The microchannel has shown its superiority in many applications with high heat dissipations, such as high-performance CPU, solar cell, PEM fuel cells and laser diode arrays, etc. The microchannel heat sink can operate at a high heat flux because of its large surface to volume ratio. For the straight microchannel, the fluid mixing is poor and the heat transfer deteriorates as the boundary layer becomes thicken. The thermal performance of microchannel heat sink needs to be further improved to meet the demanding of high efficiency cooling for the new and innovative devices.  It has been proved that secondary flow exists as the working fluid flows in the wavy channel, which will contribute to the mixing of fluid and enhance the heat transfer process. Therefore, the wavy microchannel is an available option, which needs a small additional cost of pumping power and no fabrication of complex structures or coatings.

Silicon, aluminum and copper are the available materials used in heat sink manufacture, in which the copper has the superiorities, such as the highest thermal conductivity, good mechanical strength and easy machinability. The present copper microchannel fabrication technique (such as wire cut electrical discharge machining (EDM) or etching) usually has a smooth surface characteristic, which is not beneficial to the bubble nucleation and may need a large wall superheat to trigger the onset of nucleate boiling. The recent study showed that the ultrafast laser micromachining can fabricate microchannel with a rough surface and has merits of low time cost and high accuracy.

This study experimentally investigated the flow boiling of HFE-7100 in wavy copper microchannel heat sink (20mm×10mm), which was fabricated with the ultrafast laser micromachining approach, consisting of 20 wavy microchannels with triangular section (200μm×573μm). The experiment was conducted covered the mass fluxes of 43.43-217.12kg/(m^2^·s) and heat flux of 0-468.7kW/m^2^ at an inlet temperature of 33℃. Four flow patterns including bubbly flow, slug flow, churn flow and annular flow were captured with the visualization technique. Some confined bubbles have irregular shape with thinner liquid film were observed. In the low heat flux region, the dominant flow regime of heat transfer in the microchannels is the nucleation boiling and the heat transfer coefficient increases with the increase of heat flux. With the nucleation boiling suppressed gradually, the evaporation of thin liquid film begins to dominate and the heat transfer coefficient decreases with the increase of heat flux. The heat flux has a significant effect on heat transfer coefficient compared with the mass flux and vapor quality.


Experimental Study on Flow Boiling of HFE-7100 in Wavy Copper Microchannels

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

IMECE2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.