An experimental method to quantify local air-side heat transfer coefficient through mass transfer measurements utilizing color change coatings

This paper presents a visualization method to quantify local air-side heat transfer coefficient (HTC). It is challenging to measure local air-side HTC with good accuracy, especially for complicated geometries and real heat exchangers. The present method relies on measuring convective mass transfer and applying the analogy between heat and mass transfer. It is based on the chemical interaction between a pair of coating material and tracer gas. The coating material absorbs tracer gas and changes its color. Therefore, a visualization procedure is developed to correlate color change on the surface to the local mass transfer coefficient. In this research, the coating formulation, coating methods, and surface topography are evaluated to make sure the analogy between heat and mass transfer is valid. The experimental results of the flat plate in laminar flow show that the standard uncertainty of the local heat transfer coefficient is 15%. Furthermore, the results also show good agreement compared with the analytical Blasius solution except in the vicinity of the leading and trailing edges. Because of these promising results, it seems feasible to use this method to acquire local air-side HTC through a visualization approach for more complicated geometries.