Effect of Axial Fluid Conduction on Heat Transfer in the Entrance Regions of Parallel Plates and Tubes

Abstract

The laminar heat transfer in thermal-entry regions of parallel plates and tubes is investigated for special conditions under which the contribution of axial fluid conduction is comparable to or greater than the axial convection (low Peclet numbers). Zero and finite axial-conduction solutions for the local and mean fluid temperature and the local total Nusselt number are presented for uniform-velocity flow, finite wall resistance, and for both a uniform ambient temperature and step discontinuity in the ambient temperature. Calculated mean fluid temperatures, local total Nusselt numbers, and thermal-entry lengths are compared with corresponding predictions for the conventional case of zero axial conduction.