Page:Journal of the American Society of Mechanical Engineers, Volume 33.pdf/668

[20]

$e=e'-{\frac {C_{pa}(P-e')(t-t')}{S'R'}}$

For $r'$ may be substituted the approximate value $r'=1091.6-0.56t'$ and for $S'$ the value $S'=0.6215+0.000034t'$ (approximately). Hence

[21]

$e=e'-{\frac {C_{pa}(P-e')(t-t')}{0.6215+0.000034t')(1091.6-0.56t')}}$

[22]

$e=e'-{\frac {C_{pa}(P-e')(t-t')}{678.4-0.3011t'}}$

TABLE 2 COMPARISON OF NEWLY DETERMINED PSYCHROMETRIC VALUES WITH OLD UNITED STATES WEATHER BUREAU VALUES

Water Vapor Containd in 1 Lb. of Pure Air for Wet Bulb of 60 Deg. Fahr. and Dry Bulb of $t$ from U. S. Weather Bureau Fomulæ												Water Vapor Actually Contained in 1 Lb. of Pure Air for Wet Bulb of 60 Deg. Fahr.
$t$		$t-t'$		$e$		$29.92-e$		Grain per Lb. Air		Per Cent Error		$t$		$t-t'$		$C_{ps}$		$C_{pa}$		Grain per Lb. Air
70		10		0	.4053	29	.515	59	.8	0	.0205	70		10		0	.4540	0	.24170	61	.06
75		15		0	.3495	29	.570	51	.5	0	.0280	75		15		0	.4544	0	.24172	52	.98
80		20		0	.2936	29	.625	43	.1	0	.0388	80		20		0	.4549	0	.24175	44	.84
85		25		0	.2380	29	.682	34	.9	0	.0548	85		25		0	.4553	0	.24177	38	.915
90		30		0	.1820	29	.738	26	.6	0	.0808	90		30		0	.4558	0	.24179	28	.934
95		35		0	.1260	29	.794	18	.4	0	.1238	95		35		0	.4662	0	.24181	20	.995
100		40		0	.0700	29	.850	10	.2	0	.2200	100		40		0	.4667	0	.24184	13	.082
105		45		0	.0145	29	.905	2	.11	0	.5960	105		45		0	.4571	0	.24187	5	.220
$e=$			$e'-0.00367P(t-t')\left(1+{\frac {t'-32}{1571}}\right)$									$G'=$				$77.32{\text{grains per lb.}}$
												$t'=$				$60{\text{deg. fahr}}$
$G=$			${\frac {e\times 0.6221\times 7000}{29.29-e}}$									$r'=$				$1057.8$
												$C_{ps}=$				$0.4423+0.00018t_{m}$
$t=$			${\text{dry-bulb temperature, deg. fahr}}$									$C_{pa}=$				$0.24112+0.000009t_{m}$
$C_{pa}=$			${\text{specific heat of air}}$									$G=$				${\frac {G'r'-7000C_{pa}(t-t')}{r'+C_{ps}(t-t')}}$
$c_{ps}=$			${\text{specific heat of vapor}}$

and if Swann’s value of $0.24112+0.000009t$ is accepted for the value of $C_{pa}$ as in the charts,

[23]

$e=e'-{\frac {(P-e')(t-t')}{2803-1.329t'}}$

This equation has been carefully tested by comparing with values of the psychrometric coefficient as determined by means of the