THE EVAPORATION OF THE JUICE TO SYRUP. 



Jelinek estimated that the pump should displace -3 cubic metre per kilo, of 

 vapour ; this equals 4 -8 cubic feet per Ib. of vapour, and as it applies to European 

 conditions with cold cooling water would be on the low side for tropical conditions. 



Horsin Deon estimates that the wet air pump should displace twelve 

 times the volume of water to be discharged. These rules will be found to 

 give capacities larger than are often observed in practice. 



With dry vacuum it has been found that a much smaller cylinder capacity 

 than that required for a wet air pump is necessary, and as an empirical rule it 

 may be stated that the displacement of the dry air pump need be only one- 

 third that necessary for a wet air pump. 



Cooling Towers. In districts where water is scarce it is necessary 

 to use over and over again the condenser water, which has thus to be cooled 

 each time after use ; cooling is effected by the action of the air applied either 

 in open or closed towers. The open type generally consists of a skeleton 

 framing of angle iron up to 30 feet high with three or four lower stages ; on 

 these are placed layers of faggots or brushwood ; the water is delivered by a 

 pump to the highest stage and distributed by gutters over the faggots and 

 falling down is collected in a reservoir at the bottom. A second design consists 

 of a series of steps down which the water flows in a cascade. 



Alternatively, a brick shaft with a water distributing device inside is 

 employed ; in this case a fan is required to force cooling air up the shaft. The 

 United States makers of the Worthington pump employ such a scheme. The 

 distributing device is a sprinkler (of principle identical with that described on 

 page 305) ; the cooling surface consists of a number of cylindrical tiles placed 

 vertically the water flowing down these both internally and externally. 



In a fourth method, injectors of the Korting pattern arranged round the 

 periphery of a pipe throw the warm water upwards in a fine shower. 



Under tropical conditions with cooling air at about 80 F., and condenser 

 water at about 140 F., at the very least 1 sq. ft. cooling surface will be 

 required per gallon of water per hour, to be cooled to 100 F. and an excess of 

 this quantity is to be desired. 



Scale in Evaporators. Scale deposited on the tubes of evaporators 

 is due either to suspended matters carried forward in the juice or to the 

 deposit of dissolved bodies due to the concentration of the juice. 



The elimination of the first cause can be obtained by a filtration of the juice 

 en masse, either through mechanical filters or through sand filters ; a useful 

 effect may also be obtained by passing the juice through strainers of very fine 

 mesh. A good filtration of the juice has an enormous effect in the prevention 

 of scale, and accordingly in increasing the efficiency of the apparatus. The 

 interfiltration of the partially concentrated juice on its way from vessel to 

 vessel with the view of removing the matter deposited on concentration has 

 also been employed. 



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