A Practical Manual On Sea Water Distillation
With A Description Of The Necessary Machinery For The Process

THE EVAPORATOR. II9 To meet the above requirement, the heat available is— 927 units, for every lb. of primary steam converted into water—latent heat. 116 units, for cooling down the primary water from 266 to 150—sensible heat. 1,0 43 units, available. Therefore, as 1,043 : 1,104 :: 1 : T06 (nearly)—i.e., l‘O6 lbs. of primary steam will be converted into primary water for the production of every lb. of gained water, and the primary water will leave the heater at 150°. 111. But if the feed-water had not been heated by using the 116 units out of the primary water heat, the economy would have been as follows :—As 927 : 1,104 :: 1 : T19— i.e., 119 lbs. of primary water for every lb. weight of gained steam produced. 112. The economy of 1’06 is, of course, ideal, as no allowance is made for waste of heat by radiation, which is considerable, especially if the evaporators (during trials) are not lagged on the outside of the casing, a recent condition sometimes imposed (but the reason of it is difficult to account for). 113. The economy, in actual practice, will, therefore, be more than 1'06, and the specified limit imposed by the Admiralty of 1’2 will be much nearer actual results than the ideal of 1'06. Heaters, Lagging of—Position. 114. The heater should be lagged on the outside, and such lagging may consist of the same material used for the evaporator shell, and the heater should be placed close to the evaporator, where it is fed, so that the feed-water