Numerical Prediction of a Bi-Directional Micro Thermal Flow Sensors

Thermal flow sensors such as hot-wire anemometer (HWA) can be used to measure the flow velocity with certain accuracy. However, HWA can measure the flow velocity without determining the flow direction. Pulsed-Wire Anemometer (PWA) with 3 wires can be used to measure flow velocity and flow directions. The present study aims to develop a numerical analysis of unsteady flow around a pulsed hot-wire anemometer using three parallel wires. The pulsed wire which is called the heated wire is located in the middle and the two sensor wires are installed upstream and downstream of the pulsed wire. 2-D numerical models were built and simulated using different wires arrangements. The ratio of the separation distance between the heated wire and sensor wire (x) to the diameter of the heated wire (D) ratios (x/D) was varied between 3.33 and 183.33. The output results are plotted as a function of Peclet number (convection time / diffusion time). It was found that as the ratio of x/D increases, the sensitivity of PWA device to the time of flight decreases. But at the same the reading of the time of flight becomes more accurate, because the effects of the diffusion and wake after the heated wire decrease. Also, a very good agreement has been obtained between the present numerical simulation and the previous experimental data.