CANE SUGAR. 



Vapour Pipes. Taking the temperature of the vapour from the first 

 vessels as 206 F., 1 Ib. occupies 29-6 cubic feet; at a velocity of 100 feet per 

 second, the area of the pipe must be '657 square feet, corresponding to a 

 diameter of 1 1 inches. The temperature of the vapour from the second vessel 

 being taken as 177 F. will occupy 53*4 cubic feet per Ib., and under the same 

 velocity demands a vapour pipe 1 5 inches in diameter. Finally, for the pipe 

 leading to the condenser, allowing here a velocity of 150 feet per second, a 

 diameter of 21 inches is obtained; 1 Ib. of vapour at 132 F. occupying 

 152 '4 cubic feet. 



Injection Water. Assuming the vacuum in the condenser is 

 27*5 inches, the corresponding temperature is 104 F., and the temperature of 

 vapour given off in the last body may be taken as 134 F. At this temperature 

 the latent heat of steam is 1022 B.T.U., so that in condensing 1 Ib. of vapour 

 at 134 F. and cooling to 104 F. (corresponding to a vacuum of 27'5 inches) 

 1052 B.T.TJ. are absorbed. Allowing the injection water to be of tempera- 

 ture 84 F., each pound of water absorbs 20 B.T.TJ., so that 52-6 Ibs. water 

 per pound of vapour will be required, and to obtain this result at least 

 10 per cent, or 20 per cent, more water must be admitted. 



It is, however, only in exceptional cases that so large an amount of 

 injection water is admitted, and the temperature of the discharge is more 

 frequently 115F. to 120F. If the temperature of injection water be again 

 taken as 84 F., to obtain discharge water at this temperature, the quantity of 

 injection water required is only thirty times as much as the vapour to be 

 condensed, and this is the quantity usually allowed for in design. The 

 objection to admitting the larger quantities is the accompanying increase in 

 size of the pump, but the economy is only effected at the expense of the 

 vacuum in the last body, and consequently of the efficiency of the heating 

 surface as a whole. , 



The size of the injection pipe to deliver a definite quantity of water 

 depends on the head, the length, and diameter of the pipe, and the number of 

 bends. The theory of the flow of water in pipes is too complex to be 

 reproduced here, but a table is given below showing the velocity of water at 

 exit from pipes of diameter 4 inches to 12 inches, for lengths of from 40 feet 

 to 100 feet, and with one, two, or three right angle bends. The table has 

 been calculated from the latest formulae ; a constant head of 1 6 feet has 

 been assumed corresponding to a 25 inch vacuum, and a height of 12 feet of 

 entry of injection water above level in well. 



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