Document 6wny6V5jJ2obppR09ejakzaR4

Heating Ventilating Air Conditioning Guide 1938 Table 5. Properties of Monofluorotrichlorombthane (Fn) Temp. F la per Sq In. liquid Vapor Hkat Content and Entropt Taken From --40 F Heat Content liquid Vapor Entropy liquid Vapor 25 F Superheat 50 F Superbeat Ht Ct Entropy Ht Ct. Entropy 0 2.59 0.01020 13.700 7.81 90.4 0.0178 0.1975 93.9 0.2049 97.4 0.2120 s 2.96 0.01024 12.100 8.81 91.2 0.0200 0:1974 94.7 0.2047 98.2 0.2117 10 3.38 0.01028 10.700 9.82 92.0 0.0222 0.1973 95.5 0.2045 99.0 0.2114 15 3.85 0.01032 9.530 10.80 92.8 0.0243 0.1971 96.3 0.2043 99.8 0.2111 20 4.36 0.01036 8.490 11.90 93.7 0.0264 0.1970 .97.2 0.2041 100.7 0.2109 25 4.94 0.01040 7.580 12.90 94.5 0.0286 0.1969 98.0 0.2039 101.5 0.2107 30 5.57 0.01045 6.770 13.90 95.3 0.0307 0.1969 98.8 O'. 2038 102.3 0.2105 35 6.27 0.01049 6.080 14.90 96.1 0.0328 0.1968 99.6 0.2037 103.1 0.2103 40 7.03 0.01053 5.460 16.00 96.8 0.0349 0.1968 100.3 0.2036 103.8 0.2101 45 7.88 0.01057 4.920 17.00 97.6 0.0370 0.1967 101.1 0.2035 104.6 0.2099 50 8.79 0.01062 4.440 18.10 98.4 0.0391 0.1967 101.9 0.2034 105.4 0.2098 55 9.80 0.01066 4.020 19.10 99.2 0.0412 0.1967 102.7 0.2033 106.2 0.2097 60 10.90 0.01071 3.640 20.20 100.0 0.0432 0.1967 103.5 0.2033 107.0 0.2096 65 12.10 0.01076 3.300 21.30 100.8 0.0453 0.1967 104.3 0.2032 107.8 0.2094 70 13.40 0.01081 3.000 22.40 101.5 0.0473 0.1967 105.0 0.2032 108.5 0.2093 75 14.80 0.01086 2.740 23.50 102.2 0.0493 0.1967 105.7 0.2031 109.2 0.2092 80 16.30 0.01091 2.500 24.50 102.9 0.0513 0.1966 106.4 0.2030 109.9 0.2090 85 17.90 0.01096 2.280 25.60 103.6 0.0533 0.1966 107.1 0.2029 110.6 0.2089 90 19.70 0.01101 2.090 26.70 104.4 0.0553 0.1966 107.9 0.2028 111.4 0.2088 95 21.60 0.01106 1.918 27.80 105.1 0.0573 0.1966 108.6 0.2028 112.1 0.2087 100 23.60 0.01111 1.761 28.90 105.7 0.0593 0.1965 109.2 0.2027 112.7 0.2085 105 25.90 0.01116 1.620 30.10 106.4 0.0613 0.1965 109.9 0.2026 113.4 0.2084 | S, S | As an example in the interpretation of the chart consider the case when moist air at a temperature of 80 F and a partial vapor pressure of 0.5 in. of mercury flows through a bed of silica gel which is at a temperature of 80 F. The chart indicates that the equilibrium of pressure between the air-vapor mixture and the bed is reached when the dry bed has adsorbed moisture to the extent of 31 per cent of the weight when dry. When this happens the bed can adsorb no more moisture unless its temperature is changed. In practice however the adsorbent bed is seldom held at a steady tem perature in air conditioning applications and neither is the adsorption process permitted to continue until moisture equilibrium is reached. Instead, the bed temperature varies and the bed-is re-activated before equilibrium is .approached. While charts of this kind can show the limiting properties of the substances they are seldom directly applicable to the solution of air conditioning problems unless considerable additional information is available. This takes the form of performance data cover ing the characteristics of the equipment in which the adsorbent bed, is placed. Such performance data are beyond the scope of this chapter. Liquid Absorbents Any absorbent substance may be used as an air drying agent if it has a vapor pressure lower than the vapor pressure in the air-vapor mixture from which the moisture is to be removed. Absorbents are character istically water solutions of materials in which the vapor pressure is 44 Chapter 