THE SPRAY PROCESS 313 



The arrangement of the exit of the moisture-laden, spent air 

 also differs with different drying chambers. In many cases, espe- 

 cially where the heated air and spray enter at one side, the exit 

 of the moisture-laden air is on one side, in this case on the side 

 opposite that of the intake. In other cases the spent air escapes 

 at the top and in still others near the bottom of the desiccating 

 chamber. 



Hausbrand 1 points out that the air always enters the desic- 

 cating room hotter than it leaves and that the spent air is usually 

 more completely moisture-saturated than the incoming air. The 

 density of the spent air therefore is greater than that of the air 

 at the intake. The spent air is heavier. It has, consequently, an 

 inclination to pass downward. Hausbrand accordingly holds, that 

 in vertical drying rooms the direction of the currents of air should 

 be from top to bottom, since the movement is then more uniform 

 than when the heated air enters below and at once takes the shortest 

 path to the upper exit, without coming in contact with all the dry- 

 ing material. 



It is important that the drying room be protected against 

 the entry of air from outside. The walls must be free from leaks, 

 the peep holes or sight glasses, the doors and the shutters in the 

 hopper at the bottom, must fit tightly. 



The outgoing air, in a properly operating desiccating cham- 

 ber, should have a temperature considerably lower than the incom- 

 ing air. As previously stated, it usually is, and it is desirable that 

 it should be below 200 F., and preferably not above about 150 F. 

 The lowering of the temperature of the heated air in the desiccat- 

 ing chamber is due to the cooling effected by the rapid evaporation 

 of the moisture from the spray of milk. This cooling effect in 

 turn protects the milk solids against changes resulting from contact 

 with the hot air, and assists in preserving their .original solubility. 



Recovery of Desiccated Milk. Because of the extreme fine- 

 ness and lightness of the milk powder made by the spray process 

 of desiccating milk, a certain portion of the most flaky and fluffy 

 particles escapes from the desiccating chamber with the outgoing 

 air. As previously stated, the proportion of powder that thus 

 escapes varies greatly with the degree of flakiness or granulation 



1 Hausbrand, Drying by Means of Air and Steam, 1901. 



