Water at 0.8 kg/s enters the tubes of a two-shell-pass, four-tube-pass heat exchanger at 17°C and leaves at 37°C. It cools 0.5 kg/s of air entering the shell at 250°C with U = 432 W/ m 2 m 2 .K....

Water at 0.8 kg/s enters the tubes of a two-shell-pass, four-tube-pass heat exchanger at 17°C and leaves at 37°C. It cools 0.5 kg/s of air entering the shell at 250°C with U = 432 W/ m²
m².K. Determine : (a) the exit air temperature ; (b) the area of the heat exchanger ; and (c) the exit temperature if, after some time, the tubes become fouled with R_f
= 0.0005 m². K/W.