Document 3ezpZjpYbMBoLJEXGEzpogO0D

796 CHAPTER 36 1952 Guide of refrigerant which is present in vapor form. Consider, for example, F-12 with a quality (the percent in vapor form) of 30 percent; the enthalpy of this material would be equal to __ where ha = A, + 0.30 (A,, -hi) ; (4) . Am = specific enthalpy of the mixture. . hi '= specific enthalpy of the liquid. h, = specific enthalpy of the saturated vapor. Values of hi and hr are obtained from Table 1 for the actual pressure of the mixture. . By a reversal of this same procedure the tabular data can be used to determine the state of a mixture leaving an expansion valve. Consider a valve to which saturated liquid at pressure p. is admitted, and a mixture of saturated liquid and vapor at pressure pa is discharged. The quality of the material at discharge is then determined by making use of the fact that the expansion process is completely irreversible, is a throttling process, and hence, occurs without change in enthalpy. Thus, the enthalpy, of the mix ture, Am, is equal to the enthalpy of the saturated liquid at the entrance state, ht., and can therefore be read from the table. Thus, . hi. = Am = hrd (1 l) (Ayd Afd) or, (5) x = (Am -- Afd) + (Avd -- Afd) (6) where hi. =? enthalpy of saturated liquid at entrance to expansion valve. Am = enthalpy of mixture. hri = enthalpy of saturated vapor at discharge. Aid = enthalpy^of liquid at discharge. x = proportion of liquid in the mixture, decimal. Vapor Compression Refrigeration Cycle Simple Cycle. The refrigerant cycle is the series of state changes (which occur in the conditioning processes) needed to restore the refrigerant to a condition in which it will possess the ability to extract heat from the space to be cooled. For all compression-type systems the cycle consists oif four processes: heat gain in the evaporator; pressure rise in the compressor; heat loss in the condenser ; pressure loss in the expansion valve. The com pression process is accomplished at the expense of energy added to the compressor in the form of shaft work, and the expansion process could be carried out, if the economics of the system would permit, in an expanding engine with consequent release of energy as shaft work. In ordinary sys tems, however, the additional first cost and maintenance costs of an expand ing engine so greatly exceed the advantage resulting from the work realized, that such engines are not used, and the pressure reduction is allowed to occur irreversibly in ah expansion valve. Basically, then, a refrigeration cycle consists of two heat transfer processes and two pressure change proc esses, no work entering into the heat transfer processes and--in the simple cycle--no heat transfer occurring during the pressure-change processes. Refrigeration 797 Table 2. Pbopebties of Monochlobodifluobomethane (F-22) Sat Temp F Abs Press Lb per Sq In. Volume. -40Enthalpy and Entropy Taken from F Enthalpy Entropy 50 Dec Superheat 100 Dec Superheat Liquid Vapor Liquid Vapor Liquid Vapor Enthalpy En tropy Enthalpy En tropy 0 38.79 0.01192 1473 io.63 105.02 0.0240 0.2293 112.35 0.2446 120.00 0.2590 ' 2 40.43 0.01195 1420 11.17 10544 0.0251 0.2289 112.59 0.2442 120.26 0.2586 4 42.14 0.01198 1.270 11.70 105.45 0.0262 0.2285 112.83 0.2438 120.52 0.2581 5 43.02 0.01200 1446 11.97 105.56 0.0268 0.2283 112.95 0.2436 120.65 0.2579 6 43.91 0.01201 1.221 12.23 105.66 0.0274 0.2280 113.07 0.2434 120.78 0.2577 8 45.74 0.01205 1.175 12.76 105.87 0.0285 0.2276 113.31 0.2430 121.04 0.2572 10 47.63 0.01208 1.130 13.29 106.08 0.0296. 0.2272 113.55 0.2426 121.30 0.2568 12 49.58 * 0.01211 1.088 1342 106:29 0.0307 0.2268 113.79 0.2422 121.56 0.2564 14 5149 0.01215 1.048 14.36 10640 0.0319 0.2264 114.02 0.2418 121.82 0.2560 16 53.66 0.01218 1.009 14.90 106.71 0.0330 0.2260 114.25 0.2414 122.08 0.2556 18 55.79 0.01222 0.9721 15.44 106.92 0.0341 0.2257 114.48 0.2410 122.33 0.2552 20 57.98 0.01225 0.9369 15.98 107.13 0.0352 0.2253 114.71 0.2406 122.59 0.2548 22 00.23 0.01229 0.9032 16.52 10743 0.0364 0.2249 114.94 0.2402 122.84 0.2544 24 6245 0.01232 0.8707 17.06 10743 0.0375 0.2246 115.17 0.2398 123.10 0.2540 26 64.94 0.01236 0.8398 17.61 107.73 0.0379 0.2242 115.40 0.2395 123.35 0.2537 28 67.40 0.01239 . 