Nucleate pool boiling of sintered coated porous surfaces with dielectric liquid, HFE-7200

The present study reports a substantial enhancement mechanism by optimizing the morphological parameters of sintered Cu/Ni alloy surfaces. An increase in the nucleation site densities of sintered surfaces by controlling the average surface roughness, porosity, particle diameter, and coating thickness yielded substantial augmentation in pool boiling of a highly wetting liquid. For instance, increasing the surface roughness of a sintered coated surface (sample B1) by 24.54 μm and reducing the particle diameter by 11.2 μm, porosity by 39%, coating thickness by 0.27, and pore radius by 0.31 mm resulted in an increase of more than 6.66x in heat transfer over the entire range of investigated heat fluxes. The other tested sintered surfaces (B2, B3, and B4) offered augmentations by 2.52x, 4.87x, and 2.17x, respectively. This substantial enhancement can be attributed to the large nucleation site densities. In addition, pool boiling testing for more than 80 hours showed no heat transfer performance degradation. To understand the performance and mechanisms underlying this substantial enhancement, the authors compared the surface morphology of these sintered surfaces with smooth polished, sandblasted, and sintered surfaces having different degrees of roughness under saturated nucleate pool boiling of a dielectric liquid (HFE-7200) through scanning electron microscopy. The use of sintering technology represents a potential approach to fabricating highly efficient and high heat flux boiling surfaces for dielectric and other highly wetting liquids.