Abstract

As technology advances due to continuous research, devices are becoming more compact, efficient, and powerful. Therefore, heat rejection from such devices becomes ever so critical to maximizing their potential. Compared to other heat extraction methods, boiling provides one of the highest heat transfer coefficients. The heat extraction due to the boiling process is limited to the Critical Heat Flux (CHF). At CHF, an insulating layer of escaping bubbles forms upon the surface to prevent boiling continuity. Subsequently, the surface temperature increases uncontrollably, leading to a system failure. Hence, the elevation of CHF is critical to boiling enhancement. Improvements to the heat transfer process can be made with either surface manipulation or liquid manipulation. Based on previous studies, it is found that the removal of bubbles from the heater surface is critical to enhancing performance. Therefore, it is hypothesized that if a bubble can be encouraged to reach liquid-gas the interface quickly, gains in the boiling performance can be achieved. Due to the vapor bubble's movement in liquid bulk, it becomes critical to understand the influence of liquid height on pool boiling for enhancement. While pool boiling enhancement using heating surface modification is extensively studied and documented, there is a research gap between understanding the effect of liquid height at high heat fluxes. Thus, this study tries to evaluate the influence of liquid height on pool boiling performance at higher heat fluxes and identify the underlying bubble movement mechanism. It is observed that as CHF increases with liquid height. Moreover, it is observed that bubble movement is more effortless at low liquid height resulting in higher HTC. On the other hand, larger liquid height provides improved rewetting of the surface resulting in higher CHF. Upon analysis of high-speed recording of the escaping bubbles, it was observed that the maximum heat transfer coefficient is observed when the liquid height is about four times the height of the departing bubble diameter.

Library of Congress Subject Headings

Heat--Transmission; Ebullition; Fluid mechanics; Fluid dynamics

Publication Date

12-2020

Document Type

Thesis

Student Type

Graduate

Degree Name

Mechanical Engineering (MS)

Department, Program, or Center

Mechanical Engineering (KGCOE)

Advisor

Satish Kandlikar

Advisor/Committee Member

Jason Kolodziej

Advisor/Committee Member

Robert Stevens

Campus

RIT – Main Campus

Plan Codes

MECE-MS

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