The Effect Of The Micro/Nanostructure Surface On The Flow In The Microchannel

As a kind of small size high efficiency heat dissipation device,microchannel heat exchanger is widely used in the areas such as refrigeration,electric power,aerospace,waste heat recovery,fuel cells.In this thesis,the influence of the micro/nanostructure surface on the single phase flow in the microchannels were investigated by manufacture micro/nanostructure surface and building the experiment system.Micro/nanostructure surfaces were made with laser etching method,anodization and plasma treatment.By using the laser etching,linear micro groove structure surface was made on copper,aluminum and silicon and square shape groove structure was also made on copper.For the linear groove structure,shallow micro groove didn't change the surface roughness and contact angle.With the increase of the groove depth,the surface roughness increased and the contact angle decreased,which followed the Wenzel model.For the square shape groove structure,contact angle and surface roughness on the copper increased.The porous anode alumina was made via the anodization method.The contact angle of porous anode alumina is smaller than the contact angle on aluminum.After the plasma activation,the surface contact angle decreases,and after the plasma coating on the surface,it become superhydrophobic.A microchannels flow test system was build.The designed microchannels module could hold different micro/nanostructure surface substrate.The hydraulic diameter of semicircle microchannel and two rectangular microchannel were 30?m,282?m and 656?m respectively.The microchannels substrates were processed by laser etching.The surface roughness and contact angle of all the microchannels and substrate were measured.Through the matching experiments of different microchannels and different microgroove substrates,it is found that for microchannel with the same cross section,even if the roughness of different substrates are the same,the flow resistance of the microgroove structure substrates are larger than that of the flat substrates.For the different microgroove substrates within the same roughness,one with smaller etching distance has the larger pressure drop.The flow resistance on the substrate of the anodized aluminum film is smaller than that of the copper substrate.For rectangular microchannels of the same substrate,microchannels with smaller hydraulic diameters have larger flow resistance at the same Reynolds number.The copper visualization microchannels were designed and processed,and the visualization experiment was built to study the flow in the microchannels.The high-speed camera was used to observe the flow of the liquid plug in the microchannels,and obtained the dynamic contact angle and flow conditions at different flow rates.When the flow rate increases,the receding angle will gradually decrease;as the flow rate increases to a certain value,the liquid film formed by the retention can be observed behind the receding meniscus,and as the flow rate increases,the liquid film length will gradually increase.And there is a flow rate when the liquid film forming rate is the same as the liquid film breaking rate.Above the flow rate,the liquid film length fluctuates above and below the maximum value.