Thermal boundary layers in critical flow venturis

Abstract We improve the usefulness of small (diameter  C T = 1 + K T Re − 1 / 2 Δ T / T 0 where Δ T is the difference between the CFV's inner wall temperature and the stagnation temperature. For CFVs made of stainless steel and copper with diameters of d = 0.56 mm, 1.1 mm, and 3.2 mm we measured K T ≈ −7 while theoretical predictions of K T by Geropp and Ding et al. are −1.7 and −3.845 respectively. Introducing the correction for room temperature changes ( C T ) measured in this work, reduces the room temperature sensitivity of the flow measured with the 0.56 mm diameter CFVs from 0.02 % K−1 to less than 0.003 % K−1. Smaller, but significant, improvements are achieved with larger CFVs.