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

122 SEA WATER DISTILLATION. in mind, also that the heater coil has not to convert feed- water into steam, but simply to raise its temperature a few degrees. 118. In settling the amount of surface for the heater, it must be remembered that only primary water is to be used for heating purposes. No primary steam should be allowed to pass along with the primary water, as no benefit will thereby be derived. It is true the heater will be made more effective, but then this will only be done by robbing the evaporator of the primary steam thus used in the heater, and such primary steam would be very much better employed in evaporative work—i.e., by con- verting sea water into steam by its latent heat, than using some of this latent heat in heating up the feed-water. Feed Heater—Its Construction. 119. The heater is best constructed with a shell, com- posed either of steel or gun-metal. The position of the heater is best vertical, so that the two waters—viz., the feed-water on the one hand, and primary water on the other—are able to flow, or can be forced, evenly through the heater. The primary water inlet—i.e., from the coil drain—would appear to be best placed at the top of the heater, and the feed-water inlet at the lower end of the casing. This might be reversed by making the primary water enter at the bottom of the heater and the feed- water at the top, but the former would appear to be preferable. 120. The heating surfaces can be made of straight tubes or coils, and the material should be solid-drawn copper ; if the tubes are expanded into tube plates, gun-metal of Admiralty quality should be used for the plates. The tubes, and all parts through which the primary