Air-Water Mixtures—Enthalpies and Humidities

Air saturated 65°F (65°F wet-bulb) has an enthalpy of Hls = 30.4 Btu/lb air at the outlet temperature of 80°F (value interpolated from Table 5.4). This is the exit conditions of the tower and thus represents one endpoint on the operating line (point C). The liquid and air loadings determine the slope of the operating line starting at point C  

SHADED REGION DENOTES HEAT TRANSFER POTENTIAL 

Hence we can locate the other endpoint of the operating line, point D (118°F, 65.1 Btu/lb-air). 

The area bound between the saturation line and the operating line is proportional to the potential for heat transfer. We now have two choices on how to obtain the final solution (Ntu ) a graphical or numerical solution. Each is outlined below  

By numerical integration we can use Simpson s rule to evaluate the data in columns 1 and 5 of Table 5.5. 

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