A micro flowmeter based on the measurement of a diffusion temperature rise of a locally heated thermal flow in a Hagen–Poiseuille flow

• A new micro volumetric flowmeter.
• Free and forced mixed convection.
• Measurement of a diffusion temperature rise.
• Qv≦1 mL/min for water flow.
• Simple configuration with high precision and at a low lost

A simple measurement method for micro volumetric flow rate with high precision and at a low cost is proposed for industrial use. A locally heated thermal flow is produced by small electric heater that is placed in the central part of an upwardly directed Poiseuille flow, and a thermocouple is located downstream of it. Furthermore, diffuser–reducer is set in a halfway position between the heater and the thermal sensor for enhancing the mixing of the locally heated fluid. It was found that the volumetric flow rate Qv in a pipe is directly proportional to the maximum diffusion temperature rise of the heated flow ΔTmax between the heater and the sensor. Qv can be obtained by using the linear relationship between ΔTmax and Qv. The linear relationship between ΔTmax and Qv was confirmed for water flow rate below 1 mL/min both experimentally and numerically. Furthermore, this flowmeter numerically confirmed that the change of water temperature at the pipe inlet could not affect the relationship between ΔTmax and Qv. Transient numerical simulations are performed using Storm/CFD2000 software. The unsteady three-dimensional Boussinesq set of equations was used in order to validate the measurement principle of this new micro flowmeter, and also to determine the optimized flowmeter design. Moreover, this flowmeter could be applied as a leak detector, because it is possible to measure the flow rate down to Qv=0 mL/min.