Question

Consider an ideal refrigeration cycle that has a condenser temperature at 45°C and an evaporator temperature of -15°C. Show the process in a T-S diagram. Determine the coefficient of performance of this refrigerator for refrigerant 134a as the working fluid. Repeat the calculation for ammonia.

Answer 1

Calculation for Refrigerant R134a (0) ares 1 3 45°c т Wc I comp - Is'c 1 Gadd 2 с Property of refrigerant R134a taken from property table at T=45°C 와 hf=h₂ =hu = 115 ks /vg ha = 273 кка Sg = Б. ОТЧs /k (CP) R134 vapors - О.05 (kok at Tsat = -15°C hiang — 2ЧІ кә 0-342o К%. с S2 = S = Sg =

II Sg tepln T, Trat Siasa 0.9420 - 09145+0.95 In Tz (uiter 2328.45k or 55.45°C hza hg + cp (Tz- Trat) 273 +0.85X(328.45-318) 281.88 KST kolky ha S R134 Gadd Whet Chi-hu) Chaahi) (241–115) (Copriua 281.88-241 (CODRibua = 3,08 And

=45c calculation for ammonia Ts diagram will same as the R134a refrigerant Property of Refrigerant ammonia taken from property table at Teat hf= hz ahu = 396-8 kJ/n hg= 1474.5 KI/kg Sy = 4.825 KJ - Kh legk Cave NH3-vapor 2.2 KJ /ugh -15°C hochg 1426.6 kJ/kg S2 = S = Sg=5.548 KJ / ugk at Teat . C Tz Trat Si=S2 = Sg + cpen (17 4,825 +2.2 buc 5.548 = Tz 45+273 T2=441072k or 168.72°c hza hg to (Tz- Tsat) = 1474.5+ 22X (168.72-45) h2= 1746.68 KJ is /kg

(COD) NH3 Qadd Wrnet Chicha) Cha-hi) = (cop 1426.6 - 396.8 NH3 1746.68- 1426,6 (COD) = 3-21 NH3 And
Properties of ammonia taken from below table

Temperature Pressure Volume Specific - Ps - -V;- PC) (bar) (m²/kg) -50 -45 -40 -35 -30 -28 -26 -24 -22 -20 -18 -16 -14 -12 -10 -8 0.4089 0.5454 0.7177 0.9322 1.196 1.317 1.447 1.588 1.740 1.902 2.077 2.265 2.465 2.680 2.908 3.153 2.625 2.005 1.552 1.216 0.9633 0.8809 0.8058 0.7389 0.6783 0.6237 0.5743 0.5296 0.4890 0.4521 0.4185 0.3879 Specific Enthalpy Specific Entropy saturated saturated saturated saturated liquid vapor liquid vapor -hp- -ng -Sp- Sg (kJ/kg) (kJ/kg) (kJ/kg) (kJ/kg) -44.4 1373.3 -0.194 6.159 -22.3 1381.6 -0.096 6.057 0 1390.0 0 5.962 22.3 1397.9 0.095 5.872 44.7 1405.6 0.188 5.785 53.6 1408.5 0.224 5.751 62.6 1411.4 0.261 5.718 71.7 1414.3 0.297 5.686 80.8 1417.3 0.333 5.655 89.8 1420.0 0.368 5.623 98.8 1422.7 0.404 5.593 107.9 1425.3 0.440 5.563 117.0 1427.9 0.475 5.533 126.2 1430.5 0.510 5.504 135.4 1433.0 0.544 5.475 144.5 1435.3 0.579 5.447

36 8 40 42 A4 6 48 50 13.8 14.70 1554 6.42 17.34 18.30 13.29 20.33 0.0931 0.0380 0.0333 0.0788 0.0746 0.0706 0.0670 0.0635 3523 3621 371.3 813 918 401.3 4119 4219 14713 14726 14733 14738 1474.2 14745 1474.7 1474.7 123 1329 1.30 1391 1.422 1.453 1.484 115 4.19 4. 4.377 4.866 485 4.314 4.793 4.73

Properties of refrigerant R134a taken from below table

Temp °C sg -36.9 -31.1 -26.4 -22.3 0.9645 0.9572 0.9519 0.9478 0.9446 -18.8 0.9420 Pressure kPa 60 80 100 120 140|| 1601 1801 2001 22001 240|| 260ll 280|| 300 3201 340 3601 4001 5001 -15.6 -12.7 -10.1 -7.61 -5.4 -3.2 -1.2 0.7 2.5 4.2 5.8 8.9 15.7 21.6 26.7 31.3 35.5 R134a - TetraFlouroEthane Saturation Properties - Pressure Table (60 kPa - 3 MPa) volume ( m3/kg) enthalpy (kJ/kg) entropy (kJ/kg.K) vf vg hf hfg hg sf sfg 0.0007098|| 0.3112 3.9 223.9 227.8 0.0164 0.9481 0.0007185 0.2376 11.3 220.20 231.5 0.0472 0.9100 0.000725911 0.1926 17.3 217.2 234.51 0.07201 0.87991 0.0007324 0.1621 22.50 214.5 237.0 0.0928 0.85501 0.0007383 0.1402 27.1 212.1 239.21 0.1110 0.8337 0.0007437 0.1235 31.2 209.9 241.1 0.1270 0.81501 0.0007487 0.1104|| 35.0 207.9 242.90 0.1415 0.7982 0.0007534|| 0.0999 38.5 206.0 244.5|| 0.1547 0.7831 0.0007578 0.0912 41. 204.3 245.9 0.1668 0.7693 0.0007620 0.0839 44.7 202.6 247.3 0.1780 0.7566 0.0007661 0.0777 47.51 201.01 248.6 0.18851 0.7448 0.0007699 0.0724 50.2 199.5 249.7 0.1984 0.7338|| 0.0007737 0.0677 52.8 198.1 250.91 0.2077 0.7234 0.0007773 0.0636 55.2 196.7 251.9 0.2165 0.7137 0.0007808|| 0.0600|| 57.5 195.4 252.9 0.2248 0.7044 0.0007842 0.0567 59.8 194.1 253.8|| 0.2328 0.6956 0.00079071 0.0512|| 64.0) 191.6 255.6 0.2477 0.6793 0.000806011 0.0411 73.4 186.0 259.3 0.2803 0.6438|| 0.0008200 0.03431 81.5 180.9 262.41 0.3081 0.6138 0.0008332|| 0.0294 88.8 176.2 265.1 0.3324 0.5876 0.00084591 0.0256|| 95.5 171.8 267-3 0.3541 0.5643 0.0008581 0.0227 101.6 167.7 269.3 0.3739 0.5431 0.0008701 0.0203 107.41 163.7 271.01 0.3920 0.5237 0.00089351 0.0167 117.8 156.1 273.9|| 0.4245 0.4886 0.00091671 0.0141 127.3 148.91 276.2|| 0.45331 0.4573 0.9397 0.9378 0.9361 0.9347 0.9333 0.9322 0.9311 0.9301 0.9293 0.9284 0.9270 0.9241 0.9219 0.9200 0.9184 0.9170 0.9157 0.9131 0.9106 600/ 700|| 800ll 900 1000 12001 1400 39.4 46.3 52.4
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