Parallel Channel Instability, Critical Heat Flux and Impact of Inlet Restriction in Short Narrow Multi-Microchannel Heat Sink

M. R. Kærn*, G. Criscuolo, K. E. Meyer, W. B. Markussen

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingArticle in proceedingsResearchpeer-review

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Abstract

The current experimental work focusses on the parallel channel instability and possible premature critical heat flux in a short, narrow multi-microchannel heat sink with and without individual channel inlet restrictions. The application was cooling of power electronics and the target footprint area was (10 x 10) mm2. The heat sink was fabricated in copper by micro-milling and had 25 rectangular channels (198 μm wide, 1167 μm high). The heat sink featured customized exchangeable PEEK inserts, which constituted the inlet and outlet plenums as well as featuring the individual channel inlet restrictions, which had a 40 % area contraction compared with the channel area. Refrigerant R134a was adopted as the working fluid and the critical heat flux was measured at several different mass fluxes and different inlet subcooling at around 31 °C saturation temperature with and without inlet restriction. High-speed visualization was used to study the flow patterns and two-phase instability. The visualizations showed that the inlet restrictions stabilized the flow with respect to the parallel channel instability that was otherwise present at lower mass fluxes, thus avoiding vapour backflow into the inlet plenum. At higher mass fluxes, the visualizations did not indicate significant vapour backflow with or without individual channel inlet restrictions. Fourier analysis was used to study the instability at
the lowest mass flux (339 kg/m2s) at a subcooling of 5.2 K without inlet restriction. Here the main frequency of the twophase oscillations was very fast (14􀀚􀀑􀀘 Hz) and systematic. The absolute pressure sensors captured twice this frequency: This is in good agreement since these sensors captured the vapour backflow from both ends of the channel row. The current high frequency two-phase oscillations led to a marginally lower critical heat flux (2-9 %) without use of the individual channel inlet restrictions.
Original languageEnglish
Title of host publicationProceedings - 15th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics
PublisherAmerican Society of Thermal and Fluids Engineers
Publication date2021
Pages1770-2339
Publication statusPublished - 2021
Event15th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT 21) - Virtual conference
Duration: 25 Jul 202128 Jul 2021

Conference

Conference15th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT 21)
LocationVirtual conference
Period25/07/202128/07/2021

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