The only change in enthalpy is that from the heat content of the makeup water. Since the spray water enters at the wet- bulb temperature of 70 F and there is no heat added to or removed from it, this is by definition an adiabatic process and there will be no change in wet- bulb temperature. The leaving dry- bulb temperature is obtained directly from Fig. Figure 12-8 shows the path on a psychrometric chart.
To convert British thermal units per pound dry air- degree Fahrenheit to joules per Idlogram-kelvin, multiply by 4186.8 and to convert cubic feet per pound to cubic meters per kilogram, multiply by 0.0624. 12-2 Psychrometric chart-medium temperatures. Reading directly from the psychrometric chart (Fig. Įxamples Illustrating Use of Psychrometric Charts In these examples the following nomenclature is used.
ASHRAE PSYCHROMETRIC CHART SEA LEVEL TRIAL
By trial and error, = 72.1 F, or the adiabatic-saturation temperature is 0.1 F higher than the wet-bulb temperature. Values of andt, are given by the saturation curve of the psychrometric chart, such as Fig. Zimmerman and Lavine, Psychrometric Charts and Tables, Industrial Research Service, 2d ed., Dover, N.H., 1964. Treybal, Mass-Ttansfet- Operations, 3d ed. Quinn, Humidity The Neglected Parameter, Test Eng. Heating, Refrigerating and Air- Conditioning Engineers, New York, 1967. Figure 2 is a standard chart for water vapor in air (6). The effect of a dryer s atmospheric vapor content and temperature on performance can be studied by constmction of a psychrometric chart for the particular gas and vapor. īefore drying can begin, a wet material must be heated to such a temperature that the vapor pressure of the contained Hquid exceeds the partial pressure of vapor already present in the surrounding atmosphere.
The constmction of such has been considered (54). Eor these kinds of appHcations psychrometric charts for systems other than air-water would be useful. In the area of reactor studies there has been much interest in monolithic and honeycomb catalytic reactions (52,53) (see Exhaust control, industrial). In the adsorption area the separation of multicomponent fluid mixtures is influenced by comparative rates of diffusion and by interface temperatures (50,51). Drying simulation (45-47) and drying of foods (48,49) have been particularly active subjects. Work in the area of simultaneous heat and mass transfer has centered on the solution of equations such as 1-18 for cases where the stmcture and properties of a soHd phase must also be considered, as in drying (qv) or adsorption (qv), or where a chemical reaction takes place. Offices, homes, schools, shops, theaters, and many other appHcations are covered by this specification.
A wide range of environmental appHcations is covered by ASHRAE Comfort Standard 55 (5). Eigure 3 appHes generally to altitudes from sea level to 2150 m and to the common case for indoor thermal environments where the temperature of the surfaces (/) approximately equals air temperature (/ and the air velocity is less than 0.25 m/s. These zones should provide acceptable conditions for room occupants wearing typical indoor clothing who are at or near sedentary activity. To convert kj to kcal, divide by 4.184.Įigure 3 shows the winter and summer comfort zones plotted on the coordinates of the ASHRAE psychrometric chart.
Psychrometric chart at atmospheric pressure, 101.3 kPa (1 atm)(3). AH mass properties ate related to the mass of the dry air. Similar charts exist for temperatures below 0☌ and above 50☌ as well as for other barometric pressures. The properties of moist air are frequentiy presented on psychrometric charts such as that shown ia Figure 2 for the normal air conditioning range at atmospheric pressure. Psychrometrics is the branch of thermodynamics that deals specifically with moist air, a biaary mixture of dry air and water vapor. Using mass transfer rate, the heat transfer at equlibrium can be written as Įquation 11.7 shows how wet bulb temperature is dependent on humidity and temperature.