The continuous growth and demand of increased operating performances of electronics has brought about an increase in the chip power density posing threat to the thermal management of these devices. Although numerous thermal solutions ranging from passive to active cooling together with a variety of working fluids have been adopted, however, the question whether these available cooling methods could meet up with the ever-growing need for increased operating performances is a concerning one. Jet impingement cooling has been effectively used in many industrial applications due to its high heat transfer capability. The limited study at the micro scale suggests that it exhibits excellent heat transfer performance relative to conventional parallel flow in microchannels. Recently, Carbon dioxide in its supercritical state (304 K and 7.3 MPa) has been proven to be an excellent working fluid in dissipating high heat fluxes. Owing to the properties of this fluid (sCO2) and its high specific heat near the pseudocritical point, the heat transfer rate can be enhanced significantly compared traditional working fluids. However, knowledge about the heat transfer characteristics of micro jet impingement with Carbon dioxide in this state are lacking. In addition, flow boiling has been recognized to significantly enhance heat transfer rate due to its large thermal capacity giving an opportunity to further enhance the cooling ability of Carbon dioxide. In line of this continuous innovation the flow and the heat transfer characteristic of micro jet impingement with CO2 in both single-phase and two-phase were experimentally studied. A micro fluidic device was manufactured leveraging MEMS techniques. The micro device included a circular serpentine heater of diameter 2.01 mm and three resistance temperature detectors (RTDs) sputtered on a glass substrate made of fused silica, providing heating and temperature measurements, respectively. The heater, RTDs and their vias were sputtered with the calculated lengths, widths and thicknesses to achieve the desired resistances. The RTDs were arranged on the heater in a concentric manner to measure the average radial temperature distribution as the flow was assumed to be symmetric. The effects of the working fluid was investigated under governing parameters such as radial position, heat flux, mass flow rate, inlet temperature and inlet pressure. Results from the single-phase investigation showed a higher sensitivity of the heat transfer rate to the proximity to the pseudocritical temperature of the fluid with the optimum heat transfer rate recorded around the pseudocritical temperature subject to the increased specific heat around this region. By utilizing the flow boiling process, a further enhancement was observed pre the critical heat flux condition, suggesting a need to operating within the nucleate boiling region in its industrial adoption. It was recorded that the single jet performed better than the multi jet as a result of the interjet spacing which governs the effect of the colliding jets. Finally, several correlations with minimal mean absolute errors were introduced due to discrepancies from literatures.
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Doctor of Philosophy (Ph.D.)
College of Engineering and Computer Science
Mechanical and Aerospace Engineering
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Adeoye, Stephen, "Heat Transfer Characterization of Carbon Dioxide in Micro Impinging Jet(s) Near Critical Conditions" (2022). Electronic Theses and Dissertations, 2020-. 1167.