Document Z4kG5q5LRVdaaEa4VXzb424op

HEATING VENTILATING AIR CONDITIONING GUIDE 1944 so. luEtxioanmsp. le . Determine the boiling point, and freezing point of 18 M lithium chloride Solution. From Table 1, boiling point, (standard) is 285.8 F, freezing point is 58.1 F. Example S. Calculate the heat of vaporization of 1 lb of water from a large amount of 18 M lithium chloride solution at the boiling point. Solution. The heat of boiling is equal to the heat of mixing plus the heat of boiling pure water at the same temperature. The heat of mixing from Table 1 at 18 M and 285.8 F is 145 -- (0.186 X 285.8) = 92 Btu per pound. The heat of vaporization of water from steam tables at 285.8 F is 920 Btu per pound. Therefore the heat of vaporiza tion of water from the solution is 920 + 92 = 1012 Btu per pound. Example 4. One thousand pounds of air per minute at 100 F dry-bulb with a dew point of 70 F and a relative humidity of 39 per cent are passed over 18 Mlithium chloride solution. The rate of flow of the solution is 200 gpm and the entering temperature is 80 F. The air leaves the absorber at 85 F dry-bulb and dew-point of 35 F. Calculate (a) the heat to be removed from the lithium chloride solutioh to maintain these con ditions, and (6) the temperature rise of the solution in. passing through the absorber. Solution, (a) The enthalpy of the entering air at 100 F dry-bulb and 39 per cent relative humidity = Aa + i*Aaa = 24.00 + (0.39 X 47.40) = 42.49 Btu per pound (Table 6, Chapter 1). The relative humidity of the air leaving at 85 F dry-bulb and 35 F dew-point is 16.7 per cent (psychrometric chart). Enthalpy of leaving air = 20.39 + (0.167- X 28.85) -- 25.21 Btu per pound (Table 6, Chapter 1). : Heat to be extracted from air -- 1000 (42.49 -- 25.21) = 17,280 Btu per minute: Heat of mixing = 145 -- (0.186 X 80) 1 130 Btu per pound of moisture removed. From Table 6, Chapter 1, the moisture removal per pound of air = 0.01574 -- 0.00426 = 0.01148 lb. Heat of mixing for 1000 lb of air = 1000 X 0.01148 X 130 = 1492 Btu. Total heat extraction = 17,280 + 1492 = 18,772 Btu per minute. (i) The weight of solution circulated is 200 X 1.27 (Table 1) X 8.33 = 2116 lb per minute. Its heat capacity = 2116 X 0.631 (Table 1) = 1335 Btu per minute per degree Fahrenheit. The temperature rise = 18,772 H- 1335 = 14.1 F. SOLID DEHYDRATION METHODS One type of equipment suitable for producing dehydration with solid drying agents utilizes an apparatus with continuous operating rotating beds or dampers as illustrated in Fig. 4. The apparatus consists.essen tially of a cylinder or drum filled with dehydrating material. Air flow 454 CHAPTER 24. COOLING, DEHUMIDIFICATION AND DEHYDRATION ' through the drum is directed by baffles which permit three independent air streams to flow through the adsorbing .material. One air stream con sists of the wet air which is to be dehydrated. The second is heated activation air used for drying that part of the dehydrating material which has become saturated. The third air stream cools the bed to a tem perature below 150 F to permit pickup of moisture when that part of the bed returns to the dehydration cycle. In the rotating bed apparatus, the baffle sheets are stationary and the screened bed rotates at a definite speed to permit the proper time of contact in the activation, cooling and dehydration cycles. In the rotating Table 3. Density of Lithium Chloride Solutions Concentration (42.4 lb) Lid per 1000 lb Water 6 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 0 * so 1.090 1.124 1.156 1.188 1.217 1.242'. l 1.045 1.085 1.119 1.150 1.181 1.209 1.235 1.257 1.279 Temperature Deo F 100 ISO 200 250 1.037 1.076 1.111 1.143 1.172 1.199 1.225 1.248 1.270 1.291 1.026 1.064 1.100 1.132 1.162 1.188 1.214 1.236 1.259 1.280 1.310 1.317 1.012 1.052 1.087 1.122 1.152 1.178 1.203 1.226 1.248 1.279 1.289 1.307 1.313 1.338 1.142 1.168 1.192 .1.215 1.237 1.568 1.278 1.296 1.312 1.327 1.34 300 1.267 1.286 1.302 1.318 1.33 1.35 damper apparatus, the bed remains stationary and a sectionalized damper rotates. This rotating damper produces the same general effect as if the stationary baffles previously mentioned rotated. Clean air for activation is supplied at temperatures normally ranging t) from 300 to 350 F. Any source of clean heated air can be used such as air heated by electric -heaters or steam coils, or air indirectly heated by coal or oil fired interchangers. Direct fired heaters are usually designed for gas since there must be no condensable tarry combustion products to-contaminate the adsorbent. To avoid excessive contamination or clog ging of the absorbent bed by dust it is frequently desirable to provide filters for the activation air. Where activation air heating coils are supplied with steam at 80 lb per square inch gage pressure or higher, activation efficiency will remain normal and moisture removal capacity will not be reduced. When lower steam pressures are used, incomplete reactivation will result in reduced moisture removal. ......... :r:; 455