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Journal of Flow Visualization and Image Processing
SJR: 0.161 SNIP: 0.312 CiteScore™: 0.5

ISSN Print: 1065-3090
ISSN Online: 1940-4336

Journal of Flow Visualization and Image Processing

DOI: 10.1615/JFlowVisImageProc.2017020783
pages 117-136

VISUALIZATION STUDY OF VAPOR FORMATION DURING POOL BOILING UNDER MODIFIED CONFINEMENT SURFACES

Jason K. Ostanek
Purdue University, West Lafayette, IN 47906, USA

ABSTRACT

Understanding and predicting the effects of confinement on pool boiling is important for increasing the power density of electronic systems using two-phase, thermosyphon cooling systems. In comparison with spherical bubble formation in unconfined pool boiling, the presence of a confining surface near the heated surface will result in the formation of deformed/elongated bubbles. The present visualization study investigates the effects of confinement through high resolution, still photography taken from underneath a transparent heater test surface. The heater was comprised of an ITO-coated, glass substrate. Saturated pool boiling experiments using a dielectric refrigerant, RE347mcc (HFE-7000), were performed at atmospheric pressure for a flat, upward-facing surface. Unconfined tests were performed as a baseline, and three confining surfaces were tested: a plain surface, a surface with a rib, and a surface with relief holes drilled in it. The visualization study shows details of vapor structures growing underneath the confinement surfaces and escaping around the edges of the confinement surfaces. As the vapor escapes the confining surface, incoming liquid is drawn in to replenish the heater. The incoming liquid would occasionally displace any pre-existing vapor pockets, resulting in finger-like structures forming within vapor pockets. In some cases, a growing vapor pocket would initiate during the liquid replenishment, adjacent to existing vapor pockets. The newly formed and expanding vapor pocket was found to displace the surrounding liquid and the pre-existing vapor pockets. As heat flux is increased, the size and shape of the large vapor structure changes as well as the wetted area between the structures. For the plain surface, a vapor layer was observed on the test surface at a heat flux of 5 W/cm2 while the rib and drilled surfaces remained wetted.


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