THE PASTEURIZATION OF MILK 



tube. The larger tube contains the water which 

 surrounds the small tubes which contain the milk. 

 When the regenerative principle referred to is em- 

 ployed, in this type of heater the hot milk return- 

 ing from the holding tanks is allowed to flow 

 through the larger tube, and thus assist in heating 

 the cold inflowing milk. 



Tubular heaters are doing very satisfactory 

 work. Those machines are in some respects the 

 most efficient in which the flow of milk is slow 

 enough or which have a sufficient heating surface 

 to insure that all portions of the milk will reach 

 the maximum temperature. It has been found 

 from experience that when milk flows through 

 tubes which are of comparatively large diameter, 

 there is a tendency for that portion of the milk 

 which is in the center of the tube to flow faster 

 than that which is close to the inner surface of 

 the tube. This is due to the greater friction at 

 the point of contact. It can be readily seen that 

 there will therefore be a tendency for the milk 

 which flows more slowly close to the heated surface 

 of the tube to become heated to a considerably 

 higher point than that near the center. When 

 the water entering the final tube of the heater is 



62 



