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

THE EVAPORATOR. 99 steam inside the coils, so that if used for heating the feed- water it has this amount of sensible heat to impart. This will be reverted to when dealing with the feed- water heater. (D) The Evaporator Shell or Casing. 69. Having treated of the surfaces of the evaporator, the casing or shell, as it is sometimes called, may now be ■dealt with. In shape it varies according to the form of coil that is fitted inside it. The evaporator casing is usually cylindrical and vertical, and the coils are fitted inside to the lower part, the upper part being devoted to the steam-room or space. (a) Steam-Room. 70. The steam-room should be of sufficient diameter •and height to allow the steam or vapour generated from the sea water in the lower part of the casing to escape ■easily, without risk of priming—that is, without carrying over any particles of sea water with it. This point re- quires some consideration, as the sea water is in a some- what violent state of ebullition, and if the space over the boiling brine is too contracted, the brine will rise and froth up, and eventually be carried over with the steam, so that the distilled water, when tested, will be found to ■contain more or less salt. 71. The question of what is a sufficient steam space to -allow is to a very great extent determined by experience, much depending upon the form of the casing, the position -of the coil, and the pressure under which the sea water is being evaporated, and quantity evaporated. 72. In theory, if water is being evaporated under high pressure, the steam delivered should be in smaller bubbles