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The derivation of Log Mean Temperature Difference (LMTD) for a Heat exchanger at preliminary level makes some assumptions like, constant specific heats, steady state operation, no changes in kinetic and potential energies, constant overall heat transfer coefficient. I wanted to know whether the inner tube wall temperature is also assumed constant in the radial direction for deriving the LMTD relation or not.

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  • $\begingroup$ The driving force for heat transfer is a temperature difference. What does that tell you? $\endgroup$ Mar 18, 2021 at 16:17
  • $\begingroup$ it is assumed constant with time (steady state operation) in the radial direction, but not along the axial direction. $\endgroup$ Mar 18, 2021 at 17:34

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No, the temperature varies in radial direction within the tube wall of heat exchanger.

While deriving the LMTD (Log Mean Temperature Difference) for heat exchanger, the heat transfer along the tube axis is assumed to be negligible while the heat transfer between hot and cold fluids is considered in radial direction through the tube wall therefore there exists a radial temperature gradient within the tube wall.

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