Transforming pool boiling into a pumpless self-sustained flow boiling system for efficient cooling at high heat fluxes

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Current trend of electronics miniaturization introduces higher heat generation rates while substantially reducing surface area for heat dissipation. Phase change cooling with pool boiling is an attractive cooling method. Flow boiling is more efficient but requires a pump, which makes it more complex. This project presents an innovative concept that transforms pool boiling into a self-sustained pumpless flow boiling system and dramatically improves cooling performance. It utilizes a tapered gap in which a bubble expands in a preferential direction of increasing flow area and creates a self-sustained flow over the heater surface. The proposed work will provide thorough understanding of the underlying physics and enable optimal designs with different fluids for dramatically improving heat dissipation. It will offer educational opportunities to undergraduate and graduate students, while creating a new outreach activity "TinkerEngLab" with hands-on experience to minority and women students. The team will participate in an outreach activity called Beyond 9.8 for middle school students from underprivileged schools.The goal of the project is to develop a fundamental understanding of the fluid flow and heat transfer mechanisms that drive the self-sustained flow as a bubble grows and expands in a tapered gap. It will be accomplished through – 1) analytical work to establish the link between heat transfer around a growing bubble, pressure recovery and pressure drop in the tapered microgap, 2) numerical work to provide insight into bubble growth and instantaneous pressure field, and 3) experimental work for validation and practical data. Fundamental information on microlayer formation under a bubble and pressure distribution at the wall at various stages of bubble growth will be obtained. The numerical simulation of squeezing bubble will utilize advanced code developed in the lab to predict pressure field in the tapered microgap under dynamic conditions, and these will be experimentally validated by pressure mapping using micro-electromechanical sensors and high-speed visualization. The findings from the numerical study will be incorporated in developing a theoretical bubble squeezing model for flow dynamics and heat transfer. The knowledge and the model will provide design theories for developing highly efficient cooling systems with different fluids under different operating conditions. The work is expected to introduce a paradigm shift as pool boiling will no longer be limited by a stagnant pool of liquid, but will incorporate flow for achieving unprecedented cooling performance without requiring a pump. Its main application includes electronics cooling, but the work will open up new avenues in industrial and commercial applications as well.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.