' CONTINUOUS PROCESS EVAPORATORS 173 



Speed of Agitator. ^The proper speed of the continuous 

 concentrator is expressed in terms of rim speed, that is the 

 distance which the blades travel per minute. It has been found 

 that the rim speed which is sufficient to move the film of milk 

 in the machine properly, is about 2500 feet per minute. In order 

 to insure a rim speed of 2500 feet per minute, the blades in -a 3, 



2500 



foot diameter machine must revolve 265 times per 



3x3.14 



minute. In a six foot diameter wheel, the same rim speed would 



require "* . 133 revolutions per minute of the spider. 

 6x3.14 



Again, it has been found that the blades should be not more 

 than about 2\ feet apart. A three foot diameter concentrator, 

 therefore, requires four blades while concentrators with larger 

 diameter require a larger number of blades in order to keep the 

 distance between blades within the limit of two and one-half 

 feet. 



Operation of Continuous Concentrator. The operation oi 

 the continuous concentrator is simple and the ratio of concen- 

 tration of the product can be regulated as desired. 



Heating of Milk. Similar as in .case of evaporation in 

 vacuo, it is desirable, if not necessary, to heat the milk before 

 it enters the concentrator. This not only increases the capacity 

 of the machine, but it also prepares the casein in the milk for 

 the superheating to which the milk is subjected in the concen- 

 trator. Any method of forewarming or preheating may be used 

 for this purpose, but since the milk flows to and through the 

 concentrator, in a continuous stream, it-is preferable to also use 

 a forewarmer of the continuous type. The milk should be heated 

 to about 185 to 200 degrees F. and the forewarming' should be 

 so arranged that the milk is exposed to this temperature for 5 

 to 10 minutes before it enters the concentrator. 



Condensing. -The concentrator is steamed, the parts of. the 

 agitator are assembled and installed in their proper place, the 

 cover is securely bolted over the opening in the front head and 

 the machine is ready for operation. Before starting the agitator 

 a small amount of milk is permitted to flow into the concentrator 



