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

THE EVAPORATOR. 83 secondary steam of one evaporator becomes the primary steam of the next, and the secondary steam of the second evaporator becomes the tertiary steam of the third evaporator, and so on, as long as the successive distil- lations are carried. As, however, each successive distilla- tion is less in degree than the preceding one, a limit is soon reached. The matter will, however, be more fully dealt with in the chapter on “ Multiple Distillation/’ Form of Heating Surfaces. 38. Io proceed with the usual type of evaporator—that is, one that is heated by steam inside a coil—we will now deal with the form and shape of such coils or tubes. 39. Evaporator makers differ very considerably in the form of surface they prefer, and there have been consider- able changes made in the construction of these surfaces from the earliest type of evaporators made. 40. Until about fifteen or twenty years ago, the only form of evaporating surface used was a sheaf or nest of tubes placed vertically, see Fig. 5, the primary steam entering at A, and after doing its work inside the tubes, the primary water thus formed fell into a bottom pan,’ and was blown away at B. These vertical tubes T were expanded in gun-metal tube plates at top and bottom, and a cap, C, to which the steam inlet at A was connected, was fitted at the upper end. The primary steam dis- tributed itself inside the tubes, where it was condensed into primary water, by transferring its latent heat to sea water outside these tubes. 41. In these early days there was very little provision made for cleaning these surfaces. A very small mud door, D, was fitted to the lower end of the casing, through