Asked in a 2000 paper

The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m2.K. The fouling factor after one year of operation is found to be hd0 = 2000 W/m2.K. The overall heat transfer co-efficient at this time is _____________________?

Correct answer: C. 333 W/m2.K

  • A. 1200 W/m2.K
  • B. 894 W/m2.K
  • C. 333 W/m2.K
  • D. 287 W/m2.K

Explanation

Add the fouling resistance to the clean exchanger resistance: 1/U = 1/400 + 1/2000 = 0.003 m²·K/W. Thus U is approximately 333 W/m²·K, showing why fouling lowers the overall coefficient.

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