Document M4E2M8MKMM53nVdRGgaXy01pV

Heating Ventilating Air Conditioning Guide 1939 A is the total heat in Btu contained in the mixture above 0 F, and is to be referred to the column of figures at the left side of the chart. Enthalpy of the liquid is not included. B is the grains of moisture or water vapor accompanying each pound of dry air and is to be referred to the figures at the left side of the chart. C is the grains of moisture or water vapor per cubic foot of saturated mixture, and is to be referred to the figures at the left side of the chart which are to be divided by 10. D is the weight in decimal fractions of a pound of dry air in one cubic foot of the saturated mixture, and is referred to the first column of figures to the right of the satura tion line between the vertical dry-bulb temperature lines 170 and 180 F. The relative density of the mixture is read in a similar manner from the same curve by the column of figures between the vertical dry-bulb temperature lines 180 and 190 F. E is similar to D but is for one cubic foot of the saturated mixture. 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. A. 8, C, D. E, F=Directrix lines 0. B. LDr/ bulb line 0. P. L=Dew point line______ R. H. L=Relative humidity fine W.B. L-Wet bulb line Si?Saturation line G. P. Lb*Grains moisture sat mixture per lb dry air R. D. 0. S.=Relative density dry air per cu ft saturated T. H.*ToUI heat sat mixture per lb dry air W.p.tF. S.=Weight per cu ft in lbs saturated V. P.sVapor pressure in mm mercury R, O. S=Relative density per cu ft saturated- G. P. C. F. S.=Grains moisture per cu ft sat air W. P.C. F. D.Weight per cu ft in ibs dry W. D. A. C. F. S.=WeigW dry air per cu ft in lbs saturated R. 0. D.=Relative density per cu ft dry G.P.C.F.* ** % = G. P. C. F. at partial saturation Abs temp at D. B. wpaF-* Ate temii at w- p-c-F- ** P""*1 Mtorafon on* Abs temp at 0. P. a R. D. at partial saturation * Abs temp at 0. a Fig. 2. Diagrams Showing Procedure to Follow in Using Bulkeley Chart 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 26 Chapter 1. Air, Water and Steam 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 IS. 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 IS. 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, gives 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, 530 9 X 8.33 = 7.97 grains per cubic foot of partially saturated mixture. Example H. 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. Example 15. Weight per Cubic Foot of Dry Air 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 wet-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 den5s0i2ty as 1.046. The absolute temperature at 42 F is 502, and at 130 F is 590. 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 1.046 X 0.851 = 0.89. PROPERTIES OF WATER Composition of Water. Water is a chemical compound (HsO) 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 8lb, 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). 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.