Document gD3Qm9xzD5ad3XZM6nEEwa9ZV

HEATINC VENTILATING AIR CONDITIONING GUIDE 1942 Table 9. Weight of Saturated and Partly Saturated Air3 Dbt-Bulb Temp Dbg F 28.5 Weight op Saturated Air fob 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 Deg Wet-Bulb Depression 30 0.07703 0.07839 0.07974 0.08110 0.08245 0.08381 0.00027 0.000017 32 0.07671 0.07806 0.07940 0.08075 0.08210 0.08345 0.00027 0.000017 34 0.07638 0.07772 0.07907 0.08041 0.08175 0.08310 0.00027 0.000018 36 0.07605 0.07739 0.07873 0.08007 0.08141 0.08274 0.00027 0.000018 38 0.07573 0.07706 0.07840 0.07973 0.08106 0.08239 0.00027 0.000019 40 0.07541 0.07674 0.07806 0.07939 0.08072 0.08205 0.00027 0.000019 42 0.07509 0.07641 0.07773 0.07905 0.08038 0.08170 0.00026 0.000020 44 0.07477 0.07609 0.07740 0.07872 0.08004 0.08135 0.00026 0.000020 46 0.07445 0.07576 0.07707 0.07838 0.07970 0.08101 0.00026 0.000021 48 0.07413 0.07544 0.07674 0.07805 0.07936 0.08066 0.00026 0.000021 50 0.07381 0.07512 0.07642 0.07772 0.07902 0.08032 0.00026 0.000022 52 0.07350 0.07479 0.07609 0.07739 0.07868 0.07998 0.00026 0.000023 54 0.07318 0.07447 0.07576 0.07706 0.07835 0.07964 0.00026 0.000023 56 0.07287 0.07415 0.07544 0.07673 0.07801 0.07930 0.00026 0.000024 58 0.07255 0.07383 0.07512 0.07640 0.07768 0.07896 0.00026 0.000025 60 0.07224 0.07352 0.07479 0.07607 0.07734 0.07862 0.00026 0.000026 62 0.07193 0.07320 0.07447 0.07574 0.07701 0.07828 0.00026 0.000027 64 0.07161 0.07288 0.07414 0.07541 0.07668 0.07794 0.00026 0.000028 66 0.07130 0.07256 0.07382 0.07508 0.07634 0.07760 0.00026 0.000029 68 0.07098 0.07224 0.07350 0.07475 0.07601 0.07727 0.00026 0.000030 70 0.07067 0.07192 0.07317 0.07442 0.07568 0.07693 0.00026 0.000031 72 74 0.07035 0.07160 0.07285 0.07410 0.07534 0.07659 0.00025 0.000032 0.07004 0.07128 0.07252 0.07377 0.07501 0.07625 0.00025 0.000033 76 0.06972 0.07096 0.07220 0.07343 0.07467 0.07591 0.00025 0.000034 78 0.06940 0.07064 0.07187 0.07310 0.07434 0.07557 0.00025 0.000036 80 0.06909 0.07032 0.07155 0.07277 0.07400 0.07523 0.00025 0.000037 82 0.06877 0.07000 0.07122 0.07244 0.07366 0.07489 0.00024 0.000039 84 0.06845 0.06967 0.07089 0.07211 0.07333 0.07454 0.00024 0.000040 86 0.06812 0.06934 0.07056 0.07177 0.07299 0.07420 0.00024 0.000042 88 0.06780 0.06901 0.07022 0.07143 0.07264 0.07385 0.00024 0.000043 90 0.06748 0.06868 0.06989 0.07109 0.07230 0.07351 0.00024 0.00004S 92 0.06715 0.06835 0.06955 0.07075 0.07195 0.07316 0.00024 0.000047 94 0.06682 0.06801 0.06921 0.07041 0.07161 0.07280 0.00024 0.000049 96 0.06648 0.06768 0.06887 0.07006 0.07126 0.07245 0.00024 0:000051 98 0.06615 0.06734 0.06853 0.06972 0.07091 0.07209 0.00024 0.000053 100 0.06581 0.06700 0.06818 0.06937 0.07055 0.07174 0.00024 0.000055 Approximate average decrease in weight per 0.1 F rise in dry-bulb temperature equals 0.000017 lb per cubic foot. 26 CHAPTER I. THERMODYNAMICS OF AIR AND WATER MIXTURES 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 con stant dew-point are, of course, horizontal straight lines of constant humidity ratio. At point B, for example, the dry-bulb temperature is 60 F, 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 of 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 to points 1 and 2 so that W3 -- Wi and t3 = k- Points 1 and 2, being on a line of constant thermodynamic wet-bulb, satisfy Equation 20;.thus,. h - ht + (W, - Wi) h'w>1 = h, - h, where h3 has been subtracted from both sides. Under Dalton's Law, fh -- h3 = Wi) Aw,2; moreover, hi -- h3 may be replaced by Ji Ch -- k) where Si is often referred to as mean, humid heat and may be calculated with good approximation from = 0.240 + 0.444 Wi (21) Finally, introducing latent heat of vaporization at the wet-bulb tempera ture, namely, (ftfg)2 = (h^, -- Equation 20 becomes, after omitting the subscript 2, <i -- t' _ his Ws - Wi T, (22) it being understood that Ws is the saturation humidity ratio and hts, the latent heat, at the wet-bulb temperature t'. Equation 22 was derived by Carrier [1].. Example IS. Work Example 10 using Equation 22. Solution. A trial-by-error method is involved. Taking 48 F as a trial value of (80 - 48) -l- (0.007072 - 0) = 4520; but 1066.7 -i- 0.240 = 4440. The trial value must, therefore, be revised upward, the final solution being 48.26 F as in Example 10. 27