Novel post-processing methods for infrared measurements on porous surfaces

Abstract

Abstract Infrared (IR) thermography is a key diagnostic tool for non-invasive measurements of surface temperatures. However, for porous materials, particularly those employed in self-pumping transpiration cooling systems, conventional IR techniques suffer from significant inaccuracies due to local emissivity variations caused by multiple materials, surface roughness, and presence of liquid in the porous media. This study presents and compares three post-processing methods to enhance the accuracy of IR temperature measurements on saturated porous surfaces. A constant emissivity approach, a blackbody radiator method, and a novel differential method are applied to an Isopropanol filled porous sintered bronze plate under controlled experimental conditions. The results reveal that the conventional constant emissivity method leads to the largest errors and broadest temperature distributions. The blackbody radiator method improves accuracy by introducing a reference emissivity point but retains significant uncertainties. The differential method, leveraging a distribution of reference temperatures, achieves the highest precision, effectively resolving local emissivity variations and minimizing deviations from thermocouple reference measurements. This method enables a detailed spatial characterization of surface temperatures, particularly capturing the thermal gradients associated with evaporation in self-pumping cooling regimes. Furthermore, the effect of liquid in metallic porous samples could be demonstrated and shows clear differences to ordinary metallic surfaces such as the border of the porous sample. These findings provide a refined framework and experimental validation for accurate thermal diagnostics of porous surfaces under two-phase flow conditions.