Abstract
Numerical solutions for conjugate heat transfer of a hydro-dynamically fully developed, thermally developing, steady, incompressible laminar gas flow in a microtube with uniform wall heat flux boundary condition are presented. The mathematical model takes into account effects of rarefaction, viscous dissipation, flow work, shear work, and axial conduction in both the wall and the fluid. The effect of the tube wall thickness, the wall-to-fluid thermal conductivity ratio, as well as other factors on heat transfer parameters is investigated, and comparisons with the case of zero wall thickness are presented as appropriate. The results illustrate the significance of heat conduction in the tube wall on convective heat transfer and disclose the significant deviation from those with no conjugated effects. Increasing the wall thickness lowers the local Nusselt number. Increasing the wall-to-fluid thermal conductivity ratio also results in lower Nusselt number. In relatively long and thick microtubes with high wall-to-fluid thermal conductivity ratio, the local Nusselt number exhibits minimum values in the entrance regions and at the end sections due to axial conduction effects. The analysis presented also demonstrate the significance of rarefaction, shear work, axial conduction, as well as the combined viscous dissipation and flow work effects on heat transfer parameters in a microtube gas flow. The combined flow work and viscous dissipation effects on heat transfer parameters are significant and result in a reduction in the Nusselt number. The shear work lowers the Nusselt number when heat is added to the fluid.
