Document M4Zx616kXjaM0e5205eB32mNy

HEATING VENTILATING AIR CONDITIONING GUIDE 1940 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 Table 7. Dew-Point of Air in Equilibrium with Lithium Chloride Solutions Concentration in Pound Mols (42.4 lb) Lithium Chloride per 1000 lb Water DswPoint at Zero Co*0- 2,, 4.0 6.0 8.0 Concentration or Lithium Chloride 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 320315.2 308.7 299.9 290.2 279.7 269.4 259.6 251.5 244.1 236.5 230.0 223.8 218.6 214.5 210.3 300295.4 289.1 280.5 270.9 260.6 250.5 240.8 232.6 225.4 218.0211.8 205.8 200.8 196.9 192.8 280275.6 269.5 261.1 251.7 241.5 231.6 222.2 214.0 206.7 199.7 193.5 187.8 183.2 179-3 175.2 260255.8 250.0 241.9 232.6 222.7 212.8 203.5 195.5 188.4 181.7 175.4 170.0 165.6 162.0 158.4 240236.0 230.4 222.5 213.5 203.8 194.2 185.0 177.1 170.0 163.6 157.5 152.2 148.3 144.6 140.5 220216.2 210.8 203.2 194.4 184.9 175.5 166.4 158.6 151.6 145.3 139.6 134.6 130.7 127-3 124.2 200196.4 191.2 183.9 175.4 166.1 156.7 148.0 140.3 133.5 127.3 121.9 117.0 113.3 110.1 180176.6 171.6 164.7 156.4 147.3 138.1 129.6 122.1 115.5 109.4 104.2 99.6 96.0 160.156.8 152.1 145.4 137.4; 128.6 119.7 111.3 103.9 97.4 91.6 86.6 82.2 140137.0 132.6 126.1 118.4 109.9 101.3 93.1 85.9 79.5 73.8 69.0 120117.2 113.0 106.8 99.4 91.1 82.7 74.7 67.8 61.5 56.0 110,107.3 103.2 97.2 89.9 81.9 73.5 65.6 58.8 52.6 47.1 lOffi 97.4 93.4 87.5 80.5 72.7 64.4 56.6 49.8 43.7 38.2 90 87.5 83.6 77.9 71.0 63.3 55.2 47.6 40.8 34.8 29.3 80 77.6 73.8 68.4 61.6 54.0 46.1 38.5 31.8 25.9 20.6 70 67.7 64.0 58.7 52.2 44.8 37.0 29.5 22.9 17.2 12.0 60 57.8 54.3 49.1 42.7 35.5 27.9 20.5 14.0 8.3 40 38.0 34.7 29.9 23.9 16.9 9.6 2.4 -3.9 320 15.1 10.7 5.0 -1.7 -8.7 -15.4 -4.5 -8.6 -13.9 -20.2 -27.0 -33.3 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 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, 40 CHAPTER 2. REFRIGERANTS AND AIR DRYING AGENTS 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. Fig. 2. Temperature--Pressure--Concentrations for Lithium Chloride 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 41 LOG VAPOR PRESSURE, MM. HG.