Conjugate response of a thermal boundary layer with reverse flow

The full numerical solutions of the heat transfer from a flush mounted wall hot-film is carried to investigate its response in reversing flow by taking into account both the axial diffusion and the conduction to the substrate. It is shown that the axial diffusion affects considerably the heat transfer at the reversal points. The numerical results are in good agreement with the experiments conducted in an unsteady water channel. When the conductivity ratio of the substrate to the fluid is high, the response of the film is considerably attenuated, and it is hard to detect the flow reversal phase from the cyclic variations of the global heat flux. The direct flux from the film to the film is relatively less dependent on the conductivity ratio and follows reasonably well the flow reversal.