Document 7RKrnxR3VXp43eyp1zazwEj0e

680 CHAPTER 39 ' ' ______ 1946 Guide medium; under these conditions heat transfer is established from the refrigerant vapor to the cooling medium with resultant condensation of the refrigerant. When condensed, the high-pressure liquid refrigerant is reduced in pressure and again allowed tp boil in the evaporator. Thermodynamically, a material for use as a refrigerant should have a large latent heat of vaporization since it is this heat quantity---subject to minor variations--which constitutes the working effectiveness of the refrigerant. Further, since the work required to compress a vapor increases rapidly with the pressure range, the thermodynamic character istics of the fluid should be such that the required low-to-high temperature range can be achieved withonly a moderate change in pressure. A further consideration, from the standpoint of practical operating effectiveness, is that the suction pressure should not be below atmospheric (to prevent leakage of air into the refrigerant lines) nor should the condenser pressure be excessively high (to prevent need for extra-heavy construction). The specific volume-specific enthalpy relationship is also important'because some materials'would have such low density, when, in vapor form, that impractical compressor displacements would be needed to handle the suction vapor. Properties of refrigerants are usually given either in tabular or graphic form. In contrast to the temperature-entropy plotting which is used almost exclusively in steam-power work, refrigeration problems are usually referred to a pressure-enthalpy chart. The advantage of pressureenthalpy plotting is that linear distances on the chart correspond to energy gains or. losses and the two types of processes, constant-pressure and constant-enthalpy, which occur most frequently in refrigeration cycles, can both be represented by straight vertical or horizontal lines. Tabular arrangements of refrigerant properties have the disadvantage common to all point representations, in requiring interpolation between given values, but have the advantage of an accuracy greater than that obtainable from a chart. Tables 1, 2, 3, 4, 5, 6 and 7 give the thermo dynamic properties of seven of the more common refrigerants: dichlorodifluoromethane (F-12), monochlorodifluoromethane (F-22), methyl, chloride, ammonia, carbon dioxide, monofluorotrichloromethane (F-ll), and water; the first five of these materials are'commonly used in recipro cating compressors, the last two in centrifugal machines, while water also finds use in steam jet systems. Referring to Table 1, the first column gives the range of saturation temperatures likely to occur in practice. The second column gives the saturation pressure expressed in pounds per square inch absolute corre sponding to a given temperature, while the next six columns give the three fundamental specific properties, volume, enthalpy, and entropy, of the saturated liquid and saturated vapor respectively. The last four columns give specific enthalpy and specific entropy for gases with 25 deg and with 50 deg of superheat; note' particularly that the column heading SO F superheat means, not that the gas is at a temperature of 50 F, but that its temperature exceeds