Development of a Thermal Based Flow Measurement Technique for Very Low Flow Velocities

Abstract

A measurement technique for very low flow velocities based on thermal measurements is proposed as an alternative for measurements in larger- diameter pipes. The velocity of a locally accelerated thermal flow is calculated from the time shift between registration of heat pulse and distance separating the two temperature sensors. Additional study using PIV and high-speed recording in analysing and quantifying the flow pattern induced by heat pulses in static and dynamic environments is performed.

The results from this study showed that a clear and distinct registration of heat pulses was necessary in order to easily calculate the average velocity. Based on small-scale laboratory works, location of the measurement equipment was decisive in terms of getting best possible registrations of heat pulses. The results show a jet-like pattern of the movement induced by heat pulse in static environment and the collision of jets resulting in a mushroom-like vortex structure in the dynamic environment.