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COBEM 2021
26th International Congress of Mechanical Engineering
THERMAL AND HYDRODYNAMIC BEHAVIOR OF A MICRO-FINNED HEATSINK FOR CONVECTIVE FLOW BOILING OF DIELECTRIC FLUID
Submission Author:
Jessica Martha Nunes , SP
Co-Authors:
Jessica Martha Nunes, Willy Kelton Nobrega Azevedo, Elaine Maria Cardoso
Presenter: Jessica Martha Nunes
doi://10.26678/ABCM.COBEM2021.COB2021-0695
Abstract
It´s notable the advancement in the high-power electronics development, applicable to the most diverse industrial segments, as well as the miniaturization of such devices, requiring higher levels of energy dissipation in high-performance electronic components. The scientific community has been working on the development and optimization of compact heat exchangers, based on convective boiling associated with dielectric fluids, where it is possible to obtain high heat transfer rates. This work aims to experimentally evaluate the thermal and hydrodynamic behavior of a micro-finned heatsink, using convective flow boiling of the HFE-7100. Square micro-pin fins (with 300 μm wide and 250 μm spacing) were manufactured on a copper surface, through a micro-milling process, with two micro-pin fin heights (160 and 300 μm) aligned to the fluid flow direction. The pressure drop and surface temperature behavior were analyzed for different mass fluxes (800, 1000 and 1200 kg/m²s) and inlet subcooling (10 and 20 °C). An increase in the subcooling shifts the boiling curve to the left; the higher the inlet subcooling the larger the portion of the micro heatsink in the biphasic region and, consequently, the higher the maximum heat flux characterized by an inflection of the boiling curve. The effect of mass flux on the boiling curve and heat transfer coefficient (HTC) is negligible for the inlet subcooling of 10 ºC; in the case of 20 °C, an increase in mass flux causes an enhancement in the HTC for low to moderate heat flux; by increasing heat flux, the HTC is no longer influenced by the mass flux, showing the gradual control of boiling over convection as the main heat transfer mechanism. For the single-phase flow region, the pressure drop is similar regardless of the inlet subcooling. However, in the two-phase flow region, the pressure drop increases exponentially with the heat flux as the rate of vapor generation becomes pronounced. Besides, decreasing the inlet subcooling increases the pressure drop, at the same heat flux (the lowest inlet subcooling results in a higher vapor quality along the microchannels, leading to a larger pressure drop). The visualizations indicated that isolated bubbles formed between the adjacent fins and they move mainly between the fins, parallel to the flow direction. For high heat fluxes and low subcooling, the vapor core fills the entire length of the heatsink; the annular flow regime becomes prominent and reverse flow may occur, causing some instabilities which increase the pressure drop.
Keywords
Two-phase Flow, Convective Heat Transfer, pressure drop, micro-pin fin, HFE-7100
