A one-shell and two tube passes heat exchanger is constructed of stainless steel. The tube has an inner diameter of 1.5 cm and an outer diameter of 1.9 cm. The convective heat transfer coefficient on the inner surface of the tube (hi) is 800 Wm-2K -1 and the outer surface of the tube is (ho) is 1200 W.m-2K -1 . A thin fouling layer has developed over the years on the outer surface of the tube from the use of liquid refrigerant.

(a) Determine the total thermal resistance of the heat exchanger per unit length for each tube. [ANS: 0.046 k/W]

(b) Determine the overall heat transfer coefficients Ui and Uo based on the inner and outer surface areas of the tube, respectively. [ANS: Ui = 458.04 W/m2K , Uo = 361.61 W/m2K]

(c) This shell and tube heat exchanger is to be used to cool 0.2 kg s-1 of alcohol from 75 oC to 35 oC by flowing cooling water in the shell-side of the exchanger at 12oC and at a flow rate of 0.16 kg s-1 . Calculate the length of the heat exchanger required and comment on your answer. [ANS: 28.1m]