Page:Journal of the American Society of Mechanical Engineers, Volume 33.pdf/663

$t+459.64$ = absolute temperature

$D_{s}$= density in lb. per cu. ft. of saturated water vapor at temperature $t$

= reciprocal of specific volume of steam

$P$ = 29.92 = assumed standard of barometric pressure in in. of mercury

$e$ = vapor pressure of saturated water vapor

$5284$ = constant of the equation

The derivation of equation [5] is given in Appendix No. 3.

TABLE 1 SPECIFIC WEIGHT OF STEAM

$S={\frac {53.35(t+450.0)D_{s}}{144x0.4008E}}$

$t$		$s$		$D_{s}$		$S$		$S$ Corrected		$D_{s}$ Corrected		Grains Moisture per cu. ft
40		0	.2477	0	.000410	0	.6345	0	.6228	0	.0004089	2	.8623
50		0	.3625	0	.000587	0	.6230	0	.6231	0	.0005871	4	.1697
60		0	.5220	0	.000828	0	.6221	0	.6223	0	.0006296	4	.4072
70		0	.7390	0	.001148	0	.6212	0	.6236	0	.0011524	8	.0668
80		1	.0290	0	.001570	0	.6217	0	.6239	0	.0015755	11	.0285
90		1	.1470	0	.002130	0	.6237	0	.6242	0	.0021820	14	.9240
100		1	.9260	0	.002851	0	.63525	0	.6246	0	.0028482	19	.9874
110		2	.5890	0	.003766	0	.6255	0	.6250	0	.0037630	28	.3410
120		3	.4380	0	.004924	0	.62665	0	.6254	0	.0049140	34	.3980
130		4	.5200	0	.006370	0	.6273	0	.6260	0	.0063570	44	.4990
140		5	.8800	0	.008140	0	.6266	0	.6266	0	.0081400	55	.9800
150		7	.5700	0	.070320	0	.6280	0	.6273	0	.0103100	72	.1700
160		9	.6500	0	.012960	0	.6282	0	.6280	0	.012955	90	.5920
170		12	.200	0	.016140	0	.6288	0	.6288	0	.016140	112	.9800
180		15	.290	0	.019940	0	.6296	0	.6298	0	.019940	139	.5800
190		19	.020	0	.024440	0	.6301	0	.6307	0	.024463	171	.2550
200		23	.47	0	.029760	0	.6313	0	.6316	0	.029780	208	.4600

47The specific weight of saturated water vapor is not constant, but varies with the temperature of saturation and may be calculated from equation [1]. The theoretical value, computed from its molecular weight, assuming it to be a perfect gas, is 0.6221. This is the assumption made in the computation of the psychrometric tables published by the United States Weather Bureau, which are inaccurate, therefore, in proportion to the variation of $S$ from this theoretical value. The actual values for the specific weight of water vapor at various saturation temperatures, computed from equation [35] are given in Table 1.