Devices used for various electronic purposes are increasing in power consumption and performance. Due to this growth, the amount of heat dissipated over a small surface area has proportionally continued to increase. Despite previous efforts involving single phase natural and forced convection, these methods are no longer effective in high heat removal. Research in two-phase liquid cooling has become more prominent. Boiling has the potential to yield large critical heat flux values, high heat transfer coefficients and lower pressure drops. Many different surface enhancements and working fluids have been tested to increase efficiency and minimize heat losses.

Flow boiling in microchannels have been widely explored in literature for high heat flux dissipation. Microchannels are compact and subsequently easy to manufacture. However, due to flow instabilities that accompany microchannels, different configurations and additional modifications have been explored in order to maximize performance. In this work, a radial geometry is experimentally investigated with a flow inlet over the center of the chip. This central inlet creates a reduction in flow length and therefore a reduction in pressure drop and flow instabilities. Two testing surfaces were explored including a radial microchannel array and a radial offset strip fin array. To maximize performance even further, a gap has been added between the cover plate and testing surface to increase flow area and reduce pressure drop. One significant observation shows that an increase in flow rate mitigates the instabilities seen in the channels and prolongs critical heat flux (CHF). Due to these phenomena, all configurations are tested in the modified configuration with higher flow rates ranging from 120-320 mL/min.

Radial microchannels with an added gap yielded maximum performance values of 385.5 W/cm^2 at 42.7°C wall superheat with a high pressure drop of about 140 kPa while the offset strip fin configuration achieved much higher heat transfer performance with CHF values exceeding 900 W/cm^2 at 58.6°C wall superheat. The offset strip fin geometry shows significant performance enhancements compared to the microchannels. For both the gap geometries and the closed geometries, the offset values are much higher than the radial microchannels.

Library of Congress Subject Headings

Heat--Transmission; Ebullition; Fluid-structure interaction; Microfluidics; Heat exchangers--Fluid dynamics

Publication Date


Document Type


Student Type


Degree Name

Mechanical Engineering (MS)

Department, Program, or Center

Mechanical Engineering (KGCOE)


Satish G. Kandlikar

Advisor/Committee Member

Risa Robinson

Advisor/Committee Member

Alfonso Fuentes-Aznar


Physical copy available from RIT's Wallace Library at QC320 .R43 2016


RIT – Main Campus

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