Document a132rQy9bGMaKzRQobZ0R3qjY

American Society of Heating and Ventilating Engineers Guide, 1937 F is similar to D but is for dry air, devoid of all moisture or water vapor. For con venience, the approximate absolute temperature of 500 F is given at 40 F on the satura tion line for the purpose of calculating volume, weight per cubic foot, and relative density at partial saturation. METHOD OF USING THE CHART Example 8. Relative Humidity: At the intersection of the 78 F wet-bulb line and the 95 F dry-bulb line, the relative humidity is read directly on the straight diagonal lines as 46 per cent. Example 9. Dew Point: At the intersection of the 78 F wet-bulb line, the dew-point temperature is read directly on the horizontal temperature lines as 70.9 F. Example 10. Vapor Pressure: At the intersection of the 78 F wet-bulb line and the 95 F dry-bulb line, pass in a horizontal direction to the left of the chart and on the logarithmic scale read the vapor pressure as 19.4 millimeters of mercury. (Divide by 25.4 for inches.) Example 11. Total Heat Above 0 F in Mixture per Pound of Dry Air Saturated with Moisture: From where the wet-bulb line joins the saturation line, pass in a vertical direction on the 78 F dry-bulb line to its intersection with curve A and on the logarithmic scale at the left of the chart read 40.6 Btu per pound of mixture. The use of this curve to obtain, the total heat in the mixture at any wet-bulb temperature is a great con venience, as the number of Btu required to heat the mixture and humidify it, as well as the refrigeration required to cool and dehumidify the mixture, can be obtained by taking the difference in total heat before and after treatment of the mixture. Example 18. Grains of Moisture per Pound of Dry Air Saturated with Moisture: From 70.9 F dew-point temperature on the saturation line, pass vertically to the inter section with curve B and on the logarithmic scale at the left read 114 grains of moisture per pound. Example 13. Grains of Moisture per Cubic Foot of Mixture, Partially Saturated: From 70.9 F dew-point temperature on the saturation line proceed in a vertical direction to curve C, and on the logarithmic scale to the left read 83.3 which, divided by 10, gives1 8.33 grains. A temperature of 70.9 F is equal to an absolute temperature of 530.9, and 95 F equals 555, absolute temperature. Therefore, 5 30' 9 X 8.33 = 7.97 grains per 555 cubic foot of partially saturated mixture. Example 14. Grains of Moisture per Cubic Foot of Saturated Air: Starting,at the saturation line at the desired temperature, pass in a vertical direction to curve C and on the logarithmic scale at the left, read a number which, divided by*10, will give the answer. o ' Example 15. Weight per Cubic Foot of Dry A ir and Relative Density: From the point where, for example, the 70 F vertical dry-bulb line intersects curve E, pass to right side and read 0.075 lb; if cubic feet per pound are desired, divide 1 by this amount. The relative density is read immediately to the right as 1.00. Example .16. Weight of Dry Air per Cubic Foot of Saturated Mixture and Relative Density: From the point where, for example, the 70 F vertical line intersects the curve D, pass to the right and read weight per cubic foot as 0.07316 with a relative density of 0.9755 for saturated air at 70 F. ' Example 17. Weight of Dry Air per Cubic Foot and Relative Density of Partially- Saturated Air: Air at 50 F and a svet-bulb temperature of 46 F is to be heated to 130 F. The wet- and dry-bulb lines intersect at a dew-point temperature of 42 F. Pass to the left where this dew-point line intersects the saturation line and then pass in a vertical * direction to where the 42 F dry-bulb line intersects with curve D. Then pass directly to the right and read the weight per cubic foot of saturated air at 42 F as 0.07844 and the, relative density as 1.046. The absolute temperature at 42 F is 502, and at 130 F is 590. 502 Therefore, = 0.851. The weight of 1 cu ft of air at 50 F dry-bulb and 46 F wet-bulb when heated to 130 F is 0.07844 X 0.851 = 0.06675. and the relative density is 1.046X 0.851 = 0.89. 26 f- -. H 3 i Chapter 1--Air, Water and Steam PROPERTIES OF WATER Composition of Water. Water is a chemical compound (HjO) formed by the union of two volumes of hydrogen and one volume of oxygen, or two parts by weight of hydrogen and 16 parts by weight of oxygen. Density of Water. Water has its greatest density at 39.2 F, and it expands when heated or cooled from this temperature. At 62 F a U. S. gallon of 231 cu in. of water weighs approximately 8% lb, and a cubic foot of water is equal to 7.48 gal. The specific volume of water depends on the temperature and it is always the reciprocal of its density. (See Table 7.) Table 7. Thermal Properties of Water Tsicperature Deo F 32 40 50 60 70 80 90 100 no 120 130 140 ISO 160 170 180 190 200 210 212 220 240 260 280 300 350 400 450 500 550 600 700 Sat. Press. Lb per Sq In. 0.0887 0.1217 0.1780 0.2561 0.3628 0.5067 0.6980 0.9487 1.274 1.692 2.221 2.887 3.716 4.739 5.990 7.510 9.336 11.525 14.123 14.696 17.188 24.97 35.43 49.20 67.01 134.62 247.25 422.61 681.09 1045.4 1544.6 3096.4 Youths Cu Ft per Lb 0.01602 0.01602 0.01602 0.01603 0.01605 0.01607 0.01610 0.01613 0.01616 0.01620 0.01625 0.01629 0.01634 0.01639 0.01645 0.01650 0.01656 0.01663 0.01669 0.01670 0.01676 0.01690 0.01706 0.01723 0.01742 0.01797 0.01865 0.01950 0.02050 0.02190 0.02410 0.03940 Weight Lb per Cu Ft 62.42 62.42 62.42 62.38 62.31 62.23 62.11 62.00 61.88 61.73 61.54 61.39 61.20 61.01 60.79 60.61 60.39 60.13 59.92 59.88 59.66 59.17 58.62 58.04 57.41 55.65 53.62 51.30 48.80 .45.70 41.50 25.40 Specific Heat 1.0093 1.0048 1.0015 0.9995 0.9982 0.9975 0.9971 0.9970 0.9971 0.9974 0.9978 0.9984 0.9990 0.9998 1.0007 1.0017 1.0028 1.0039 1.0052 1.0055 1.0068 1.0104 1.0148 1.0200 1.0260 1.0440 1.0670 1.0950 1.1300 1.2000 1.3620 -- Water Pressures. Pressures are often stated in feet or inches of water column. At 62 F, with ft equal to the head in feet, the pressure of a column of water is 62.383ft lb per square foot, or 0.433ft lb per square inch. A column of water 2.309 ft (27.71 in.) high exerts a pressure of one pound per square inch at 62 F. Boiling Point of Water. The boiling point of water varies with the pressure; it is lower at higher altitudes. A change in pressure will always be accompanied by a change in the boiling point, and there will be a cor- 27