AT-2804 -- A Friendly Microprocessor Approach to the Determination of the Thermodynamic Properties of Moist Air PDF

The determination of the explicit solution to the thermodynamic properties and moisture content of moist air from known values of dry-bulb and wet-bulb temperature has been available for some time. Computer codes have been written in FORTRAN and BASIC languages utilizing algorithms that permit the solution for the enthalpy and specific humidity of moist air from known input of dry-and wet-bulb temperature and barometric pressure of the air-water vapor mixture. As is often the case, dry-bulb temperature and relative humidity are known, and unless the program user wishes to consult a psychrometric or a wet-bulb depression chart to obtain wet-bulb temperature, the efficient use of a computer is circumvented and the solution to the problem is implicit, at best.

The objective of this paper is to present an algorithm for the determination of wet-bulb. By interacting with temperature as a function of dry-bulb temperature and relative humidity the microprocessor computer only, the user is able to determine enthalpy and specific humidity for the air-water vapor mixture and also account for the variation in these properties as a function of site altitude.