A feedwater heater that supplies a boiler consists of a shell-and-tube heat exchanger with one shell pass and two tube passes. One hundred thin-walled tubes each have a diameter of 20 mm and a length (per pass) of 2 m. Under normal operating conditions water enters the tubes at 10 kg/s and 290 K and is heated by con- densing saturated steam at 1 atm on the outer surface of the tubes. The convection coefficient of the saturated steam is 10,000 W/m2 · K.
(a) Determine the water outlet temperature.
(b) With all other conditions remaining the same, but accounting for changes in the overall heat transfer coefficient, plot the water outlet temperature as a function of the water flow rate for 5 mc 20 kg/s.
(c) On the plot of part (b), generate two additional curves for the water outlet temperature as a func- tion of flow rate for fouling factors of R"f 0.0002 and 0.0005 m2 · K/W.