Study Of Convection Heat Transfer Enhanced By Corona Wind Based On EHD Effect

Semiconductor components are the hardware foundation of today's electronic information era,which makes their reliability crucial.However,as the operating temperature rises,their failure rate increases almost exponentially.In the heat dissipation process of components,the air-side thermal resistance is generally the largest of all thermal resistances.Therefore,convection heat transfer needs to be enhanced urgently.Based on the electrohydrodynamics(EHD)effect,the corona wind technology can significantly improve the convection heat transfer coefficient,and avoid some disadvantages of traditional fans,which makes it has been widely studied.Its basic principle is to use an emitting electrode with a small radius of curvature and a collecting electrode with larger dimensions to compose an EHD device.When a sufficiently high voltage is applied to the emitting electrode,the air near it can be ionized and corona wind blowing toward the collecting electrode is generated under the action of the electric field force.With the support of the National Key R&D Program of China,this paper conducts the mechanism research,experimental study,and application investigation on corona wind-enhanced convection heat transfer to meet the high-efficiency and high-reliability heat dissipation requirements.In the mechanism research,the electric field,velocity field,and temperature field in a wire-plate electrode configuration are obtained through numerical simulation.Based on the field synergy theory of convection heat transfer,the angle between the velocity vector and temperature gradient vector,also called the synergy angle,is quantitatively analyzed in different cases.The wall temperature distribution of the heat sink is jointly affected by the air velocity and the synergy angle.The convection heat transfer can be enhanced by increasing the flow velocity or decreasing the synergy angle.When the flow velocity is very low,the synergy angle plays a decisive role in the heat transfer performance.In the experimental study,the emitting electrode is a wire and the collecting electrode is a divergent two-finned heat sink,which is also a type of wire-plate electrode configuration.The variable parameters are electrode voltage,voltage polarity,wirebase distance(distance between the wire electrode and fin base),wire diameter,fin included angle,and heating power.The target parameters are corona current,corona wind velocity,enhancement ratio(ER)of convection heat transfer coefficient,and coefficient of performance(COP)of the EHD device.At the same time,numerical simulation is used to analyze the influence mechanism of parameter changes on experimental results.Some experimental parameters have quite clear influences,such as raising electrode voltage or reducing wire diameter can always increase corona current,thus improving corona wind velocity and enhancing convection heat transfer.However,the effect of changing wire-base distance on heat transfer is more complex.As the wire electrode moves from the fin base to the open end of the heat sink,the convection heat transfer coefficient increases first and then decreases.Besides,the variation of the fin included angle changes both the electrode spacing and the dimensions of the flow channel,which affects the corona discharge and air flow at the same time,making the heat transfer show different characteristics.In this paper,the causes of variation in convection heat transfer performance are analyzed from two perspectives: flow characteristics and field synergy.The energy efficiency of an EHD device can be evaluated by COP,which is the ratio of heat flux of convection heat transfer to corona power consumption.In this paper,the corona power consumption has a decisive influence on the COP.The lower the corona power consumption,the higher COP.However,low corona power consumption means weak corona wind,so the highest COP and the maximum ER cannot be achieved simultaneously.Since the corona power consumption of this EHD device is very small,it is not necessary to pursue an excessively high COP.Increasing the convection heat transfer coefficient can reduce the cost of heat sinks and prolong the lifetime of electronic components,which is also an embodiment of economy in the whole system.In this experiment,the maximum ER is 4.17 and the highest COP is 144.3.In the final application investigation,a 12-finned sunflower heat sink is used as the collecting electrode,which is assembled into a lamp with an LED light source.Twelve wire electrodes are respectively placed in each fin gap to conduct the experimental study on corona wind-enhanced convection heat transfer of the LED lamp.The experiment has two purposes,one is to obtain the performance of convection heat transfer enhanced by corona wind,the other is to investigate whether the high voltage and current pulses in the corona discharge affect the original optical parameters of the lamp.The results show that corona wind increases the convection heat transfer coefficient by a maximum of 2.14 times when compared with the natural convection,and the luminous efficiency and electro-optic conversion efficiency are also improved due to the decrease of the light source temperature.By comparing the spectrum distribution,chromaticity diagram,and correlated color temperature of the light source with and without corona wind,no influence of the discharge process on the optical parameters of the lamp is found.