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616 - CHAPTER 38 1948 Guide may'Jje obseryed,by'refemng. tp Fig: 1- When the given, type of solid adsorbent' is. in equilibrium with. air'having a dry-bulb' ^temperature 'of 70 F and;.7P per cent relative humidity, that is, having`a.dew-point of 60 F or d'water'vapor pressure,of 13.2 mm Hg, the 'water,content'of the' ' adsorbent is 33 per cent,- 'With air having'the same dry-bulb temperature' and a dew-point of 37 F,or a vapor pressure of. 5.6 mm Hg, the water content is 20 per cent. The increase, in weight for , an activated solid adsorbent after it reaches equilibrium with a gas of any giveri water vapor;: content, may bp found , by subtracting the residual water content (for example 6 per cent) from the equilibrium value. In the case of the, two examples cited,: the actual water gain would be 27 per cent and 14 per cent respectively. ; The Effect, of temperature upon the adsorptive Fig. 1. Temperature--Vapor Pressure --Concentration Characteristics for a Typical Solid Adsorbent Fig. 2. A Typical Solid Adsorbent. Dehumidification Unit Air . . Flow Diagram capacity may be observed by following the 5.6 mm Hg vapior pressure line. At a temperature of 70 F the moisture content of the adsorbent is 20 per cent, while at 100 F the equilibrium water content is 11 pier cent. In practice the temperature rise in the dehumidified air caused by the adsorption heat is approximately 10 deg F for each grain of moisture removed pier cubic foot of air at atmospheric, pressure. This, temperature rise occurs progressively through the adsorbent bed and is an important, consideration in predetermining the-performance of a given design of apparatus. Data such as these, together with information covering other characteristics such as specific heat, resistance to air flow, etc., are of value in the basic design of adsorption apparatus. In the solution of air conditioning problems, however, reference must be made to per formance data on established apparatus-designs. DehuniidificatUm by Sorbent Materials 677 DEHUMIDIFICATION EQUIPMENT USING SOLID ABSORBENTS - `A' typical 'solid adsorbent dehumidification' unit ait flow diagram is shown' in Fig. 2. The apparatus' consists of tiwo adsorbent Containers (adsorbers) with necessary interconnecting piping, valves,, and.auxiliaries consisting of filters; fans, activation air heater, controls, and in some instances a cooler for the' dehumidified air. Before entering the adsorber the air to be dehumidified is drawn into a filter to remove dust and other impurities. In passing through the adsorbent bed-; the moisture content of the.air is reduced and the dehumidified air is then introduced into the space or. process `requiring it. While the first adsorber, is dehumidifying the air, the second adsorber is being reactivated by means of outside air drawn through ,a filter and heater, in which its: temperature is raised , to 300 F. The heat may^be supplied by electric heating elements, steam coils, the direct products of combustion of gas, oil, waste heat, or any other convenient source. In passing through the adsorbent bed, the hot gases supply the necessary heat for.releasing adsorbed water from the adsorbent and then carry it out of the adsorber to the activation gas outlet, where it is. exhausted to the outside atmosphere. In some in stances a thermostat placed in the, activation outlet connection shuts off the activation fan and heater when the adsorbent is completely reacti vated, as indicated by a rapid rise in the temperature of the outlet activation gas. - The length of the adsorption pieriod may be, controlled by a timing device which changes the valves or dampers' from the ad sorbing to. the activating position, or, by a humidistat located in the dehumidified air connection or in the dehumidified space. The. majority of commercial Units are time controlled1 In applications where a continuous stream of dehumidified air is not required; a single adsorber type unit may be used, while in other cases where a continuous stream of dehumidified air is required/a multiplenumber of adsorbers or even a continuously rotating system may be used. .If the air to be dehumidified is very warm, and especially where exceedingly-low dew-point dehumidified air is required, it is advantageous to install a pre-cooler to reduce the temperature of the inlet air. In this way the working temperature in the adsorber is lowered and the over-all performance appreciably increased. Some equipment, manufacturers, install cooling coils in the adsorbent beds for the same purpose, while others divide the adsorbent bed and install coolers between the sections.- Dehumidification equipment is employed to the best advantage where the air conditioning problem is primarily one of obtaining low relative humidity control rather than temperature control. This requirement is found in the case of the preservation of inactive naval vessels where the interior of the ship must be kept at a relative humidity below 30 pier cent to avoid corrosion, mold, mildew, and other moisture damage that occurs at humidities substantially in excess of this figure. Other advan tageous applications for dehumidification systems are found in industrial processes where, low relative humidity atmospheres are required during the manufacture as well as for preservation of the finished products. Dehumidification with cooling may be used to advantage in work-rooms or other spaces occupied by humans, where the moisture load is high in comparison to the sensible heat load. In many instances where inde pendent control of temperature and humidity is important dehumidification is used to advantage in conjunction with cooling.