Experimental Validation of Reynolds–Prandtl Scaling for Confined Gas Jet Impingement Heat Transfer

Abstract

Abstract. The influence of gas transport properties on jet impingement heat transfer is commonly represented through a power law Prandtl number dependence, Nu∝Prn, but experimental evidence for gas-to-gas sensitivity in strongly confined geometries remains limited. In the present work, heat transfer from a single, fully confined impinging jet with a single exit is investigated experimentally for five working gases (dry air, N2, Ar, CO2, and He) at matched jet Reynolds numbers, ReD≈15,000–30,000, and a fixed jet-to-target spacing of H/D=1. Spatially resolved heat transfer coefficients are obtained using transient liquid crystal thermography coupled with a one-dimensional transient conduction model based on Duhamel superposition. The driving temperature of the heat transfer experiment at the impingement surface is reconstructed from thermocouple measurements using a two-timescale step model with thermocouple response correction, ensuring consistent thermal boundary conditions across gases. After Reynolds normalization, air, N2, Ar, and CO2 show similar normalized heat transfer distributions, and a common Prandtl scaling collapses the stagnation and wall-jet regions. Helium remains an outlier despite Reynolds–Prandtl normalization, with a more compact footprint and steeper radial decay. A Brinkman number analysis indicates increased sensitivity of Helium to viscous dissipation and recovery temperature effects, due to the higher jet velocities required for Reynolds matching; a Brinkman-based rescaling improves the collapse. Overall, the results show that modest gas property variations can measurably alter confined-impingement heat transfer distributions, and that Reynolds–Prandtl scaling alone is insufficient for low-density gases under matched Reynolds conditions.