Low Peclet Gaseous Flows through Isothermally Heated Circular Pipe

Abstract

Conventional Graetz problem with the assumption of no axial conduction and property variation leads to erroneous determination of hydrodynamic and thermal flow fields. Slow gaseous flows subjected to imposed thermal boundary conditions require the temperature at the inlet to the heating zone to be solved for. Such low Peclet flows through tubes of circular cross-section subjected to constant wall temperature conditions is studied numerically in the present work. Different combinations of varying thermophysical properties and imposed wall temperatures are considered which allows us to obtain the actual heating length required for the fluid to attain wall temperature. The local and averaged Nusselt number is found to be a function of Peclet number and the supplied wall heat flux. The strength of axial conduction is found to be varying with axial and radial locations, leading to deviations of the standard correlations for the Nusselt number values.