Simultaneous flow and thermal conductivity measurement of gases utilizing a calorimetric flow sensor

This contribution presents a calorimetric flow sensor that is capable of determining the thermal conductivity of gases (k) under flow conditions. The measuring principle relies on using high frequency heat generation at 200 Hz in order to confine the AC heat transfer into a thin region over the surface of the channel wall, where the flow velocity profile is always close to zero. The thermal conductivity of several common gases and their mixtures is measured for flow rates up to 750 sccm. The sensor takes advantage of DC excitation to measure the flow rate (Q) provided that the volumetric heat capacity (pc(p)) or the thermal diffusivity (alpha =k/(pc(p))) of the gas is known. This paper also presents two analytical models that qualitatively describe the measuring principles. Theoretically predicted functions fit well the experimental results.