2 1 PASTE URIZ ATION 



Under the regenerative principle the cold cream is heated 

 by the hot cream passing from the pasteurizer. In the outflow, 

 hot cream is cooled by the cold cream flowing into the pas- 

 teurizer. The hot and cold cream then equalize their respective 

 temperatures by passing in different directions. It is claimed by 

 manufacturers of these pasteurizers that they effect a saving of 

 25 per cent, or more. 



Most pasteurizers at the present time are constructed of 

 heavy copper coated with tin. The heating surface of some of 

 these pasteurizers is lined with German silver. From the stand- 

 point of heat conductivity there is little choice between these two 

 metals. It is a well-known fact that some metals will conduct 

 heat better than others; the relative heat conductivities of 

 copper and tin are .918 and .145 respectively. This means that 

 copper will conduct heat nearly seven times as fast as tin of the 

 same thickness, and therefore that copper might be seven times 

 as thick as tin and still transmit as much heat as the tin. From 

 this it can be seen that a heating wall made from copper can be 

 increased slightly in thickness, and thus aid in stability, without 

 affecting the degree of heat conductivity of the wall very much. 

 The heating surface must be strong enough to withstand a 

 slight steam pressure, otherwise the heating wall is likely to 

 collapse or cave in, in case of slight variation in the steam pressure. 

 It used to be a rather common occurrence for the heating walls of 

 the pasteurizer to cave in or collapse in case of a slight variation 

 in the steam pressure. This does not happen so often now. 



The condition of the cream has some bearing on the heating 

 surface. Sour and coagulated cream burns and adheres to a 

 greater extent than does sweet cream. This is evidently due to 

 the lesser fluidity of the sour cream. Where two pasteurizers 

 are used, this tendency is overcome to a very large extent. 



Efficiency of Pasteurizers. Experiments conducted by Dr. 

 Storch of the Royal Experiment Station, Copenhagen, Denmark, 

 show that condensed steam offers great resistance to the trans- 

 mission of heat. The comparative heat conductivities of water 

 and copper are .0016 and .9 respectively, as found by Dr. Storch. 

 It will thus be seen that copper is 600 times as good a conductor 



