Numerical study of axial heat conduction effects on the local Nusselt number at the entrance and ending regions of a circular microchannel

The effects of duct wall thermal conductivity and thickness on the local Nusselt number at the entrance and ending regions of a circular cross-section microchannel in a conjugate heat transfer problem are numerically investigated. The simultaneously developing laminar flow with a constant heat flow rate per unit length on the outside surface of the duct wall is considered. The results show that the axial heat conduction in the duct wall decreases the local Nusselt number at the entrance and ending regions of the microchannel with respect to their values for microchannels without conjugate effects. The effects of various parameters on the local Nusselt number at the ending region of the microchannel are analyzed and three generalized correlations are proposed for predicting the ending length and corresponding local and average Nusselt numbers. Comparisons with other numerical results show suitable accuracy of the correlations.

► Local Nu at the ending region decreases from fully developed value.
► A correlation is presented for local Nusselt number at the ending region.
►  Another correlation is derived for the length of the ending region.
► A new dimensionless number is introduced as a parameter in correlations.