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Heat Transfer - Engineering

Q1:

Overall heat transfer co-efficient of a particular tube is U1. If the same tube with some dirt deposited on either side has coefficient U2, then

A U1 = U2

B U2 > U1

C U1 > U2

D U1 = dirt factor - U2

ANS:A - U1 = U2

When dirt is deposited on either side of a tube, it typically reduces the overall heat transfer coefficient. Therefore: U2​<U1​ Explanation:

  • The overall heat transfer coefficient (U) represents the combined resistance to heat transfer on both the fluid side and the tube side of the heat exchanger.
  • When dirt accumulates on the tube surface, it creates an additional layer of thermal resistance, reducing the overall heat transfer coefficient.
  • The presence of dirt increases the thermal resistance, making it more difficult for heat to transfer through the tube wall and between the fluid and the tube surface.
  • As a result, the overall heat transfer coefficient U2​ with dirt deposited on the tube is lower than the original coefficient U1​.
Therefore, the correct statement is: U1​>U2​