Shown in Fig. P10–118 is the tube layout for a horizontal condenser that is used for liquefying 900 kg/h of saturated ammonia vapor at 37°C. There are 14 copper tubes, each with inner diameter D_i = 3.0 cm and outer diameter D_o = 3.8 cm. A coolant flows through the tubes at an average temperature of 20°C such that it yields a heat transfer coefficient of 4.0 kW/m² · K. For this condenser, estimate

(a) The average value of the overall heat transfer coefficient.

(b) The tube length. Assume a tube outer surface temperature of 31°C. Is this a good assumption?

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