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

The influence of gas transport properties on jet-impingement heat transfer is commonly represented through power-law Prandtl-number dependence, Nu ∞ Prn but experimental evidence for gas-to-gas sensitivity in strongly confined geometries remains limited. In present work, heat transfer from a single, fully confined impinging jet with single exit is investigated experimentally for five working gases (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-time-scale 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 downstream 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 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.