10 



BULLETIN 85, U. S. DEPARTMENT OP AGRICULTURE. 



obvious that the 380,800 B. t. u. represented so much additional 

 heat over the exhaust-steam systems in tests Nos. 1, 2, and 3. 



As stated above, in test No. 4 the pasteurizing was done by live 

 steam from the boiler instead of exhaust steam, and by referring 

 to the tabulated results of tests it will be noted that the over-all 

 thermal efficiency of test No. 4 is only 43.7 per cent while that of 

 tests Nos. 1, 2, and 3 is 69.1, 60.6, and 69.7 per cent, respectively* 

 although the thermal efficiency of the heater in test No. 4 was the 

 greatest. 



The over-all efficiency is here taken as the ratio of the heat supplied 

 by the boiler to the steam to that absorbed by the cream. 



The thermal efficiency of the heater is the ratio of the available 

 heat in the steam supplied to the heater to that absorbed by the 

 cream. 



HEAT BALANCE. 



No heat balance is given in Table 2 because the pasteurizing 

 equipments in tests Nos. 1, 2, and 3 were installed in market cream 

 plants, that is, plants whose business consisted in the handling 

 and marketing of cream. The cream as received from auxiliary 

 creameries was first run through separators, the result being a 

 heavy cream containing about 40 per cent fat. This heavy cream 

 on the way to the coolers was mixed with skimmed milk in the correct 

 proportion to produce a cream containing a predetermined amount 

 of fat. In view of the methods employed in these plants, it was 

 impractical to get out a heat balance showing the distribution of 

 heat in the pasteurizing cycle. 



Table 2. — Results of tests of four cream-pasteurizing plants. 

 HEATING. 





Plant No. 





1 



2 



3 



4 



Time of operation hours. . 



3.53 



1.733 



1.5 



1.166 



Amount of cream pasteurized pounds. . 



50, 683 



6,928 



5,019.5 



4,571 





5,589.5 



1,088 



647.5 



629 



Heat supplied by boiler to steam, 80 pounds pressure, 











B. t.u.. 



6, 437, 646 



1,253,478 



746,003 



617,113 



Heat in steam required to drive pasteurizing equipment, 











B.t. u.. 









380,800 





5,589,500 



1,088,000 



647,500 



529,000 



Total boiler horsepower developed for pasteurizing, 











B.H. P.. 



193.2 



37.6 



22.4 



80.9 



Boiler horsepower per hour developed for pasteurizing, 











B.H. P.. 



54.7 



21.7 



14.9 



25.6 



Total heater horsepower consumed for pasteurizing. do 



167.7 



32.6 



19.4 



15.9 



Heater horsepower per hour consumed for pasteurizing, 











B.H. P.. 



47.5 



18.8 



13.0 



13.6 





262 



184 



224 



153 



Cream pasteurized per heater horsepower do 



302 



212 



258 



287 



Coal burned in pasteurizing do 



1,030 



200 



119 



160 



Cream pasteurized per pound of coal do 



Total U. t. u. absorbed dv cream B. t. u.. 



The over-all thermal efficiency of pasteurizing equip- 



49.2 



34.6 



42.2 



29.0 



4, 447, 433 



760,030 



520, 171 



436,176 











ment per cent.. 



69.1 



60.6 



69.7 



43.7 



Thermal efficiency of heater do 



79.4 



69.8 



80.3 



82.5 



