Continuous Process Evaporators 139 



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 



2500 

 in a 3 feet diameter machine must revolve . - , . = 265 times 



3x3.14 



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



2500 

 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 of 

 the continuous concentrator is simple and the ratio of concentra- 

 tion 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 m.ilk is subjected in the concentrator. 

 Any method of forewarming or preheating may be used for this 

 "purpose, but since the milk flows to and through the concen- 

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

 warmer of the continuous type. The milk should be heated to 

 about 185 to 200° 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 st«amed, 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 

 so as to avoid the blades from running over t'he dry heating sur- 

 face, cutting the copper. Simultaneously with the starting of the 



