Chinmay Patil

Abstract

The continuous development of high performance chips and growing miniaturization trend in the electronics and microelectronics industry requires efficient systems removing large amount of heat over a small footprint. It has been experimentally proven that pool boiling has the ability to remove large heat fluxes by maintaining a small value of wall superheat. This heat transfer performance can be further augmented with the use of enhanced surfaces. The present research is focused on developing microporous surface coatings on the plain and microchannel surfaces to further enhance pool boiling heat transfer.

In this work, a two-step electrodeposition technique involving application of high current densities for a short time, followed by a lower current density for a longer time was investigated. This technique was developed to control the pore size and porous layer thickness on copper substrate. Detailed analysis of the electrodeposition process was conducted, and parameters for creating different morphologies for of enhanced surfaces were obtained. Variety of morphologies were prepared and tested for pool boiling heat transfer performance. Cauliflower like morphology yielded maximum critical heat flux (CHF) of 1,490 kW/m2 with degassed water boiling giving maximum heat transfer coefficient of 179 kW/m2°C.

The study was further expanded to microchannel surfaces. The optimal electrodeposition parameters were employed to selectively coat the fin tops of open microchannel structures. Effects of geometrical parameters of the microchannels were investigated on pool boiling performance at atmospheric pressure. A maximum value of critical heat flux of 3,250 kW/m2 was obtained for Chip 9 (fin width = 200 μm, channel width = 500 μm and channel depth = 400 μm) at a wall superheat of 7.3 °C. A record value of heat transfer coefficient of 995 kW/m2°C was achieved for Chip 12 with a different channel width of 762 μm and a heat flux of 2,480 kW/m2 at a wall superheat of 2.5 °C.

High speed images of the boiling process were obtained and the bubble dynamics and heat transfer mechanism were studied. The bubble growth and heat transfer processes are altered when the boiling takes place preferentially on the fin tops only. The visual studies indicate a microconvective mechanism in which bubbles leaving from the fin tops induce a liquid circulation in the microchannels. A theoretical model of the heat transfer and bubble dynamics was proposed. The model is not a predictive model, but gives a general idea of the heat transfer process.

Library of Congress Subject Headings

Heat sinks (Electronics); Heat exchangers--Fluid dynamics; Ebullition; Microfluidics

Publication Date

4-22-2014

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

Denis Cormier

Advisor/Committee Member

Mario Gomes

Comments

Physical copy available from RIT's Wallace Library at TP363 .P38 2014

Campus

RIT – Main Campus

Plan Codes

MECE-MS

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