32 BULLETIN HI, U. S. DEPARTMENT OP AGRICULTURE. 



Consequently, if used for heating below the temperature of 212° F. 

 exhaust steam is practically as good as live steam. As the exhaust 

 steam when not used for heating is entirely lost, it is obvious that 

 by its use the efficiency of the plant will be greatly increased. 



Allowing for radiation from pipes, pasteurizers, hot-water tanks, 

 etc., it is safe to assume that 800 B. t. u. are available for useful 

 heating in each pound of exhaust steam. 



The exhaust steam available from the* engine, pumps, and other 

 steam-driven equipment, in milk plants, creameries, and dairies is, in 

 general, not quite sufficient to take care of the maximum heating load 

 which comes when pasteurizing is being done. But as the engine 

 and pumps are operated for some time, before pasteurization com- 

 mences, it is perfectly feasible to store up the heat contained in the 

 exhaust steam and draw on it when needed. 



Pasteurization is now done- almost entirely by the use of hot water, 

 the water being heated either in the jacket space included in the 

 construction of the pasteurizer or in a separate tank heater designed 

 for the purpose and pumped from the heater through the pasteurizer 

 and back into the heater. 



The ordinary feed-water heater found on the market is not suited 

 for use in milk plants except when it is used for heating the boiler 

 feed water only, as it has little or no storage capacity and the heating 

 surface is entirely inadequate. As hot water in dairy plants is used 

 intermittently it becomes necessary to provide a large storage ca- 

 pacity in order to have a- large quantity ready without delay when 

 needed. Storage heaters especially designed for creameries and milk 

 plants can be obtained from a number of manufacturers. 



In designing water heating and storage tanks for use in the dairy 

 industry the size should be based on the quantity and temperature 

 of the water required or on the quantity of exhaust steam available 

 for heating. In other words, the heat-transmitting surface should 

 be proportioned so that approximately all the heat available in the 

 exhaust steam will be transmitted to the water, provided, of course, 

 there is use for the hot water. 



Table 4 gives the capacity of water heating and storage tanks for 

 different-sized creameries, with the amount of heating surface neces- 

 sary to heat the water in each instance by exhaust steam at atmos- 

 pheric pressure and temperature, from an initial temperature of 50° 

 F. If) a final temperature of 200° F. in one hour. The heating sur- 

 face is supposed to be made up of steel or brass pipe. 



