1.7417 1.7399 1.7383 1.7367 1.7351 1.7337 1.7323 1.7310 1.7297 1.7285 1.7274 1.7263 1.7252 1.7242 1.7233 1.7224 1.7215 1.7207 1.7199 1.7191 1.7183 1.7169 1.7155 1.7142 1.7129 1.7115 1.7101 1.7086 1.7070 1.7051 1.7031 1.7007 1.6979 1.6945 1.6%)5