A heat exchanger is to be used to heat a process liquid within the tubes using saturated steam at 100ºC. The tubes have an inside diameter of 20 mm and outside diameter of 22 mm. It is estimated that the inner surface heat transfer coefficient will be 4.2 kW m^-2 K^-1 and the outer surface heat transfer coefficient will be 15.4 kW m^-2 K^-1 when the exchanger is clean. In order to allow for possible fouling during use you should assume a fouling factor of 1.12 × 10-4 m² K W^-1 will be applicable.

Estimate:

(i) the overall heat transfer coefficient in use

(ii) the heat transfer rate when the relevant average temperature difference between steam and fluid is 50ºC and the heat exchanger has 100 tubes each of 5 m in length.