Quantitative Evaluation of the Dependence of Pool Boiling Heat Transfer Enhancement on Sintered Particle Coating Characteristics

Abstract

Immersion cooling strategies often employ surface enhancements to improve the pool boiling heat transfer performance. Sintered particle/powder coatings have been commonly used on smooth surfaces to reduce the wall superheat and increase the critical heat flux (CHF). However, there is no unified understanding of the role of coating characteristics on pool boiling heat transfer enhancement. The morphology and size of the particles affect the pore geometry, permeability, thermal conductivity, and other characteristics of the sintered coating. In turn, these characteristics impact the heat transfer coefficient and CHF during boiling. In this study, pool boiling of FC-72 is experimentally investigated using copper surfaces coated with a layer of sintered copper particles of irregular and spherical morphologies for a range of porosities (∼40–80%). Particles of the same effective diameter (90–106 μm) are sintered to yield identical coating thicknesses (∼4 particle diameters). The porous structure formed by sintering is characterized using microcomputed tomography (μ-CT) scanning to study the geometric and effective thermophysical properties of the coatings. The boiling performance of the porous coatings is analyzed. Coating characteristics that influence the boiling heat transfer coefficient and CHF are identified and their relative strength of dependence analyzed using regression analysis. Irregular particles yield higher heat transfer coefficients compared to spherical particles at similar porosity. The coating porosity, pore diameter, unit necking area, unit interfacial area, effective thermal conductivity, and effective permeability are observed to be the most critical coating properties affecting the boiling heat transfer coefficient and CHF.

Liquid-Vapor Phase-Change Heat Transfer on Functionalized Nanowired Surfaces and Beyond

“…24,80,81 As such, a lot of efforts have been devoted to enhancing nucleate boiling heat transfer efficiency (before the CHF) and delaying the occurrence of boiling crisis, i.e., increasing CHF, through manipulating bubble behaviors using micro/nanostructures. 6,58,60,[82][83][84][85][86][87][88][89][90][91][92][93][94] Compared with the plain surface, micro/ nanostructured surfaces can decrease the ONB, improve the HTC, and increase the CHF in nucleate boiling heat transfer regime (Figure 2A). [61][62][63]82,[95][96][97][98][99][100] The underlying mechanisms for the enhancements have been attributed to the increased nucleation site density for efficient liquid vaporization, increased solid-liquid interface for sufficient heat transfer area, and enhanced capillary pumping for rapid liquid supply.…”

Area-scalable high-heat-flux dissipation at low thermal resistance using a capillary-fed two-layer evaporator wick

“…The effect of particle size in sintered coatings on pool boiling behavior has been extensively studied in the literature [19,20]. In addition, there have been detailed characterizations and statistical descriptions of sintered wick structures [21], and their effects on pool boiling [22]. However, few studies have addressed the effect of particle size during capillary-fed boiling; moreover, the wick types, heating area, and wick thicknesses differ between each of these studies.…”

Role of nanoscale roughness in the heat transfer characteristics of thin film evaporation

“…Experimental studies have shown that nanoscale surface roughness affects the meniscus profile and heat transfer rate in thin film evaporation [6]. For larger structures, e.g., hoodoo structures [7], micropillars [8], sintered mesh [9], sintered microparticles [10], and hierarchical structures [11], local roughness at the contact line also plays a role in determining heat transfer rate. In order to design surface structures that provide further heat transfer enhancement, it is of fundamental significance to understand the heat transfer characteristics of the evaporating meniscus on rough surfaces.…”