HUMIDITY-REGULATED AND RECIRCULATING DRY KILN. 23 



GENERALIZATION. 



A study of the theoretical heat relations, as shown by Hausbrand's 

 tables, makes possible the following generalizations: 



1. With tg constant and entering air saturated, the expenditure of 

 heat is less, the higher the temperature, t^, of the entering air. 



2. With ti constant, the expenditure of heat is less, the higher the 

 temperature, tj, to which the air is heated. 



3. Other things being the same, the heat expenditure increases 

 rapidly with reduction in humidity of the emergent air. 



4. Other things being the same, the heat expenditure is less, the 

 lower the humidity of the entering air. 



5. Other things being the same, the expenditure of heat increases 

 with increase of pressure. 



6. With water vapor in the absence of air, the theoretical efficiency 

 becomes 100 per cent. 



In regard to the weights and volumes of air required, the following 

 observations are obtained, with entering air saturated : 



With ta constant, both the weights and volumes of air required to 

 evaporate 1 pound of water increases with increase of the initial 

 temperature, t^, of the entering air. 



With ti constant, both weights and volumes decrease with increased 

 temperature, tj, of the heated air. 



With the emergent air only partially saturated, the weights and 

 volumes increase with decrease of relative humidity in the emergent 

 air. 



CONCLUSIONS AS TO EFFICIENCY OF OPERATION. 



From this analysis of the heat equations the following conclusions 

 as regards the efficiency of the drying may be drawn : ^ 



1. The air should be heated to the highest temperature compatible 

 with the nature of the material to be dried. 



2. The air upon leaving the apparatus should be as near saturation 

 as practicable. 



3. The temperature of the entering air should be as high as 

 possible. 



APPLICATION OF ANALYSIS TO THE WATER SPRAY OR CONDENSING KILNS. 



The above deductions apply to any form of moist-air kiln. The fol- 

 lowing have more especially to do with the Forest Service water 

 spray humidity regulated kiln. 



The amount of heat absorbed by the spray water and the con- 

 densed moisture aside from losses through the kiln walls is the 



1 It should be noted, as stated above, that these deductions apply solely to the evapo- 

 rating process alone, from a theoretical standpoint, and do not take into consideration 

 heat losses through the kiln walls or through extraneous conditions ; nor do they signify 

 what is the condition best suited for conducting the drying operation from the stand- 

 point of the physical effect upon the wood. 