0.8100 18.17 107.93 0.0398 0.2239 115.62 0.2391 123.60 0.2533 30 32 34 ' 36 ' 38 69.93 7243 75.21 77.97 80.81 0.01243 0.01247 0.01250 0.01254. 0.01258 0.7816 0.7543 0.7283 0.7032 0.6791 18.74 19.32 . 19.90 20.49 21.09 108.13 108.33 10842 108.71 108.90 0.0409 0.0421 0.0433 0.0445 0.0457 0.2235 0.2232 0.2228 0.2225 0.2222 115.84 116.07 116.29 116.52 116.74 0.2387 0.2383 0.2380 0.2376 Q.2373 123.85 124.10 124.35 124.59 124.84 0.2529 0.2525 0.2522 0.2518 0.2515 / 42 44 46 48 83.72 86.69 89.74 9248 96.10 0.01262 0.01266 0.01270 0.01274 0.01278 0.6559 0.6339 0.6126 0.5922 04726 21.70 .22.29 22.90 23.50 24.11 109.09 10947 109.45 109.63 109.80 0.0469 0.0481 0.0493 0.0505 0.0516 0.2218 0.2215 0.2211 0.2208 0.2205 116.96 117.18 117.40 117.61 117.82 0.2369 0.2366 0.2363 0.2359 0.2350 125.08 125.32 125.56 125.80 126.04 0.2511 0.2508 0.2504 0.2501 0.2497 40 62 54 66 68 ,W ! 62 64 . 66 68 99.40 1024 106.2 1094 113.5 1174 . 121.0 124.9 128.9 133.0 0.01282 0.5537 0.01286.. 0.5355 0.01290 .0.5184 0.01294- 0.5014 0.01299 0.4849 0.01303 0.01307 0.01312 0.01316 0.01320 0.4695 0.4546 0.4403 0.4264 0.4129 24.73 25.34 25.95 26.58 2742 2743 28.46 29.09 29.72 30.35 109.98 110.14 110.30 110.47 110.63 110.78 110.93 111.08 111.22 111.35 0.0528 0.0540 0.0552 0.0564 0.0576 0.2201 0.2198 0.2194 0.2191 0.2188 0.0588 0.0600 0.0612 0.0624. 0.0636 0.2185 0.2181 0.2178 0.2175 0.2172 118.02 118.22 118.42 118.62 118.82 0.2353 0.2350 0.2347 0.2343 .2340 *126.27 126.50 126.73 126.96 127.19 no.oi 119.21 119.40 119.59 119.77 0.2337 0.2334 0.2331 0.2327 0.2324 127.42 127.65 127.87 128.10 128.32 0.2494 0.2491 0.2488 0.2484 0.2481 0.2478 0.2475 0.2472 0.2469 0.2466 70 1374 72 1414 74 145.9 76 150.4 78 155.0 0.01325 0.4000 0.01330 0.3875 0.01334 0.3754 0.01339 0.3638 0.01344 ' 0.3526 30.99 31.65 32.29 32.94 33.61 111.49 .111.63 111.75 111.88 112.01 0.0648 0.0661 0.0673 0.0684 0.0696 0.2168 0.2165 0.2162 0.2158 0.2155 119.96 120.15 120.32 120.50 120.67 0.2321 0.2318 0.2315 0.2312 0.2309 128.54 128.76 128.97 129.19 129.40 0.2463 0.2460 0.2457 0.2455 0.2452 80 82 84 86 .' 88 159.7 164.5 169.4 174.5 179.6 0.01349 0.01353 0.01358 0.01363 0.01368 0.3417 0.3313 0.3212 0.3113 0.3019 34.27 34.92 35.60 36.28 36.94 112.13 112.24 112.36 112.47 112.57 0.0708 0.0720 0.0732 0.0744 0.0756 0.2151 0.2148 0.2144 0.2140 0.2137 120.85 121.02 121.18 121.34 121.50 0.2306 0.2303 0.2300 0.2297 0.2294 129.61 129.82 130.02 130.23 130.43 0.2449 0.2446 0.2443 0.2441 0.2438 90 1844 92 190.1 94 . 195.6 96 2014 98 2064 0.01374 0.01379 0.01384 0.01390 . 0.01396 0.2928 04841 04755 0.2672 0.2594 37.61 38.28 38.97 ' 39.65 40.32 112.67 112.76 11245 112.93 113.00 0.0768 0.0780 0.0792 0.0803 0.0815 0.2133 0.2130 0.2126 0.2122 0.2119 121.66 121.82 121.97 122.12 122.26 0.2291 0.2288 0.2285 0.2282 0.2279 130.63 130.83 131.03 131.23 131.42 0.2435 ~ 0.2432 0.2429 0.2427 0.2424 100 212.6 102 218.5 104 224.6 106 230.7 108 237.0 0.01402 0.01408 0.01414 0.01420 0.01426 0.2517 0.2443 04370 0.2301 04233 40.98" 113.06 41.65 113.12 4242 113.16 42.98 113.20 43.66. 11344 0.0827 0.0839 0.0851 0.0862 0.0874 0.2115 0.2111 0.2107 0.2104 0.2100 122.40 122.53 122.66 122.79 122.92 0.2276 0.2273 0.2270 0.2267 0.2264 131.61 131.80 131.99 132.17 132.35 0.242i 0.2418; 0.2416 0.2413 0.2411 110 243.4 0.01433 0.2167 44.35 113.29 0.0886 0.2096 123.04 0.2261 132.53 0.2408 112 249.9 ' 0.01440 0.2104 45.04 113.34 0.0898 0.2093 123.16 0.2258 132.71 0.2405 114 256.6 0.01447 0.2043 46.74 113.38 0.0909 0.2089 123.28 0.2255 132.88 0.2403 116 263.4 0.01454 0.1983 46.44 113.42 0.0921 0.2085 123.40 0.2253 133.05 0.2400 118 2704 0.01461 0.1926 47.14 113.46 0.0933 0.2081 123.51 0.2250 133.22 0.2398 120 277.3 0.01469 0.1871 47.85 11342 0.0945 0.2078 123.62 0.2247 133.39 0.2395 Data from Kinetic Chemicals, Inc., 1045