Study On Interface Enhanced Heat Transfer Based On Surface Modification And Liquid Metal Alloy

With the rapid development of the shipping industry,the modernization of ships has gradually improved,and marine automation and electrification technologies have been increasingly advanced.In particular,the development of electric propulsion ships has made some electronic components with high power and high heat flux density widely used in ocean vessels.This puts higher demands on the heat dissipation of marine electronic devices.Thermal contact resistance is one of the key factors that restrict the heat dissipation of electronic devices.Reducing the contact thermal resistance can effectively increase the efficiency of the thermal appliance,prolong the life of the electrical appliance,and ensure the safe of the electrical appliance.Thermal interface material is one of the biggest factors affecting the thermal contact resistance.Poor wettability of solid-liquid interface is one of the reasons for restricting the further application of high-performance gallium-based liquid metal alloy as thermal interface material.In this paper,gallium-based liquid metal is used as the thermal interface material,copper and aluminum are used as the substrate respectively.The method of improving the wettability of solid-liquid interface is explored.The thermal properties of the solid-liquid interface are measured.The thermal contact resistance of copper and aluminum substrates at different surface energies is predicted.In the copper substrate modified experiment,silver,nickel,molybdenum and tungsten were prepared by physical vapor deposition on a copper substrate,and then the liquid metal alloy was applied to the surface of samples to prepare sandwich structure samples.The thermal properties of the sample were measured using the laser flash method.The results show that the thermal contact resistance decreases with the increase of the surface energy of the surface material,and the thermal diffusivity and thermal conductivity increase respectively.Compared with the sandwich structure sample prepared by using the copper substrate,the contact thermal resistance of the sample deposited with the tungsten material was 64.05%lower than that of the sample prepared by the copper substrate,and the thermal conductivity was improved by 7.96%.Based on the surface modification experiment of copper substrate,this paper uses the prediction model to predict the thermal contact resistance of the copper substrate filled with different surface energy by using the gallium-based liquid metal alloy as the thermal interface material,and further explores the effect of controlling the mechanism of how wettability effect the thermal contact resistance.In the experiment of surface modification of aluminum substrate,a uniform thin aluminum oxide layer was prepared on the surface of the aluminum substrate by anodic oxidation of chromic acid.In this experiment,TG-250 and gallium-based liquid metal alloy were used as thermal interface materials respectively,and the thermal properties of samples were measured by the laser flash method.The results show that the application of gallium-based liquid metal on the surface of aluminum substrate is an effective method to reduce the thermal contact resistance.The thermal contact resistance of the sample using gallium-based liquid metal alloy as the thermal interface material under the pressure of 0.05MPa is 3.575mm2K/W,the contact thermal resistance was reduced by 99.67%compared with the sample with TG-250 as the thermal interface material under the same pressure.When the pressure is less than 0.3MPa,the contact thermal resistance gradually decreases with the pressure increases;when the pressure is larger than 0.3MPa,the contact thermal resistance does not substantially change with the change of the pressure.In the experiment of electrowetting to enhance the wettability of liquid metal alloy and aluminum substrates,the wettability between liquid metal alloy and metal substrate was measured in air,nitrogen and silicone oil environments respectively.The results showed that liquid metal alloy in air and nitrogen is easily oxidized,and the breakdown voltage of electrowetting is about 40V,and the maximum contact angle is 140°and 136.8°,respectively.In the silicone oil environment,the contact angle changes obviously,and the minimum value can reach 118°.Using the prediction model to measure the contact angle change in the silicone oil environment,it is predicted that the contact thermal resistance of the sample prepared under the maximum voltage of the electrowetting of the silicone oil environment should be able to reduced by more than 40%.From the above work,the paper draws the following conclusions:(1)The surface wettability can be effectively controlled by surface coating.The surface energy of the surface deposited with tungsten material is the highest,and the sample has the best thermal conductivity.(2)The improvement of the wettability of the solid-liquid interface can effectively reduce the separation distance of the solid-liquid interface.The oxidation of liquid metal is the cause of the error between the prediction model and the experimental measurement.(3)The oxide film formed on the surface of the aluminum substrate by chromic acid anodization can effectively block the direct contact between the gallium-based liquid metal and the aluminum substrate.When the gallium-based liquid metal is used as the thermal interface material on the aluminum substrate,the interface heat transfer effect is far.Better than thermal grease.(4)Dielectric wetting can regulate the wettability of gallium-based liquid metal on the surface of aluminum substrate,and it has the best effect in silicone oil environment.It is predicted that the wettability of liquid metal and aluminum substrate surface can be improved by using electrowetting.Reduce contact thermal resistance by more than 40%.