Optimum design of microthermal flow sensor and its evaluation in wall shear stress measurement

A numerical analysis of unsteady conjugate heat transfer for a microthermal flow sensor was made in order to improve its frequency response in the wall shear stress measurement. It is found that there exists a limit of the frequency response even for the ideal sensor that has no heat conduction loss to the substrate. Heat conduction in the fluid and indirect convective heat transfer from the diaphragm are two major mechanisms of sensor response deterioration. We propose an optimum arrangement of the hot-film and diaphragm based on the detailed numerical simulation of the thermal field, and evaluate its performance in turbulent flow measurements.