310 THE SPRAY PROCESS 



Most of these chambers are rectangular, measure from about 

 12 feet in length, width and height upward to much larger dimen- 

 sions. Some are longer than they are wide and others are much 

 higher than they are wide and long. Still others are of the circu- 

 lar type, resembling small silos, and some are cone-shape. 



The desiccating chambers are usually completely lined with 

 tin plate on the inside, making them air tight or nearly so. In 

 order to prevent waste of heat by radiation through the walls, top 

 and bottom, they must be properly insulated. This is generally 

 done with asbestos sheeting. 



Spray Nozzles. The milk enters the desiccating chamber 

 through one or more spray nozzles, under a pressurfc of about 

 3,000 pounds. The spray nozzles are generally located in the side 

 of the drying chamber in close proximity to the top, so as to give 

 the spray particles as far a distance to fall through the heated air 

 as the height of the chamber permits. Or the spray nozzle may be 

 located in or near the center of the drying chamber, in its upper 

 portion, in which case the spray issues outward radially, or is blown 

 out of the nozzle tangentially by giving the spray nozzle a rotary 

 motion. 



When more than one spray nozzle is used, the multiple noz- 

 zles are either arranged in a straight row along one side, or they 

 may be distributed over two or over all four sides of the desic- 

 cating chamber. 



Different types of spray nozzles or atomizers are used. In 

 some hot air under pressure, or steam, propels and blows the milk 

 through the nozzle on a similar principle as the boiler water in- 

 jector. In other cases the spray nozzle consists of a heavy black 

 iron cap, about one and one-quarter inch long and with a one-half 

 inch threaded bore. This cap is screwed on to the end of the 

 milk pipe, or its laterals. In the center of the closed end, the cap 

 has a very fine opening with a diameter of from one-half to one 

 millimeter (.02 to .04 inch). A small brass disc, about one-quar- 

 ter inch thick and snugly fitting into the iron cap, lays against 

 the closed end of the cap and covers the small orifice. This brass 

 disc carries two minute spiral grooves at its periphery, through 

 which the milk under pressure is forced between disc and cap 



