Question

Why does the heat transfer coefficient in circular tube with constant temperature decrease

Answer 1

In Newton's law of cooling, the heat transfer coefficient acts as a constant of proportionality. The relation Q = h.A. ΔT, which describes convective heat transfer suggests increase in the heat transfer rate at higher heat transfer coefficient values.

Convection is the bulk motion of a fluid, which may occur naturally or forcibly. In this mode, heat transfer is because of the mass transfer.

As our common sense suggests, more the velocity, more the rate of mass transfer and hence more is the rate of convective heat transfer.

Hence heat transfer coefficient increases with the increase in the velocity of the fluid.

The same thing can be proved by dimensional analysis.

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