American Society of Mechanical Engineers

“ Weight of air = 1 lb. Specific weight of air = 1 = total barometric pressure in lb. per sq. ft. = weight of saturated water vapor in 1 lb. pure air = pressure of saturated water at given temperature , in lb.per sq. ft. = specific weight of water vapor at temperature , compared with air at same temperature and pressure ”

“ This, however, would have no effect upon the calculated absolute humidity, but only on the temperature and consequent relative humidity.
81⁠The type of psychrometer which lends itself to the most accurate determinations is the Aszmann aspiration psychrometer [1] shown in Fig. 14. Here the air is aspirated through two tubes containing the wet and dry-bulb thermometers. The wet-bulb temperature is brought to a minimum by the use of an atomizer. This serves also to moisten the inner surface of the enveloping tube, thus cooling it and preventing radiation. ”

“ The temperature of the liquid is evidently constant at temperature , from principle C. The total heat of the vapor in the increment is , where is the total heat of steam corresponding to temperature and vapor pressure , and is the heat required to superheat from saturation temperature to dry-bulb temperature . The heat of the liquid evaporated, however, is corresponding to temperature of saturation .
87 The total heat interchange required to evaporate under these conditions is therefore
[40]
The change in sensible heat of 1 lb. ”