the wide use of the double-effect plant in the Naval Service and its added efficiency. A double-effect plant was therefore arranged for test. Each shell contained about 24 square feet of evaporating surface in the form of coils connected between manifolds as shown in the photographs, figures 7 and 9. A steam pressure of 250 pounds was available in the main line. The second-effect vapor discharged to a distiller condenser through a vapor feed heater, and atmospheric pressure was carried on the second effect shell. The vapor feed heater heated the feed for both effects to about 195 degrees, and the feed for the first effect was further heated by a coil drain heater. The capacity at which it was desired to operate was 120 gallons of water per day per square foot of total surface, which is double the present rating for Navy evaporators. From the expected efficiency of the double-effect plant this would require about 1,200 pounds of steam per hour to be supplied to the first effect coils. From Napier's formula, for 250 pounds steam pressure in the line, the W = PA orifice required was computed to be 0.335 inch diameter. A brass plate 1/8 inch thick, with a hole in the center 0.335 inch in diameter, was placed between two flanges in the steam line to the coils of the first-effect evaporator. The full line pressure of 250 pounds was carried on the line leading to the orifice. Atmospheric pressure was carried on the second-effect shell. The water in each shell was carried at such a height as to submerge the coils. This level was determined by trial, as will be explained later. A water seal was kept on the coil drain by means of traps part of the time, and drain pots part of the time. This insured that all the steam entering the coils was condensed therein and only condensate allowed to discharge from the coils. The log plot of the results of the first run is given in the insert, figure 5. On this are plotted the coil pressures, temperature differences, capacities, heat transfer coefficients and salinities for each of the two effects. The salinity on the first effect was allowed to increase to 3/32nds and was maintained at that value throughout the test. The salinity of the second effect was varied, in order to observe the effect of a variable salinity on the action of the evaporator. The second-effect salinity was allowed to increase to 5/32nds, was then slowly decreased to that of Severn River water, which is less than 1/32nd, was increased to 5/32nds again, reduced to below 1/32nd, and increased to 3/32nds. Throughout the series of 26 hours the steam flow to the plant was constant except for a slight falling off when the line pressure fell below 250 pounds at the 6th hour. The pressure in the second-effect coil started at 20 pounds gage and increased to 52 pounds gage at the 6th hour, when the salinity was 5/32nds. Upon the reduction of the salinity the pressure fell and followed the salinity till at the end of the 26th hour the pressure was 55 pounds when the salinity was 3/32nds. The first-effect coil pressure started at 36 pounds gage and rose and fell, of necessity following the second-effect coil pressure (which was the firsteffect shell pressure). A first-effect coil pressure of 100 pounds was reached at the 7th hour. It then decreased slowly to 47 pounds, increased to 150 pounds, decreased to 82 pounds, and reached 150 pounds at the 26th hour, with a salinity of 3/32nds on both effects. The temperature difference for the second effect varied, following the second-effect salinity, but the temperature difference for the first effect increased uniformly throughout the series from 24 degrees at the start to 65 degrees at the finish. Throughout all this period the capacity of both effects was practically constant, such variations as took place being due to variations in heat losses of the blow-down and the coil drain. (It should be noted that the run was not made non-stop. The plant was shut down each night and the salt water allowed to remain in the shell. In the morning the operation was resumed, and in each case the conditions obtained on starting in the morning corresponded |