Psychrometric chart for air

FIG. 12-5 Revised form of high-temperature psychrometric chart for air and combustion products, based on pound-moles of water vapor and dry gases. [Hatta, Chem. Metall. Eng., 37, 64 (1930).]... 

This reduces to Y, 0.0864 — 10.194 X 10 , which must be solved simultaneously with the saturated-humidity curve of the psychrometric chart for air-water vapor. The line marked a on... 

FIG. T-54 Psychrometric chart for air inlet saturating condition. (Source Staider.)... 

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. Drying simulation (45—47) and drying of foods (48,49) have been particularly active subjects. In the adsorption area the separation of multicomponent fluid mixtures is influenced by comparative rates of diffusion and by interface temperatures (50,51). In the area of reactor studies there has been much interest in monolithic and honeycomb catalytic reactions (52,53) (see Exhaust control, industrial). Eor these kinds of appHcations psychrometric charts for systems other than air—water would be useful. The constmction of such has been considered (54). 

Before 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 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. Figure 2 is a standard chart for water vapor in air (6). 

Figure B-2. Psychrometric chart atmospheric air, mixture pressure (barometric) 29.921 in. Hg. (From Short, Kent and Walls, Pressure-Enthalpy Otarts for Selected Engineering Substances. Gulf Publishing Company, Houston, TX, 1970.)...

To calculate the cooling requirement for 1000 ft /min of delivered air. we must first determine the volume of delivered air corresponding to our assumed basis and scale the calculated value of Q by the ratio (1000 fp/min)/ (Vbasis)- From the psychrometric chart, for humid air saturated at 51°F... 

The psychrometric chart for most gas-liquid systems would show a family of adiabatic saturation curves in addition to the families of curves shown on Figures 8.4-1 and 8.4-2. However, for the air-tvater system at 1 atm, the adiabatic saturation curve through a given state coincides with the constant wet-bulb temperature line through that state, so that Tas = Twb- The simple material and energy balance procedure for adiabatic cooling outlined in this section is possible only because of this coincidence. 

Fig. 5 Psychrometric chart for an air-water system at a total pressure of 760mmHg.

FIG. 12-1 Grosvenor psychrometric chart for the air-water system at standard atmospheric pressure, 101,325 Pa, SI units. (Courtesy Carrier Corporation.)... 

Figure 12-4 shows a psychrometric chart for combustion products in air. The thermodynamic properties of moist air are given in Table 12-1. Figure 12-4 shows a number of useful additional relationships, e.g., specific volume and latent heat variation with temperature. Accurate figures should always be obtained from physical properties tables or by calculation using the formulas given earlier, and these charts should only be used as a quick check for verification. 

Figure 23.1 is a psychrometric chart for the air-water system. It shows the relationship between the temperature (abscissa) and absolute humidity (ordinale, in g water per kg dry air) of humid air from 0°C to 130°C at one atmosphere absolute pressure. Line as representing percent humidity and adiabatic saturation are drawn according to the thermodynamic definitions of these terms. Equations for the adiabatic saturation and wet-bulb temperature lines on the chart are as follows (Geankoplis 1983) ... 

Psychrometrics. Psychrometrics is the branch of thermodynamics that deals specifically with moist air, a biaary mixture of dry air and water vapor. 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. Similar charts exist for temperatures below 0°C and above 50°C as well as for other barometric pressures. AH mass properties ate related to the mass of the dry air. 

Eigure 3 shows the winter and summer comfort zones plotted on the coordinates of the ASHRAE psychrometric chart. These zones should provide acceptable conditions for room occupants wearing typical indoor clothing who are at or near sedentary activity. 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. A wide range of environmental appHcations is covered by ASHRAE Comfort Standard 55 (5). Offices, homes, schools, shops, theaters, and many other appHcations are covered by this specification. 

Figures 12-37 to 12-39 show humidity charts for carbon tetrachloride, oenzene, and toluene. The lines on these charts have been calculated in the manner outlined for air-water vapor except for the wet-bulb-temperature lines. The determination of these hnes depends on data for the psychrometric ratio /j Z/c, as indicated by Eq. (12-22). For the charts shown, the wet-bulb-temperature hnes are based on the following equation ...

Psychrometric charts plot wet bulb and dry bulb data for air-water vapor mixtures at atmospheric pressure. These charts are quite useful for... 

The study of moist air. The psychrometric chart shows the relationship between the various properties of moist air in graphical form and can be used for the solution of problems. 

When two samples of air are brought together the condition of the mixture may be arrived at arithmetically by adding the heat flow of each and dividing by the total mass flow and similarly for the moisture flow. Alternatively, plot the condition of each onto a psychrometric chart. The mixed condition lies on a straight line between the two in a position proportional to the two quantities. 

Make no excuse for checking whether the sun shines on the thermostats or someone has washed the floor. Another common occurrence is that while the room is not being controlled as specified, the plant appears to be operating correctly. Here a series of simultaneous readings of air flows and wet and dry bulb temperatures should be taken around the whole of the air circuit - on and off coil, condition after fan, condition at inlet grilles, etc. Referring these to a psychrometric chart will usually indicate where the fault or leak lies. 

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