Question

Overall heat transfer coefficient is used in case of conduction

Answer 1

difference in temperature between the solid surface and surrounding fluid area, K. It is used in calculating the heat transfer, typically by convection or phase transition between a fluid and a solid. The heat transfer coefficient has SI units in watts per squared meter kelvin: W/(m2K).

Answer 2

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The heat transfer coefficient or film coefficient, or film effectiveness, in thermodynamics and in mechanics is the proportionality constant between the heat flux and the thermodynamic driving force for the flow of heat (i.e., the temperature difference, ΔT):

The overall heat transfer rate for combined modes is usually expressed in terms of an overall conductance or heat transfer coefficient.

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