2. Refrigerants and Air Drying Agents reduced to a suitable level by governing the concentration of the solution. In addition to having a,suitable low vapor pressure, a practical absorbent must also be widely available at economical cost, be non-corrosive, odorless, non-toxic, chemically inert against any impurities in the air stream, stable over the range of use and especially it must not precipitate out at the lowest temperature to which the apparatus is exposed. It must have low viscosity and be capable of being economically regenerated or concentrated after having been diluted by absorbing moisture. Water solutions, or brines, of the chlorides of various inorganic elements such as calcium chloride and lithium chloride are the absorbents most frequently used in connection with air conditioning applications and de tailed attention is confined to these two in this chapter. Nature of Absorption Process The application consists of bringing the air-vapor stream into intimate contact with the absorbent, permissably by passing the air stream through a finely divided spray of the brine but more generally by passing the air over a metal surface coil where the liquid absorbent presents a large surface to the air stream. The difference in vapor pressures causes some of the vapor in the air-vapor mixture to migrate into the brine. Here it condenses into liquid water and decreases the concentration of the absorbent. In order that the process be continuous means must be provided for counteracting the diluting effect of the extracted moisture and also for maintaining the temperature of the brine sufficiently low to hold the desired vapor pressure. As the water vapor is added to the absorbent and condenses, it gives up its latent heat of condensation which tends to raise the temperature of both the absorbent and the moist air stream. For every pound of water absorbed and condensed the heat added to the air stream and the brine Table 5. Properties of Water Temp. F Press. Lb per Sq In. liquid Vapor Heat Content and Entropt Taken From +32 F Heat Content Entropy 50 F Superheat 100 F Superheat liquid Vapor liquid Vapor Ht. Ct. Entropy Ht Ct. Entropy 32 0.0887 0.01602 3296.0 0.00 1073.0 0.0000 2.1826 1096.9 2.2277 1120.8 2.2688 35 0.1000 0.01602 2941.0 3.02 1074.4 0.0062 2.1724 1098.3 2.2172 1122.2 2.2581 40 0.1217 0.01602 2441.0 8.05 1076.8 0.0163 2.1555 1100.6 2.2000 1124.5 2.2406 45 0.1475 0.01602 2034.0 13.07 1079.2 0.0262 2.1390 1102.9 2.1832 1126.7 2.2234 50 0.1780 0.01602 1702.0 18.08 1081.5 0.0361 2.1230 1105.2 2.1667 1129.0 2.2066 55 0.2140 0.01603 1430.0 23.08 1083.9 0.0459 2.1073 1107.5 2.1506 1131.3 2.1902 60 0.2561 0.01603 1206.0 28.08 1086.2 0.0556 2.0920 1109.8 2.1349 1133.5 2.1742 65 0.3054 0.01604 1021.0 33.08 1088.6 0.0652 2.0771 1112.2 2.1196 1135.8 2.1585 70 0.3628 0.01605 868.0 38.07 1090.9 0.0746 2.0625 1114.5 2.1046 1138.1 2.1432 75 0.4295 0.01606 740.0 43.06 1093.2 0.0840 2.0483 1116.7 2.0900 1140.3 2.1283 80 0.507 0.01607 632.9 48.05 1095.5 0.0933 2.0344 1119.0 2.0758 1142.5 2.1138 85 0.596 0.01609 543.3 53.04 1097.8 0.1025 2.0208 1121.2 2.0619 1144.7 2.0996 90 0.698 0.01610 467.9 58.03 1100.0 0.1116 2.0075 1123.4 2.0483 1146.8 2.0857 95 0.815 0.01612 404.2 63.01 1102.3 0.1206 1.9946 1125.6 2.0350 1148.9 2.0721 100 0.949 0.01613 350.3 68.00 1104.6 0.1296 1.9819 1127.9 2.0220 1151.1 2.0588 105 1.101 0.01615 304.4 72.98 1106.8 0.1384 1.9695 1130.2 2.0093 1153.2 2.0458 For properties of steam at high temperatures, see Page 28. 45