Document M461Lzeav0oRG65G9mE6wK4bM

American Society of Heating and Ventilating Engineers Guide, 1935^ Chapter 10--Cooling Methods refrigerant, and a compressor is employed to withdraw enough |rJ pressure saturated gas to keep the cooling action of the evaporator nJ tinuous. The withdrawn gas is discharged from the compressor to (d I condenser in the form of a high-pressure superheated gas which inclu^ * the heat added through its compression. In the condenser, because 1 6 is taken from the gaseous refrigerant by the condensing medium, usualli water, the refrigerant again becomes the high-pressure saturated liqtS with which the cycle started. ^ The cooling water, which may come from a deep well or from a ciS main, may be utilized for some purpose after it has been warmed a degrees in the condenser, or after use it may be exposed to the atmosphef rMcrical Application of Silica Gel - ..... , jjas two applications when used to replace refrigeration. In Silica ge . jjy used, the air from which moisture is to be extracted is tHe one pri gej y,ec}s by suction or pressure fans, and by means of taken tor0 m0;sture becomes adsorbed by the silica gel and the air this Prce jower jew point and a higher sensible temperature than those leaves a ^ enterecj. If this air is passed over surface coolers in which tap at whic i coojjng medium is flowing through tubes, a certain water o sensj^,[e heat will be removed. The air leaves the surface cooler amqun an er with the same dew point with which it emerged from the T*n eel beds, but with a lower dry-bulb temperature, although the dry- bulb temperature may be higher than the temperature of the air entering the silica gel beds. In another method, the first two of the steps outlined are duplicated, nd in addition the air is carried through a spray type washer. Because the air enters the washer with a low wet-bulb, and because adiabatic saturation will take place at a temperature close to the entering wet-bulb, considerable cooling of the air can be accomplished; but this can be done only with a consequent increase of the dew point. It is necessary to reactivate the silica gel after it has adsorbed about 25`per cent of its own weight in the form of moisture. As reactivation requires a high temperature and since silica gel is only active at low tem peratures, cooling of the beds must also be completed before they can be used again. This necessitates three stages in the silica gel containers and requires either three beds of silica gel or one bed divided and automatically put in position. The reactivation is usually done by means of gas or oil fires and the cooling of the beds by means of indirect water cooling or by . means of small quantities of dehydrated air taken from the system beyond , the interchanger. Fig. 2. Silica Gel Air-Conditioning System--Single Stage Adsorption Alumina System of Adsorption in a spray pond or cooling tower and Have its temperature reduced to? point where the water may be used again. (See Chapter 11.) Activated alumina contains a trifle over 91 per cent of aluminum oxide, AkQi, which material will adsorb nearly 100 per cent of the vapor in the air.up to about 8 or 10 per cent of the weight of the adsorbing material, Silica Gel System Silica gel is a chemical composition made from sodium silicate and add, the chemical formula being Si02. It has an appearance greatly resembles that of clear quartz sand but it differs in structure in that the crystals are highly porous, with voids constituting 41 per cent by volume although the pores are microscopic in size. This material possesses the property'^ being able to adsorb a substantial portion (about 25 per cent of its oira weight) of moisture from the air without any increase in its volume After the silica gel has become "saturated" or has adsorbed moisture^ . after-which the adsorption falls off gradually as the saturation point is approached. The application is quite similar to that employed for silica : gel; that is, the material is exposed to the air flow and after reaching about 75 per cent saturation is reactivated by removing the moisture J&gjgbfd by means of applied heat. The actual scheme generally fol lowed in the use of this material for continuous service varies somewhat 'frontsilica gel inasmuch as the material is placed in three units which are ' used consecutively for the different steps. These steps permit each unit to operate as follows: the limit of its capacity, the moisture may be driven from it by tig application of heat, again without change in the structure, volume, '.? series with the preceding unit. 6.A]one chemical composition of the silica gel. This cycle may be repeated ij| |. -,'f. In senes with the following unit. definitely. When applied to air conditioning the silica gel which g exposed to the air reduces the moisture content in the air and release, sensible heat which may be readily removed from the air. A typidjj diagram is shown in Fig. 2. ,,vThis plan allows for adsorption, reactivation, and cooling, in a manner similar to that used with silica gel. TakinS a single unit, when it is in the a step and operating with the 1GS 169