Document g2GX36E0w1x4D3GbQ9zqDgwaL

American Society 0/ Heating and Ventilating Engineers Guide, 1937 air up to about 8 or 10 per cent of the weight of the adsorbing material* after which the adsorption falls off gradually as the saturation pointy approached. The application is quite similar to that employed for siljJ gel; that is, the material is exposed to the air flow and after reachiJ about 75 per cent saturation is reactivated by removing the moist^ adsorbed by means of applied heat. The actual scheme generally fol lowed in the use of this material for continuous service varies somewhat! tfr__o_ _m_____s:iil:ic__a____g__e_ 1l :in___a__s__m___u___c_1h____a__s4-1t_h__e____m___a_ :t_e___r_i_a___l__i_s___p_ 1la----c---e---d-1 in 4t.h1---r--e---e-- ---u----n- -i--t--s-----w----hli-ch. used consecutively for the different steps, These steps permit each to operate as follows: a. In series with the preceding unit. b. Alone. m e. In series with the following unit. This plan allows for adsorption, reactivation, and cooling, in a manner! similar to that used with silica gel. ' Taking a single unit, when it is in the a step and operating with the preceding unit, the alumina adsorbs approximately 25 per cent of the moisture in the air and takes up about 1.3 per cent of its weight of water. During the second step when it is operating alone, it takes up 100 per cent of the moisture in the air until the weight of the water adsorbed is brought H up to about 6.7 per cent. During the third step when the unit is operating with the succeeding unit, it extracts about 75 per cent of the moisture in the air until the water weight adsorbed comes up to about 10 per cent of the weight of the adsorber. The time allowable for reactivating is equal to the time occupied by the second unit adsorbing alone, plus the time when the second and third units are adsorbing in series, plus the timgj when the third unit is adsorbing alone, at the expiration of which time thef first unit will be again required. The temperature of air used for alumina reactivation is usually between 300 and 700 F and the air flow rate will have to be higher with the low temperature air than it will be with reactivating air of higher temperature. For example, air at 400 F for reactivating will, at 10 cu ft pier hour per pound of alumina, require about 6 hours for reactivation. In the three unit system, after reactivation the cooling of the activated alumina may be carried out with considerable rapidity by using dry air from the adsorp-1 tion unit for circulation through the unit which has just completed reacti-1 vation. The final temperature of the unit before it goes back into service should be not over 200 F. As a basis for computing the amount of cooling air required for reactivation, each cubic foot of cooling air has been found ] capable of removing 2.2 Btu when heated from 85 to 200 F and of provid ing a sufficient margin of safety in operation. Lithium Chloride Adsorption System Practically all salt solutions have the property of adsorbing or con- !j densing moisture from a gas. The amount depends on the character of l the solution, its gravity, temperature and viscosity. One of the best ' known dehydraters, calcium chloride, for instance, has been long known for this property. Its characteristics, however, present a limiting factor of about 30 per cent relative humidity, so that the resultant dew point of air brought in intimate contact with calcium chloride is usually too high for comfort work without further refrigeration. 200 The cycle of solid dehydraters or adsorbere and liquid adsorbers are fundamentally the same. A diagram of- a lithium chloride adsorption sysTtheme liisqsuhidowandisnorFbiegr. i1s. b.rought in contact with air having a certain vapor pressure due to the moisture of water vapor that is in it, and the chloride, either sodium, lithium, calcium, or whatever is used, having a lower vapor pressure, adsorbs moisture in the form of water from the water vapor that is in the contacting air. Thermodynamically, it is definitely possible to measure this change and to know definitely that a change of state takes place because of the fact that there is a definite rise - ipmnerature in the liquid adsorbing the moisture, which is definitely a fV,o air cif-fpam Conditioned air 201 /