The Investigation Of Porous Copper-powder Layer Prepared By Electroplating Technique And Its Enhanced Boiling Heat Transfer Performance

To improve boiling heat transfer efficiency,a functional structure with strengthening effect is created on the original surface.A porous structure in micro-scale has high specific surface area and boiling vaporization cores density,thereby becoming an important way to solve the thermal control problems in high heat flux phase.Generally,the porous structure is prepared by sintering,however,the high temperature and pressure in the fabrication process always weakens its bonding strength and structural stability,as well as destroys the intrinsic micro properties of the powder particles,which limit the further improvement of the boiling heat transfer performance of the sintered porous surface.Therefore,an electroplating bonding technology for porous copper-powder structure is proposed in this work.By using the electroplating layer as the bonding layer,the formation of porous structure at normal temperature was realized,and the intrinsic properties of copper powder particles were maintained.The morphology and bonding process of porous copperpowder structures were analyzed,as well as the fabrication parameters,such as current density,electroplating time,copper powder size and shape,were optimized by a scanning electron microscope(SEM).Moreover,the bonding strength and anti-disturbance ability of the electroplated porous surface were summarized accompanied by a thrust test and an ultrasonic vibration test,respectively.Along with water droplet spreading and down-absorption tests,the wettability of porous surface was discussed.The results show that with an optimum process parameters,it is feasible to electroplate copper powders onto a substrate securely and form an inter-connective porous layer with high stability and wettability.The boiling heat transfer performance of the porous structure prepared by copper powder electroplating was studied through the visual pool boiling heat transfer test.The results show that compared with the smooth surface,the porous copper-powder structure can increase the specific area,improve the gas storage capacity,enhance the wettabiliy,reduce the contact area between bubbles and porous structure,as well as reduce the activation energy required for the formation of vaporized cores.Therefore,in the boiling process,more bubbles in small size and short growth cycle can be formed on the porous copper-powder surface,leading to the greatly enhancement of the heat transfer efficiency.In addition,there was some significant difference of bubble dynamics between electroplated porous surface and smooth surface in the boiling experiment.In the low heat flux phase,the porous copper-powder structure can increase the number of vaporized cores,reduce the bubble size,shorten the bubble growth cycle and accelerate its detachment frequency,so that the surface can get into the nucleation stage in advance,and has an excellent boiling heat transfer performance.In the high heat flux phase,the porous copper-powder structure can maintain the stability of hydraulic pressure,delay the appearance of large bubbles,and make the surface still have a high boiling heat transfer efficiency.