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Heat Transfer - Engineering

Q1:

In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid

A varies directly as the area and the LMTD.

B directly proportional to LMTD and inversely proportional to the area.

C varies as square of the area.

D none of these.

ANS:A - varies directly as the area and the LMTD.

In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid varies directly as the area and the LMTD (Log Mean Temperature Difference). The rate of heat transfer (Q) in a heat exchanger is given by the following equation: lmQ=U⋅A⋅ΔTlm​ where:

  • Q is the rate of heat transfer,
  • U is the overall heat transfer coefficient,
  • A is the heat transfer area, and
  • lmΔTlm​ is the log mean temperature difference.
This equation indicates that the rate of heat transfer is directly proportional to both the area (A) and the log mean temperature difference (lmΔTlm​). Therefore, the correct statement is: varies directly as the area and the LMTD.