THE EVAPORATION OF THE JUICE TO SYRUP. 



Increase of the Capacity of a Multiple Effect. From 



what has been written it follows that the capacity of a multiple can be 

 increased along the following lines : 



1. By keeping the heating surfaces clean. Evaporators are sometimes 

 constructed with a spare vessel, so that one vessel is always out of use ; the 

 apparatus can then be cleaned without stopping operations. 



2. Increase of the fall of temperature, effected either by increasing the 

 pressure of the heating steam or by increasing the vacuum in the last body ; 

 where exhaust steam is used in the first body the increase in pressure is 

 limited by the demands of the motors, and according to Claassen's dictum 

 (supra) an increase in the vacuum in the last body over and above 60 cm. 

 or 23'7 inches is not attended with material benefit. 



3. Decrease of the height of the liquid contained in the calandria as 

 exemplified in the Welner-Jelinek design. 



4. By ' ruissellement,' best obtained in a vertical tube apparatus, by 

 maintaining a low level of juice in the apparatus. 



5. By increase in the rapidity of the circulation. 



Temperatures in the Multiple. It has already been shown 

 that the fall in temperature from vessel to vessel, and consequently the 

 temperature in each vessel depends on the heating surface in each vessel, and 

 on the coefficient of transmission of heat in each vessel ; the ratio of heating 

 surfaces to obtain an equal fall of temperature from vessel to vessel as calcu- 

 lated by Hausbrand have already been given ; if, then, as is generally the 

 case, the heating surfaces are equal, the fall of temperature from vessel to 

 vessel will be in inverse proportion to these ratios. 



In the triple the total fall will be divided between the three vessels in 

 the ratios : 



First Tessel 1 1.44'+ 3-445 = ' 1698 



+ l-44+ 3-445 

 Third vessel 1 + 1 . 4 7^ 3 . 445= -5857 



If the initial temperature of heating steam be 220 F., and the final 

 temperature be 130 F , the total fall is 90 F., of which there occurs in the 

 First vessel, 90 X '1698 = 15-3F., 

 Second vessel, 90 x '2445 = 22-0 F., 

 Third vessel, 90 X '5857 = 52-7 F., 

 and the temperature prevailing will be 



First vessel. Second vessel. Third vessel. 



204-7 F. 182-7 F. 130 F. 



315 



