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

204 SEA WATER DISTILLATION. Surfaces—Condensing and Cooling. (1) Cooling Surface. 74. For producing cold drinking water, it will be re- membered, there were two sets or sheaves of surfaces, one above the other (see Fig. 18, p. 138), and that in double distilling apparatus the lower tube surface—that is, the set of tubes used for cooling the distilled water— varied according to the quantity of water to be cooled. Thus, if the secondary water only, just produced in the upper set of tubes, has to be cooled, the cooling surface has to be calculated for the quantity of such secondary water only, but if the primary water from evaporator coil drain is mixed with the secondary water, the sur- facing of the cooling tubes must be sufficient to deal with both waters. Such cooling surface will obviously have to be increased in the same proportion as the economy of the primary water is to that of the secondary water. So that, if x square feet of cooling surface is sufficient for the secondary water only, this x surface will have to be x + (x x 1'2) = 2’2x, total, if the economy is 1’2. If the economy is I-25, then the surface of the cooling tubes will have to be x + (x x T25) — 2-25æ, total. 75. This rule has to be given effect to in all types of multiple distillation, as the cooling surface must be equal to deal with the total production of all the water. The cooling surface is, therefore, increased at each successive distillation. (2) Condensing Surface. 76. The above rule, however, applies to the distiller cooling surface only, for it is observable that only the water increases at each successive distillation—i.e., with