by 50 deg the saturation tempera ture corresponding to its actual pressure. Thus F-12 vapor at 38.0 psig and 91 F possesses 50 deg of superheat since its saturation temperature corresponding to 52.7 psia is 41 F. The tabular arrangements of refrigerant properties are literally for saturated or superheated materials only. In many cases, however, the engineer must work with sub-cooled liquids. With an accuracy sufficient for all practical purposes the specific volume and specific enthalpy of any Refrigeration 681 Table 1. Properties op Dichlorodifluoromethane(F-12) Sat. Tbkp. P ABS. Press. Lb pbb Sq In. Volukb Liquid Vapor Specific Enthalpy and Entropy Taken From -- 40 F Specific Enthalpy Entropy 25 F Superheat 50 F Superheat Liquid Vapor liquid Vapor Sp. En. Entropy Sp. En. Entropy 0 2 4 5 6 *108 12 14 16 18 20 22 24 26 28 30 32 34 36 38 39 40 41 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100 102 104 106 108 110 112 114 116 118 120 122 124 126 128 130 t32 134 136 138 140 23.87 24.89 25.96 26.51 27.05 28.18 29.35 30.56 31.80 33.08 34.40 35.75 37.15 38.58 40.07 41.S9 43.16 44.77 46.42 48.13 49.88 50.78 51.68 52.70 53.51 55.40 57.35 59.35 61.39 63.49 65.63 67M 70.10 72.41 74.77 77.20 79.67 82.24 84.82 87.50 90.20 93.00 95.85 98.76 101.70 104.8 107.9 111.1 114.3 117.7 121.0 124.5 128.0 131.6 135.3 139.0 142.8 146.8 150.7 154.8 158.9 163.1 167.4 171.8 176.2 180.8 185.4 190.1 194.9 199.8 204.8 209.9 215.0 220.2 0.0110 0.0110 0.0111 0.0111 0.0111 1.637 1.574 1.514 1.485 1.457 8.25 8.67 9.10 9.32 9.53 0.0111 0.0112 0.0112 0.0112 0.0112 1.403 U51 1.301 1.253 1.207 9.96 1049 10.82 1146 11.70 0.0113 0.0113 0.0113 0.0113 0.0114 1.163 1.121 1.081 1.043 1.007 12.12 . 12.55 13.00 13.44 13.88 0.0114 0.0115 0.0115 0.0115 0.0116 0.973 0.939 0.908 0.877 0.848 14.32 14.76 1541 15.65 16.10 0.01L6 0 0116 0.0116 0.0116 0.0116 0.819 0.806 0.792 0.779 0.767 1645 16.77 17.00 17.23 17.46 0.0117 0.0117 0.0117 0.0118 0.0118 0.742 0.718 - 0.695 0.673 0.652 17.91 1846 18.82 19.27 19.72 0.0118 0.0119 00119 0.0119 0.0120 0.632 0.612 0.593 0.575 OJ57 20.18 20.64 21.11 2147 22.03 0.0120 0.0120 0.0121 0.0121 0.0121 0.540 0.524 0.508 0.493 0.479 22.49 22.95 23.42 23.90 24.37 0.0122 0.0122 0.0123 0.0123 0.0123 0.464 0.451 0.438 0.425 0.413 24.84 2542 2540 26.28 26.76 0.0124 0.0124 0.0124 0.0125 0.0125 0.401 0.389 0.378 0.368 0.357 27.24 27.72 28.21 28.70 29.19 0.0126 0.0126 0.0126 0.0127 0.0127 0447 0.338 0.328 0.319 0410 29.68 30.18 30.67 31.16 31.65 0.0128 0.0128 0.0129 0.0129 . 0.0130 0.302 0.293 0.285 0.277 0.269 32.15 32.65 33.15 33.65 34.15 0.0130 0.0131 . 0.0131 0.0132 0.0132 0.262 0454 0447 0.240 0.233 34.65 35.15 35.65 36.16 36.66 0.0133 0.0133 0.0134 0.0134 0.0135 0.227 0.220 0.214 0.208 0.202 37.16 37.67 38.18 38.69 39.19 0.0135 0.0136 0.0137 0.0138 0.196 0.191 0.185 0.180 . 