The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U<sub>0</sub> = 400 W/m<sup>2</sup>.K. The fouling factor after one year of operation is found to be h<sub>d0</sub> = 2000 W/m<sup>2</sup>.K. The overall heat transfer co-efficient at this time is

Correct Answer: 333 W/m<sup>2</sup>.K