INFLUENCE OF DISSIPATIVE ENTRY TEMPERATURE ON LAMINAR HEAT TRANSFER IN THERMALLY DEVELOPING REGION OF A CIRCULAR PIPE WITH VISCOUS DISSIPATION

Steady laminar forced convection heat transfer in the thermal entrance region of a circular pipe including viscous dissipation has been studied assuming the flow to be hydrodynamically fully developed and thermally developing. The circular pipe is subjected to constant wall temperature. Two entry temperatures have been considered. 1) A temperature that varies with the radial coordinate obtained in an adiabatic pipe due to viscous dissipation while the flow is hydrodynamically developing. This temperature is termed as the dissipative entry temperature. 2) A uniform temperature equal to the bulk mean value of the dissipative entry temperature. It has been shown that the difference in the Nusselt numbers and heat transfer obtained with these two entry temperatures is insignificant. Thus, the simplicity of classical assumption of uniform entry temperature can be retained when the entry temperature has been chosen as the bulk mean of the dissipative entry temperature