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

THE EVAPORATOR. I 17 therefore, good for heating up the feed-water to a small extent, say up to 120° or 130°. 108. Method (2) of heating the feed-water—viz., by using the sensible heat still remaining in the primary water, after the latent heat of the primary steam has been abstracted from it for evaporation purposes—can be effected as follows :—This heat can be utilised by means of a heater of usual type—i.e., a nest of tubes inside a casing, the hot primary water going through the tubes, and imparting its heat to the feed-water going through the casing surrounding the tubes. 109. Fig. 14 shows the type of heater in question. The hot primary water enters the heater at (P), and passes through the tubes (T), escaping at the bottom outlet for return to the boiler. The feed-water enters at (F.I.) into the casing, surrounds the hot tubes which impart to it the heat of the primary water inside them, and finally the heated feed-water escapes at (F.O.) to run into (or be pumped into) the evaporator casing. Many other types of heaters can be designed, but Fig. 14 shows a simple design which has been found to work well. Note.—It should be noted that as much heat as possible should be abstracted from the primary water, as such water goes back to the hot well or elsewhere for return to the boiler. 110. The actual heat that is used, in the above way, to heat the feed-water may be arrived at as follows :— Suppose 1 ton of distilled water—i.e., gained water— has to be produced per hour, and that the primary steam pressure is to be 25 lbs. (whose sensible heat = 266° F., and whose latent heat = 927 B.T.U.). The feed-water