39.70 40.21 40.72 41.24 7841 78.44 78.67 78.79 78.90 79.13 7946 7949 7942 80.05 80.27 80.49 80.72 80.95 81.17 8149 81.61 8143 82.05 8247 82.49 82.60 82.71 8242 82.93 83.15 83.36 83.57 83.78 83.99 84.20 84.41 84.62 8442 85.02 85.22 85.42 85.62 85.82 8602 86.22 86.42 86.61 86.80 86.99 87.18 8747 87.56 87.74 87.92 88.10 88.28 88.45 88.62 88.79 88.95 89.11 89.27 89.43 89.58 89.73 8947 90.01 90.15 90.28 90.40 90.52 90.64 90.76 90.86 90.96 91.06 91.15 9144 0.01869 0.01961 0.02052 0.02097 0.02143 0.17091 0.17075 0.17060 0.17052 0.17045 81.71 81.94 82.17 82.29 82.41 0.02235 0.02328 0.02419 0.02510 0.02601 0.17030 82.66 0.17015 82.90 0.17001 83.14 0.16987 8338 0.16974 83.61 0.02692 0.02783 0.02873 0.02963 0.03053 0.16961 0.16949 0.16938 0.16926 0.16913 83.85 84.09 84.32 8435 84.79 0.03143 0.03233 0.03323 0.03413 003502 0.16900 0.16887 0.16876 0.16865 0.16854 85.02 85.25 85.48 85.71 85.95 0.03591 0.03635 0.036S0 0.03725 0.03770 0.16843 0.16838 0.16833 0.16828 0.16823 86.18 86.29 86.41 8632 86.64 0.03859 0.03948 0.04037 0.04126 0.04215 0.16813 0.16803 0.16794 0.16785 0.16776 86.86 87.09 8731 87.54 87.76 0.04304 0.04392 0.04480 0.04568 0.04657 0.16767 0.16758 0.16749 0.16741 0.16733 87.98 88.20 88.42 88.64 88.86 0.04745 0.04833 0.04921 0.05009 0.05097 0.16725 0.16717 0.16709 0.16701 0.16693 89.07 89.29 89.50 89.72 89.93 0.05185 0.05272 0.05359 0.05446 0.05534 0.16685 0.16677 0.16669 0.16662 0.16655 90.14 90.36 9037 90.78 90.98 0.05621 0.05708 0.05795 0.05882 0.05969 0.16648 0.16640 0.16632 0.16624 0.16616 91.18 9137 9137 91.77 91.97 0.06056 0.06143 0.06230 0.06316 0.06403 0.16608 0.16600 0.16592 0.16584 0.16576 92.16 9236 9235 92.75 92.93 0.06490 0.06577 0.06663 0.06749 0.06836 0.16568 0.16560 0.16551 0.16542 0.16533 93.11 93.30 93.48 93.66 93.82 0.06922 0.07008 0.07094 0.07180 0.07266 0.16524 0.16515 0.16505 0.16495 0.16484 93.98 94.15 94.31 94.47 94.63 0.07352 0.07437 0.07522 0.07607 0.07691 0.16473 0.16462 0.16450 0.16438 0.16425 94.78 94.94 95.09 95.25 95.41 0.07775 0.07858 0.07941 0.08024 0.16411 0.16396 0.16380 0.16363 9536 95.72 9537 96.03 0.17829 0.17812 0.17795 0.17786 0.17778 0.17763 0.17747 0.17733 0.17720 0.17706 0.17693 0.17679 0.17666 0.17652 0.17639 0.17625 0.17612 0.17600 0.17589 0.17577 0.17S66 0.17560 0.17554 0.17549 0.17544 0.17534 0.17525 0.17515 0.17505 0.17496 0.17486 0.17477 0.17467 0.17458 0.17450 0.17442 0.17433 0.17425 0.17417 0.17409 0.17402 0.17394 0.17387 0.17379 0.17372 0.17365 0.17358 0.17351. 0.17344 0.17337 0.17330 0.17322 0.17315 0.17308 0.17301 0.17294 0.17288 0.17281 0.17274 0.17266 0.17258 0.17249 0.17241 0.17233 0.17224 0.17215 0.17206 0.17196 0.17186 0.17176 0.17166 0.17156 0.17145 0.17134 85.26 85.51 85.76 85.89 86.01 86.26 86.51 86.76 87.01 87.26 87.SI 87.76 88.00 88.24 88.49 88.73 88.97 89.21 89.45 89.68 89.92 90.04 90.16 90.28 90.40 90.65 90.89 91.14 91.38 91.61 91.83 92.06 92.28 92.51 92.74 92.97 93.20 93.43 93.66 93.99 94.12 94.34 94.57 94.80 95.01 95.22 95.44 95.65 95.86 96.07 96.28 96.50 96.71 96.92 97.12 97.32 97.53 97.73 97.93 98.11 98.29 98.48 98.66 98.84 99.01 99.18 99.35 99.53 99.70 99.87 100.04 100.22 100.39 100.56 0.18547 0.18529 0.18511 0.18502 0.18494 0.18477 0.18460 0.18444 0.18429 0.18413 0.18397 0.18382 0.18369 0.18355 0.18342 0.18328 0.18315 0.18303 0.18291 0.18280 0.18268 0.18262 0.18256 0.18251 0.18245- 0.18235 0.18224 0.18214 0.18203 0.18193 0.18184 0.18174 0.18165 0.18155 0.18147 0.18139 0.18130 0.18122 0.18114 0.18106 0.13093 018091 0.18083 0.18075 0.18068 0.18061 0.18054 0.18047 0.18040 0.18033 0.18026 0.18018 0.18011 0J8004 0.17998 0.17993 0.17987 0.17982 0.17976 0.17969 0.17961 0.17954 0.17946 0.17939 0.17931 0.17922 0.17914 0.17906 0.17897 0.17889 0.17881 0.17873 0.17864 0.17856 Noth: Sp. En.' = Specific Enthalpy.