Applying the Exergy Balance: Control Volumes at

QUESTION:

Liquid water enters a heat exchanger operating at steady state at \(T_1\) = \(60^{\circ} \mathrm{F}\), \(p_1\) = 1 atm and exits at \(T_2\) = \(160^{\circ} \mathrm{F}\) with a negligible change in pressure. In a separate stream, steam enters at \(T_3\) = \(20 \mathrm{lbf} / \mathrm{in}^2\), \(x_3\) = 92% and exits at \(T_4\) = \(140^{\circ} \mathrm{F}\), \(p_4\) = 18 \(\mathrm{lbf} / \mathrm{in.}^2\) Stray heat transfer and the effects of motion and gravity are negligible. Let \(T_0\) = \(60^{\circ} \mathrm{F}\), \(p_0\) = 1 atm. Determine (a) the ratio of the mass flow rates of the two streams and (b) the rate of exergy destruction, in Btu per lb of steam entering the heat exchanger.