A micro flowmeter based on the velocity measurement of a locally accelerated thermal flow in an upwardly directed Hagen-Poiseuille flow

A simple measurement method of micro volumetric flow rate with high precision and low cost is proposed for industrial use. Poiseuille flow is obtained within a very short entrance length, especially for low Reynolds number flows. A locally accelerated thermal flow is produced by a small electric heater which is placed in the center part of an upwardly directed Poiseuille flow. It was found that the mean velocity of locally accelerated flow V-a between the heater and the thermal sensor, which accelerates the local maximum velocity of the base Poiseuille flow, is directly proportional to the volumetric flow rate Q(u) in a pipe within low Reynolds number flows. Q(v) can be obtained by using the linear relationship between V-a and Q(v). The validity of measuring the flow rate below 1 mL/min was confirmed for both water and air flows experimentally and numerically. Numerical simulation was performed using unsteady twodimensional Boussinesq equations in order to validate the measurement principle of this new micro flowmeter, and also to determine the optimized flowmeter design, such as the most suitable sensor position and the amount of joule heating. (C) 2008 Elsevier Ltd. All rights reserved.