Submerged jet impingement cooling using nanostructured plates

Official URL: http://dx.doi.org/10.1016/j.ijheatmasstransfer.2012.12.039

In this paper, the results of a series of heat transfer experiments conducted on a compact electronics cooling device based on single phase jet impingement technique are reported. Deionized-water is propelled into four microchannels of inner diameter 584µm, which are used as nozzles and located at a nozzle to surface distance of 1.5mm. The generated jet impingement is targeted through these channels towards the surface of two nanostructured plates with different surface morphologies placed inside a liquid pool filled with deionized-water. The size of these nanostructured plates are 35mm x 30mm and they consist of copper nanorods grown on top of a silicon wafer substrate of thickness 350 µm coated with a 50 nm thick copper thin film layer (i.e. Cu-nanorod/Cu-film/Silicon-wafer). Nanorods were grown using a sputter glancing angle deposition (GLAD) technique. First type of nanostructured plates comprises of ~600 nm long vertically aligned copper nanorod arrays grown with nanorod diameters and spacing varying between ~50-100 and 20-100 nm, respectively. The second type consists of ~600 nm long tilted copper nanorod arrays grown with diameter values varying between ~50-100 nm and spacing in the range of 20-50 nm. Heat removal characteristics induced through jet impingement are investigated using the nanostructured plates and compared to the results obtained from a plain surface plate of copper thin film coated on silicon wafer surface. Volumetric flow rate and heat flux values are varied between 107.5-181.5 ml/min and 10000-57143 W/m2, respectively, in order to better characterize the potential enhancement in heat transfer by nanostructured surfaces. Significant heat transfer enhancement using the nanostructured plate utilizing vertical nanorods has been obtained compared to flat plate. This enhancement is attributed to the increased heat transfer surface area and the single crystal property of the vertical Cu nanorods. On the other hand, nanostructured plate with tilted nanorods has been found to show poorer heat transfer performance compared to both the nanostructured plate with vertical nanorods and plain surface plate in the experiments performed. The lower heat transfer rate of the tilted Cu nanorods is believed to be due to the decreased supply of liquid jets to the base of the plate caused by their closely spaced dense array structure. In addition, non-single crystal structure of the tilted nanorods and resulting enhanced surface oxidation could further decrease their heat transfer performance.