The Research On Heat Transfer Mechanism Of Metal-Plastic Composite Microstructure Heat Radiator

With the high-speed development of micro electromechanical system (MEMS) as well as areas such as biomedical technology, aerospace, the complex multi-function systems have produced more and more heat. Ordinary heat radiator could not meet the increasing heat flux. At the same time, because the thermal environment is more and more harsh and volume is smaller and smaller, in order to solve the problem of cooling, higher and higher technical requirements including miniaturization of the heat radiator are put forward.At present, the methods to solve the problem of high efficient heat dissipation mainly include three points.The first method is to increase the specific surface area. The second method is to modify the material in order to increase the thermal conductivity and radiation emissivity. The third way is to increase surface convective heat transfer coefficient.The common microstructure heat radiator is mainly composed of aluminum, copper and other materials which have high thermal conductivity. Considering from the angle of material properties and processing, metal materials have high processing cost, low machining efficiency, long processing cycle and property of the relatively large density. So some researchers consider using some non-metallic materials gradually as the processing material of the heat radiator. Because it has the properties of easy processing microstructure, easy molding and low cost.In this paper, a kind of microstructure heat radiator with high conductivity metal base as heat conduction unit and high heat dissipation polymer microstructure as cooling unit is put forward. Because metal has high conductivity coefficient and limited heat dissipation coefficient, and plastic the low conductivity coefficient of which is several tenths of metal has high dissipation coefficient and low conductivity coefficient, a new type metal-plastic composite microstructure heat radiator is put forward which has the advantage of both metal and plastic.In order to increase the specific surface area of heat radiator which affects the heat dissipation capacity, microstructure is added on the surface of the heat radiator which makes full of the property of plastic of easy molding microstructure.In this paper, the mechanism of theoretical and experimental study of the metal and plastic composite microstructure heat radiator is done. Metal and plastic composite conductive heat unit and plastic heat diffusion unit are modeled. The balance principle and matching method that the conductive heat ability and heat diffusion ability are matched are put forward. The necessity and importance of the microscale about plastic heat diffusion unit are researched.The heat transfer process of double composite layer is simulated, especially the effect of the thickness of the plastic layer and the thermal conductivity of plastic on the ability to conduct heat. The research result shows that because the thermal conductivity of the metal is much bigger than that of the plastic, so the ability to conduct heat is mainly decided by the thickness and the thermal conductivity of the plastic. The design principle that the conductive heat ability of the metal and the heat diffusion ability of the plastic are matched is put forward. According to this principle, the thickness of plastic layer should be about from 200μm to 300p.m.A kind of metal and plastic composite heat radiator with hemispherical microstructure is put forward. The simulation of the heat radiator based on FloEFD is done. Influence factors that affect the cooling efficiency of the heat radiator are gotten. The results show the main factors include material of the heat radiator, microstructure on the fin, thermal conductivity of plastic, radiation emission rate of plastic, size of hemisphere, inclination angle of the heat radiator. The results show specific surface area of hemispherical heat radiator is only associated with arrangement of hemispherical and has nothing to do with size of hemisphere. The limit specific surface area is 2. Bigger size of hemisphere can’t be chosen because of low thermal conductivity of the plastic. When the size of hemisphere is big, the heat can’t be transferred to the surface effectively. The trend that temperature on the surface of the hemisphere changes with the decrease of the size of the hemisphere becomes slower to a certain degree. At this moment, if the size of the hemisphere becomes small, the temperature doesn’t reduce obviously. However, the manufacture becomes difficult. Considering the cooling performance and manufacture cost, it is suitable that the size of hemisphere is about 2mm. It illustrates that microstructure on the surface is important.The heat conductive and heat transfer mathematical model of metal-plastic composite heat radiator is established. The influence rules of V groove apex angle, heat power, radiation emission rate and thermal conductivity of the plastic, natural convection coefficient and environmental temperature on the performance of the heat radiator are achieved. The result show the specific surface area is only associated with the V groove apex angle and has nothing to do with the height of V groove. Specific surface area is equal to the reciprocal of sine of the V groove half-apex angle. So, as long as the material’s stiffness can satisfy the use requirement, half-apex Angle can be taken as small as possible. In theory specific surface area can be any bigger. Bigger height of V groove can’t be chosen because of low thermal conductivity of the plastic. When the height of V groove is big, the heat can’t be transferred to the surface effectively. The trend that temperatures on the surface of the V groove change with the decrease of height of the V groove becomes slower to a certain degree. At this moment, if the height of V groove becomes small, the temperature doesn’t reduce obviously. However, the manufacture becomes difficult. When the specific surface area is increased, the condition that is beneficial to convection and radiation needs to be considered. The microstructure of the heat diffusion unit is beneficial to strengthen the convection and radiation. Because the microstructure array effectively avoids the high airflow resistance and multiple refraction radiation questions, the efficiency of the convection and radiation is improved observably. Considering the cooling effectiveness, the processing difficulty, structure stiffness, etc., micro V groove cooling unit is a very good choice.