Document ZOeve3epEw1M2q0yR2o0XmmV

24 Chapter 1 1945 Guide Table 9. Weight-of~Saturated-and-Partly-SaturatedAir* Dbt-Bolb Temp . Deo F 28.5 Weight op Saturated Air tor Various Barometric and Htgrometric Conditions--Pounds per Cubic Foot - Barometric Pressure Inches of Mercury 29.0 29.5 30.0 30.5 31.0 % Increase In Weight Per 0.1 In. Rise in Barometer Approx. Average Increase in Weight Per Dbg Wet-Bulb Depression 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 - ,.74 76 .78 80 82 84 86 88 90 92 ' 94 96 .. 98 100 0.07703 0.07839 0.07671 0.07806 0.07638 0.07772 0.07605 0.07739 0.07974 0.07940 0.07907 0.07873 0.07573 0.07706 0.07541 0.07674 0.07509 0.07641 0.07477 0.07609 0.0744S 0.07576 0.07413 0.07544 0.07381 0.07512 0.07350 0.07479 0.07840 0.07806 0.07773 0.07740 0.07707 0.07674 0.07642 0.07609 0.07318 0.07447 0.07287 0.07415 0.07255 0.07383 0.07224 0.07352 0.07576 0.07544 0.07512 0.07479 0.07193 0.07320 0.07161 0.07288 0.07130 0.07256 0.07098 0.07224 0.07447 0.07414 0.07382 0.07350 0.07067 0^07192 0.07035 0.07160 0.07004 0.07128 0.06972 0.07096 0.07317 0.07285 0.07252 0.07220 0.06940 0.07064 0.06909 0.07032 0.06877 0.07000 0.06845 0.06967 0.07187 0.07155 0.07122 0.07089 0.06812 0.06934 0.06780 0.06901 0.06748 0.06868 0.06715 0.06835 0.07056 0.07022 0.06989 0.06955 0.06682 0.06801 0.06648 0.06768 0.06615 0.06734 0.06581 0.06700 0.06921 0.06887 0.06853 0.06818 0.08110 0.08075 0.08041 0.08007 0.07973 0.07939 0.07905 0.07872 0.07838 0.07805 0.07772 0.07739 0.07706 0.07673 0.07640 0.07607 0.07574 0.07541 0.07508 0.07475 0.07442 0.07410 0.07377 0.07343 0.07310 0.07277 0.07244 0.07211 0.07177 0.07143 0.07109 0.07075 0.07041 0.07006 0.06972 0.06937 0.08245 0.08210 0.08175 .0.08141 0.08106 0.08072 0.08038 0.08004 0.07970 0.07936 0.07902 0.07868 0.07835 0.07801 0.07768 0.07734 0.07701 0.07668 0.07634 0.07601 0.07568 0.07534 0.07501 0.07467 0.07434 0.07400 0.07366 0.07333 0.07299 0.07264 0.07230 0.07195 0.07161 0.07126 0.07091 0.07055 0.08381 0.08345 0.08310 0.08274 0.08239 0.08205 0.08170 0.08135 0.08101 0.08066 0.08032 0.07998 0.07964 0.07930 0.07896 0.07862 0.07828 0.07794 0.07760 0.07727 0.07693 0.07659 0.07625 0.07591 0.07557 0.07523 0.07489 0.07454 0.07420 0.07385 0.07351 0.07316 0.07280 0:07245 0.07209 0.07174 0.00027 0.00027 0.00027 0.00027 0.000017 . 0.000017 0.000018 0.000018 0.00027 0.00027 0.00026 0.00026 0.00026 0.00026 0.00026 0.00026 0.000019 0.000019 0.000020 0.000020 0.000021 0.000021 0.000022 0.000023 0.00026 0.00026 0.00026' 0.00026 0.000023 0.000024 0.000025 0.000026 0.00026 0.00026 0.00026 0.00026 0.000027 0.000028 0.000029 0.000030 0.00026 0.00025 0.00025 0.00025 0.000031 0.000032 0.000033 0.000034 0.00025 0.00025 0.00024 0.00024 0.000036 0.000037 0.000039 0.000040 0.00024 0.00024 0.00024 0.00024 0.000042 0.000043 0.000045 0.000047 0.00024 0.00024 0.00024 0.00024 0.000049 0.000051 0.000053 0.000055 - Approximate average decrease in weight per 0.1 F rise in dry-bulb temperature equals 0.000017 lb per cubic foot. pound of dry air. Since most air conditioning processes are of the steady flow type in which the thermal energy convected with the fluid , is its enthalpy, the third is most simply expressed in terms of enthalpy per pound of dry air. It is clear, therefore, that humidity ratio W and en thalpy per pound of dry air h are fundamental coordinates. Their use for the purpose of graphical representation is due to Mollier [3]. A convenient modification of the Mollier diagram devised by Goff is obtained by taking humidity ratio W as ordinate and reduced enthalpy {h -- 1000W) as abscissa, as shown in the chart enclosed in the envelope attached to the inside back cover of this book. The reasons for the use of the difference (h -- 1000WO as abscissa instead of h itself in the Mollier Diagram for Moist Air are the following: f \ ? 1 Thermodynamics of Air and Water Mixtures (1) it amounts to plotting on oblique coordinates and thus reduces to convenientproportions.a.diagram which would otherwise take the form of a scroll; (2) by the choice of the factor 1000 the "necessary'multiplication-----------reduces to shifting the .decimal point; (3) the ease with which the ordinate W can be multiplied by 1000 and added to the abscissa to obtain the enthalpy h makes it unnecessary to complicate the chart by a family of isenthalpic lines. In the Mollier diagram, the lines inclined upward and slightly to the right are lines of constant (dry-bulb) temperature. They are straight under Dalton's Law but actually have slight curvature. The lines in clined upward to the left are lines of constant thermodynamic wet-bulb and are straight by definition. The dry-bulb and wet-bulb lines meet at the saturation curve and coincide in the region to the left of this curve. This region is divided into three sub-regions by the narrow wedge with apex at the junction of the 32 F wet-bulb and dry-bulb lines. Above the wedge, the mixture consists of two distinct phases, saturated vapor and saturated liquid. At point A, for example, the temperature is 60 F and the vapor phase contains 0.01103 lb of water vapor per pound of dry air from Table 6. From the Mollier diagram, W = 0.016 lb, leaving 0.00497 lb per pound dry air in the liquid phase. The total enthalpy of the mixture is 10.51 + (1000 X 0.016) = 26.51 Btu per pound dry air of which 15.34 + (1000 X 0.01103) = 26.37 Btu per pound dry air is contributed by the vapor phase. Within the wedge, the mixture consists of three distinct phases, satu rated vapor, saturated solid and saturated liquid. The temperature is 32 F; and the relative proportions of the three phases depend upon the location of the state point within the wedge. Below the wedge, the mix ture consists of saturated vapor and saturated solid. The curved lines in the single vapor-phase region to the right of the saturation curve are lines of constant per cent saturation. Lines of contant dew-point are> of course, horizontal straight lines of constant cn'r'1 rat*- At point B, for example, the dry-bulb temperature is ou r, the thermodynamic wet-bulb is 50 F, the dew-point is 40.8 F, the degree of saturation is 48.6 per cent, the humidity ratio is 0.00536 lb per pound dry air, and the enthalpy is 14.85 + (1000 X 0.00536) = 20.21 Btu per pound dry air. With the aid of the Mollier diagram, it is easy to throw the definition ot thermodynamic wet-bulb, Equation 20, into a more familiar form. Consider the three points 1, 2, 3, Fig. 2. Point 3 is located with respect