is subtracted from 9.403 cu. ft., since the volume is less for a pressure of 44.7 lb. than for a pressure of 44 lb. 9.268 X 14 129.752 cu. ft. EXAMPLE 5.-Find the weight of 40 cu. ft. of steam at a temperature of 254° F. SOLUTION.-The weight of 1 cu. ft. of steam at 254.0020, from the table, is .078839 lb. Neglecting the .0020, the weight of 40 cu. ft. is, therefore, .078839 X 40 = 3.15356 lb. EXAMPLE 6.-How many pounds of steam at 64 lb. pressure, absolute, are required to raise the temperature of 300 lb. of water from 40° to 130° F., the water and steam being mixed? = = SOLUTION.-The number of heat units required to raise 1 lb. from 40° to 130° is 130-40 90 B. T. U. (Actually a little more than 90 would be required, but the above is near enough for all practical purposes.) Then, to raise 300 lb. from 40° to 130° requires 90 X 300 27,000 B. T. U. This quantity of heat must necessarily come from the steam. Now, 1 lb. of steam at 64 lb. pressure gives up, in condensing, its latent heat of vaporization, or 905.9 B. T. U. But, in addition to its latent heat, each pound of steam on condensing must give up an additional amount of heat in falling to 130°. Since the original temperature of the steam was 296.805° F. (see table), each pound gives up by its fall of temperature 296.805130 166.805 B. T. U. Therefore, each pound of the steam gives up a total of 905.9166.805 1,072.705 B. T. U. It will, therefore, take 27,000 1,072.705 25.17 lb. of steam to accomplish the desired result. With the steam tables a reliable thermometer may be used for ascertaining the pressure of saturated steam or for testing the accuracy of a steam gauge. The temperature of the steam being measured by the thermometer, the corresponding absolute pressure is found from the steam tables; the gauge pressure is then found by subtracting 14.7 from the absolute pressure. Thus, the temperature of the steam in a condenser being 1420, we find from the steam tables that the correspond. ing absolute pressure is 3 lb. per sq. in., nearly. 12345 6 FRE 7,325 102.018 70.010 1,043.015 1,113.055 .003027 330.4 20,623 170.173 138.401 7 176.945 145.213 8 182.952 151.255 9 188.357 156.699 10 193.284 161.660 11 197.814 166.225 12 202.012 170.457 13 205.929 174.402 14 209.604 178.112 14.69 212.000 180.531 5,588 4,530 8 20 227.964 196.655 954.814 1,151.469 .050696 19.730 22 233.069 201.817 951.209 1,153.026.055446 18.040 24 237.803 206.610 947.861 1,154.471 .060171 16.620 26 242.225 211.089 944.730 1,155.819 .064870 15.420 28 246.376 215.293 941.791 1,157.084.069545 14.380 30 250.293 219.261 939.019 1,158.280 .074201 13.480 1,231.0 1,126.0 1,038.0 962.3 897.6 841.3 791.8 948.0 .088067 11.360 708.8 .092657 10.790 673.7 40 267.168 236.386 927.040 1,163.426 .097231 10.280 642.0 .101794 .106345 48 278.348 247.752 919.084 1,166.836 .115411 8.665 540.9 50 280.904 250.355 917.260 1,167.615 60 292.575 262.248 908.928 1,171.176 .142362 62 294.717 264.433 907.396 1,171.829 72 304.669 274.597 900.269 80 311.866 281.952 895.108 1,177.060 5.917 369.4 90 320.094 290.373 889.196 1,179.569 .208525 4.796 299.4 1,180.045 .212892 4.697 293.2 1,180.511 .217253 4.603 287.3 1,180.970 .221604 4.513 281.7 1,181.422 .225950 4.426 276.3 .230293 4.342 271.1 .241139 4.147 258.9 .251917 3.969 247.8 VENTILATION. GENERAL INFORMATION. Ventilation is a process of moving foul air from any space and replacing it with fresh air. A positive displacement, however, does not take place; the incoming fresh air chiefly dilutes the foul air to a point suitable for healthful respiration. Pure air, such as exists in the open country, contains about 4 parts of carbon dioxide, CO2, per 10,000 parts of air, while badly ventilated rooms often contain as much as 80 parts of CO2 per 10,000 of air. Hygienists, after careful study, have decided that an increase of 2 parts of CO2 per 10,000 of air should be accepted as the standard of respirable purity, and any excess of CO2 above this may be considered as vitiation. PRODUCTION OF CO2 PER HOUR. Taking the figures above given-4 parts of CO2 per 10,000 parts of fresh air, and 6 parts (4+2) per 10,000 of vitiated air-as the standard for proper health conditions, it is found that 3,000 cu. ft. of fresh air per hour is necessary for each adult person. If a different standard than 6 is used, the number of cubic feet per person will be found by dividing 6,000 by the difference between this standard and 4. If any lights deliver their products of combustion into the room, the amount of CO2 given off by them should be converted into its equivalent in men, thus: One ordinary gas light equals, in vitiating effect, about 5 men, an ordinary lamp 13 men, and an ordinary candle about man. It is considered good practice to allow 2,000 cu. ft. of fresh air per hour for each inmate of a room or auditorium. |