WATER. Water at Different Temperatures. Freezing point at sea level.......................................................................................... Point of maximum density.. British standard for specific gravity.. Boiling point at sea level.... Weight per cu. ft. at 32 deg. Fahr. 46 39.1 46 TABLE NO. IV. BOILING POINT OF WATER AT DIFFERENT PRESSURES. ALSO AT DIFFERENT TEMPERATURES. 88° in 1 pound of the steam. It is, therefore, the latent heat of the water which remains unevaporated in 1 pound of the steam. Dividing this result by the latent heat of steam at the boiler pressure, that is, by the heat required to completely evaporate 1 pound of steam at the boiler pressure, gives the weight of suspended water in 1 pound of the boiler steam. Multiplying this result by 100 gives the number of pounds of suspended water in 100 pounds of the boiler steam. This is the per cent of moisture. To finish the calculation: Latent heat of suspended water in 1 pound of boiler 1,176.5 29.7 B. t. u. steam 1,206.2 Latent heat of 1 pound of saturated steam at boiler pressure, 900.9. Weight of suspended water in 1 pound of boiler steam 29.7900.9 0.032 pound. Weight of suspended water in 1 pound of boiler steam 0.032 X 100 = 3.2 pounds. Per cent of moisture in steam, 3.2. Example: If water apparently evaporated is 11,000 pounds, and the calorimeter test shows that the steam contains 3 per cent of moisture, how many pounds of water have been actually evaporated? Answer, 10,670 pounds. Finding Weight of Water Evaporated Per Pound of Combustible. This is a simple matter after finding the weight of water actually evaporated and the number of pounds of combustible consumed in the test. Divide the weight of water evaporated by the weight of combustible. Example: Pounds of water actually evaporated, 81,145. Pounds of combustible, 8,280. How many pounds of water were evaporated per pound of combustible? Answer, 9.8 pounds. Finding Equivalent Weight of Water Evaporated into Steam from and at 212° F. It would be impossible to compare different boiler tests without reducing them to standard conditions. The standard conditions of evaporation are water at 212° F. evaporated into steam at 212° F. To evaporate 1 pound of water at 212° F. into steam at 212° F. requires 965.7 British thermal units of heat. Hence a pound of steam at 212° contains 965.7 B. t. u. more of heat than is contained in a pound of water at 212°. A pound of water at 212° contains 212 B. t. u., reckoned from 0°. Therefore, the total heat of a pound of steam at 212°, reckoned from zero, is 965.7+ 212, or 1,177.7 B. t. u. In the evaporation test the temperature is higher than 212°, and the pressure higher than atmospheric pressure. We must find how much water at 212° would have been evaporated into steam at 212° by the amount of heat that was actually used. This can be found as follows: Multiply the total weight of water evaporated under the actual conditions by the total heat of steam under the actual conditions minus heat of feed-water, and divide by 965.7. The same rule can be put in the following form, which may make it more clear. The water that would have been evaporated from and at 212° has the same ratio to the water actually evaporated that the heat of steam under the actual conditions has to the heat of steam at 212°. To simplify this calculation, a table of factors of evaporation (Table VI) is given. Find from the table the factor of evaporation for the boiler pressure and temperature of feed-water as used in the test. Multiply the weight of water evaporated under the actual conditions by this factor. The result will be the equivalent weight of water at 212° into steam at 212°. The usual method is to find first the weight of water evaporated per pound of combustible under the actual conditions and multiply this number by the factor of evaporation. The result is the weight of water at 212° into steam at 212° per pound of combustible. Examples: 1. If 11 pounds of water per pound of combustible are evaporated under actual conditions, and the factor of evaporation is 1.06, what is the equivalent weight of water at 212° into steam at 212° per pound of combustible? Answer, 11.66 pounds. 2. If 11.5 pounds of water per pound of combustible are evaporated under the actual conditions, and the temperature of feed-water is 200° F. and boiler pressure is 75 pounds, what is the weight of water at 212° into steam at 212° per pound of combustible?Answer, 12.03 pounds. Finding Cost of Evaporating 1,000 Pounds of Water. Having found the weight of water evaporated into steam from and at 212° per pound of combustible, we can find the cost of evaporating 1,000 pounds of water, standard conditions, as follows: (1) Find weight of combustible required to evaporate 1,000 pounds of water; (2) find weight of coal required to furnish this weight of combustible; (3) find cost of this weight of coal. |