Abstract

In industry, boiling heat transfer is extensively used to efficiently dissipate high heat fluxes from heated substrates. Such industrial applications of boiling include cooling of reactor cores in nuclear power plants, steam generation in industrial boilers, and cooling of high heat flux generating electronic equipment. The maximum heat flux dissipated during boiling is limited by critical heat flux (CHF). At CHF, due to very high bubble generation and coalescence rates, a stable insulating vapor film is formed on the heated surface that leads to very high surface temperatures in a short time. The sudden temperature overshoot causes thermal breakdown, and therefore CHF is disastrous in all industrial applications. Owing to limited visualization of the boiling surfaces and dependence on temperature monitoring only, boiling systems are run at relatively low heat fluxes, ~50% of CHF limit due to safety considerations. The study presented here is focused on developing a method for identifying and analyzing acoustic signatures in the nucleate boiling regimes and using acoustic mapping as a monitoring tool to detect impending CHF. Initially, the sound waves generated through bubble coalescence and bubble collapse during boiling are captured for the plain copper chip. It is observed that the boiling sound is dominant in the frequency range of 400-500 Hz, while additional amplitude peaks in the frequency range of 100-200 Hz are also observed at higher heat fluxes (>100 W/cm²). Further, it is observed that just before CHF, there is a sudden drop in amplitude in the frequency range of 400-500 Hz. A similar study was performed on two additional microporous surfaces and similar acoustic trends as that of the plain copper chip was observed for both the chips. Coupling these observations with high speed visualization, the study indicates that a continuous acoustic mapping during boiling can be used as a tool to predict the impending CHF in boiling systems.

Publication Date

11-9-2019

Document Type

Thesis

Student Type

Graduate

Degree Name

Mechanical Engineering (MS)

Department, Program, or Center

Mechanical Engineering (KGCOE)

Advisor

Satish G. Kandlikar

Advisor/Committee Member

Mario Gomes

Advisor/Committee Member

Rui Liu

Campus

RIT – Main Campus

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