Enhanced two-phase cooling using bi-particle-size sintered particle evaporator with distributed liquid supply capillary wicks
Egbo, Munonyedi Kelvin
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Liquid-vapor, phase-change heat transfer using wicks can provide reliable and high heat flux cooling capability, especially in microgravity applications. However, the maximum heat removal capacity, also known as Critical Heat Flux (CHF), is related to the capillary-driven liquid supply limit and/or vapor removal limit. A key was to develop a novel wick structure, offering efficient liquid supply as well as vapor removal pathways. First, a Bare Surface Evaporator with Phase-Separating Wick (BEPSW) was examined to fundamentally understand the liquid supply and vapor removal limits in a downward facing orientation for microgravity environment. The BEPSW was made of a bare surface evaporator for the efficient evaporation, a distributed liquid supply channels, and a phase-separating wick for enhanced liquid supply and vapor removal. The bare surface was fabricated using a copper disk 19.1 mm in diameter, while the post and phase-separating wicks were manufactured using 10 and 3 layers of sintered copper particles, respectively. Experimental results showed that the distributed liquid supply channels effectively supplied liquid to the heated surface, thus enhancing CHF and HTC. The results also showed that the CHF increases as the pitch distance decreases from Lp = 7 to 3.5 mm in both particle sizes due to the increased liquid supply through the post wicks, while it decreases below Lp = 2.5 mm in both particle sizes due to the liquid entrainment limit, i.e., the maximum CHF is observed at Lp = 2.5 to 3.5 mm, for the average particle sizes <dp> = 350 and 550 μm. Moreover, the CHF increases as the particle size increases due to the increased permeability. To further enhance CHF and HTC, the capillary performance of bi-particle sintered copper wick was investigated, and the result showed that the bi-particle size wicks enhanced capillary performance, by 27 to 35%, relative to the uniform particle wicks. Finally, the CHF and HTC were further enhanced using the bi-particle size sintered-particle evaporator wicks compared to the BEPSW, since it increased capillary pressure.
Thesis (Ph.D.)-- Wichita State University, College of Engineering, Department of Mechanical Engineering