EVAPORATION 



319 



difference here, and since the transmission coefficient is least in the last 

 cell, this end will follow when the cells are all of equal size. 



Computation of the Conditions in a Multiple Effect. Let the temperatures 

 in the four cells of a quadruple be 212 F., 203 F., 185 F., and 130 F. 

 Let i Ib. steam at 227 F. and 6 Ibs. juice at 212 F. enter the first effect, 

 the specific heat of the juice being 0-9. 



The i Ib. steam at 227 F. condensing and passing away as water at 

 212 F. to Cell 2 gives up 975-2 B.T.U. and evaporates 1-006 Ibs. of water 

 from and at 212 F. 



There passes on to the calandria of the second cell 1-006 Ibs. of steam 

 at 212 F. and i Ib. of water also at 212 F. ; 2-006 Ibs. water leave the 

 calandria of Cell 2, so that in all 978-8 B.T.U. have been surrendered, and 

 the corresponding evaporation from and at 203 F. will be 1-013 Ibs. water. 

 Simultaneously 4-994 Ibs. of juice pass from Cell i to Cell 2, and in cooling 

 down from 212 F. to 203 F. give up 4-994 X (212 203) X 0-9 B.T.U., 

 or 40-5 B.T.U., corresponding to the evaporation of 0-042 Ib. water.* The 

 total evaporation in Cell 2 is then i 055 Ib. of water. 



Following on these lines the total evaporation in Cell 3 is determined as 

 1-165 lb-' and tnat of Cel1 4 as I< 47 6 tt>. water. 



The final state of the apparatus is then as follows : 



Water at 130 F. discharged from Calandria 4 

 Steam at 130 F. discharged from Vapour space 4 

 Syrup at 130 F. discharged from Cell 4 



4 -226 Ibs. 

 i -476 Ibs. 

 i -298 Ibs. 



These results are shown diagrammatically in Fig. 184. 

 The total evaporation per Ib. of steam is 4-702 Ibs., and expressed per 

 unit of juice admitted the final position is : 



Juice at 212 F. 



Condensed water at 130 F. 



Syrup at 130 F. and o -6 specific heat 



Vapour at 130 F. 



Steam admitted at 227 F. 



Water evaporated 



i -ooo 

 0-704 

 o -216 

 o -246 

 0-167 



0-784 



This computation gives in a quadruple effect 4-702 Ibs. water per Ib. 



* This is known as " self-evaporation." 



