THE COST OF PASTEURIZING MILK AND CREAM. 
5 
the milk entering the heater is thus heated, while that entering the 
cooler is partly cooled, the cooler proper reducing the temperature 
to the point desired. The function of the regenerator is therefore 
to economize heat by transferring the heat from the hot to the cold 
milk. The hot milk coming from the heater flows into the holding 
vat and is here held for about 30 minutes. It then flows through 
the regenerator to the cooler, where it is cooled by water and brine 
circulation, direct expansion of ammonia in the cooler pipes some- 
times being used instead of brine. 
Just the reverse is true in the case of the cold milk; that is, the cold 
milk comes from the receiving vat, where it is at a temperature of 
about 55° F., and goes through the outer coils of the regenerator, 
where it is heated by the returning hot milk. It is obvious, therefore, 
that any heat transferred from the hot to the cold milk represents 
just so much gain in economy. If it were possible to transfer all the 
heat in the hot milk above the initial temperature of the raw to the 
cold incoming milk after the first charge had been once heated to 
the pasteurizing temperature, the heater could be dispensed with 
entirely, and the pasteurizing would go on indefinitely. This would 
constitute, however, a theoretically perfect machine, which is an 
impossibility; but the more perfect the regenerative apparatus the 
less heat will have to be supplied by the heater. The heat balance 
in test No. 5 shows that it would have taken over two and a half 
times the heat had no regenerator been used. 
In all of the foregoing tests the pasteurizing was done with live 
steam taken direct from the boiler but reduced in pressure to from 
3 to 5 pounds. Subsequent tests show that the pasteurization could 
just as well have been done with exhaust steam, and by so doing a 
load of from 8.75 to 24.8 boiler horsepower could have been taken off 
the boiler plant except in plant 1, where the exhaust steam was 
utilized for making ice in an absorption ice plant. 
Attention is invited to the saving obtained by the use of regenera- 
tors in the foregoing tests. The boiler horsepower per hour required 
for pasteurizing in tests Nos. 1, 2, 3, 4, and 5 was 24.8, 19, 8.75, 16.7, 
and 12.4, respectively. Without the regenerator, or heat exchanger, 
the boiler horsepower per hour required for pasteurizing would have 
been increased to 35.6, 26.78, 22, 37.5, and 45.1, respectively. Thus 
the average increase in fuel would have been 96.8 per cent, or practi- 
cally doubled. In addition to the direct saving in fuel due to exchang- 
ing the heat from the hot milk coming from the holding tank to the 
cold raw milk on its way to the heater, there is an average saving 
in refrigeration of approximately 60 per cent, for it is evident that 
the heat taken out of the hot milk in the regenerator takes just 
so much work off the cooler. By referring to the temperature bal- 
ance in the table it will be noted that the drop in temperature in the 
