For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus- Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of________________?

Correct answer: C. 6.1

  • A. 1
  • B. 1.74
  • C. 6.1
  • D. 37

Explanation

With constant properties and doubled volumetric flow, halving the diameter makes velocity increase eightfold, so Reynolds number increases fourfold. Since h is proportional to Re^0.8/D, the factor is 4^0.8 × 2 ≈ 6.1.

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