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 ”

“ Moreover, recent investigators conducting their experiments with modern apparatus, supposedly with extreme accuracy, differed from each other by more than 3 per cent, and from the generally accepted value of Regnault, by more than 2 per cent. Therefore, in order to use a rational formula in the construction of accurate psychrometric charts and tables, it becomes necessary to determine the specific heat of air to a much greater degree of accuracy than is known at present. ”

“ Two fans are required. Fan No. 1 draws the air through moist sponge A. The air in passing through the fan rises in temperature so that it is desirable to saturate it further by passing it through a moist sponge filter B. The wet and dry-bulb temperatures of the air are then taken with thermometers 1 and 2. These readings should be practically identical so that error in calculating the true dew point is negligible. The air is then heated by passing it through an electric heater provided with a rheostat for regulating the temperature. ”

“ However, considering the difficulties of their experimental method and the correction necessary for radiation in the wet-bulb reading, the results obtained are remarkable for consistency and accuracy. There are errors in the form of the equation, however, as well as in the constants employed, which make its inaccuracy more pronounced at lower humidities and at the higher temperature. At very high temperatures used in mechanical drying it is entirely inoperative.
59⁠The need of an accurate rational psychrometric formula for vapor pressures using modern data is therefore apparent. ”

“ This error has been taken as directly proportional to the depression. More accurately it is proportional to the difference of the fourth powers of the respective absolute temperatures, except for the stem correction. ”

“ A specialized engineering field has recently developed, technically known as air conditioning, or the artificial regulation of atmospheric moisture. The application of this new art to many varied industries has been demonstrated to be of greatest economic importance. ”

“ If the air became drier, it would evaporate moisture from the solution, increasing its density. If, on the other hand, the humidity of the air increased, moisture would be absorbed by the solution until it reached an equilibrium.
17⁠A test was made by the writer in May 1902, to determine the moisture-absorbing properties of calcium-chloride brine for the purpose of air conditioning. ”

“ In this type of psychrometer it should be noted that the impact of the air upon the thermometer bulbs largely neutralizes the reduction in pressure, producing the velocity as demonstrated in experiment No. 1.
82⁠Experiment No. 3. The purpose of this experiment was to demonstrate principles C and D in Pars. 30 and 31. A modified form of the evaporation calorimeter as shown in Figs. 5 and 6 was used.“ The air was first passed through two layers of moistened sponge, bringing it very close to true
Fig. ”

“ Therefore, the dew point may be defined as the minimum temperature to which air of a given moisture content may be cooled without precipitation of moisture.
9⁠Usually it is more convenient to determine the absolute and relative humidities from the temperature-pressure curve by comparing the vapor pressures. The per cent of humidity is , but it may also be shown to be equal to ; i.e.
[1]
where , is the pressure of saturated vapor corresponding to the dew point , and is the vapor pressure at saturation corresponding to temperature . ”

“ In many other industries, such as lithographing, the manufacture of candy, bread, high explosives and photographic films, and the drying and preparing of delicate hygroscopic materials, such as macaroni and tobacco, the question of humidity is equally important. ”

“ However, if water vapor, or air containing water vapor, having a temperature , and an absolute humidity of , be cooled to , it will become saturated, and if cooled further, moisture will be precipitated. Therefore is termed the dew point of air having a temperature and an absolute humidity, , or a corresponding relative humidity, . ”

“ When applied to the blast furnace, it has increased the net profit in the production of pig iron from $0.50 to $0.70 per ton, and in the textile mill it has increased the output from 5 to 15 per cent, at the same time greatly improving the quality and the hygienic conditions surrounding the operative. ”

“ By either of these two methods, given in Appendix No. 4, the relations of formula [6] are established.
6
in which
= the true wet-bulb depression = the moisture absorbed per lb. of pure air when it is adiabatically saturated from an initial dry-bulb temperature and an initial moisture content = mean specific heat of air at constant pressure between temperature and = specific heat of steam at constant pressure between and = latent heat of evaporation at wet-bulb temperature Knowing any two of the three important values of , or , we may solve for the third or for any other required relation. ”