Water enters a circular tube whose walls are maintained at constant temperature at specified flow rate and temperature. For fully developed turbulent flow, the Nusselt number determined from Nu -0.023 can be law of cooling in this case is Re0.8 PrO.4. The correct temperature difference to use in Newton's (a) the difference between the inlet and outlet water bulk temperature (b) the difference between the inlet water bulk temperature and the tube wall temperature (o) the difference between the average water bulk temperature and the tube temperature (d) the log mean temperature difference (e) None of the above. Explain.

According to newton's law of cooling, log mean temperature difference must be used to determine the convective heat transfer in the tube when the surface of the tube is maintained at constant temperature. Log mean temperature represent the exact average temperature difference between the fluid and the surface. hence the answer is D the log mean temperature difference

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