Exergy Analysis of Reacting and Psychrometric SystemsFigure P13.114 provides data for a co...

Exergy Analysis of Reacting and Psychrometric Systems

Figure P13.114 provides data for a cooling tower at steady state. Using results from Problem 13.111 as needed, determine the rate of exergy destruction, in Btu/min. Let the environment be a mixture of dry air and water vapor at 90°F, 1 atm with . Also, let cpa = 0.24 Btu/lb · °R and cpv = 0.44 Btu/lb · °R.

Fig. P13.114

Problem 13.111

Exergy Analysis of Reacting and Psychrometric Systems

For psychrometric applications such as those considered in Chap. 12, the environment often can be modeled simply as an ideal gas mixture of water vapor and dry air at temperature T0 and pressure p0. The composition of the environment is defined by the dry air and water vapor mole fractions , , respectively.

(a) Show that relative to such an environment the total specific flow exergy of a moist air stream at temperature T and pressure p with dry air and water vapor mole fractions ya and yv, respectively, can be expressed on a molar basis as

where  and  denote the molar specific heats of dry air and water vapor, respectively. Neglect the effects of motion and gravity.

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(b) Express the result of part (a) on a per unit mass of dry air basis as

where  and