Thermal performance evaluation of advanced multistage heat sinks in experimental pool boiling study

Two identical novel multistage cross-flow porous structures, referred to as MCPS 1 and MCPS 2, were tested in a controlled experimental pool boiling setup using FC-72 dielectric fluid under atmospheric conditions. The test samples were identical in terms of footprint area and channel height. Both featured cross-flow channels and circular pores, with pore diameters of 0.325 mm and 0.4 mm and channel widths of 1 mm and 1.5 mm, respectively. Tests were conducted in three distinct orientations. The vertical configuration, in which the lower-stage channels were aligned parallel to the buoyancy force, was identified as the optimal orientation for both samples. In this configuration, maximum heat fluxes of 107 W/cm² and 109 W/cm² were achieved using MCPS 1 and MCPS 2, respectively, at relatively lower wall superheats of 42 °C and 43 °C. The highest heat transfer coefficients were 47,563 W/m² K for MCPS 1 and 39,132 W/m² K for MCPS 2. High-speed imaging of MCPS 2 revealed a larger bubble departure diameter and a lower bubble frequency compared to MCPS 1, which hindered the replenishment of fresh liquid and consequently led to a decline in the heat transfer coefficient.