320 



CHAPTER XVITI 



steam as the maximum possible evaporation. The method of computation 

 assumed that the condensed water in each cell passed on to the next with 

 complete transference of heat, and that the juice entered the first cell at 

 the temperature there prevailing. Under actual conditions the juice usually 

 enters at a lower temperature, the condensed water is not generally passed 

 on, and the exchange of heat is not complete. In addition, no account is 

 taken of radiation losses and of heat carried forward in the evacuation 

 of the incondensible gases. Further, as stated later, the exchange of heat 

 between condensed water and juice is very small, and some amount of super- 

 heating of vapours occurs. 



So great an economy can never obtain, and some experimental results 

 are given later, which may be compared with those computed above. 



With evacuation of the water separately from each cell the maximum 

 computed evaporation per pound of steam will be found to be from 4-3 to 

 4-4 Ibs. water. In a triple effect the evaporation as computed above will 

 be from 3-4 to 3-5 Ibs. with circulation of the condensed water, and from 

 3-1 to 3-2 Ibs. with its separate removal. 



In so far as the effect of introducing juice below the temperature of ebul- 

 lition in the first cell is concerned, it is to be remembered that heat consumed 

 in elevation of the temperature is not used in multiple effect. In a quadruple 

 effect the evaporation per pound of steam supplied will be as indicated below, 

 with juice introduced at the temperature shown and as computed on the 

 lines used above. 



According to the computations above there is a progressively increasing 

 evaporation in each cell, which with circulation of the condensed water is : 



Cell I. 



I -OOO 



21 -3% 



Cell II. 

 1-057 



Cell III. 

 i -164 

 24-8% 



Cell IV. 



i -479 

 3i '5% 



If the juice enter at B and leave at B w the total evaporation per 100 

 B, - B 



juice is 



If, in the case worked out in detail, the juice enter at 



13 Brix, it will leave at 60-8 Brix, and the total evaporation will be 



