Research On Convection Heat Transfer Coefficient On The Surface Of Ventilated Brake Disc And Optimization Of Heat Dissipation Performance

The automobile brake system is one of the four major systems of the automobile chassis(transmission system,driving system,steering system,braking system).Its main function is driving deceleration,even parking.The automobile brake system is mainly composed of the driving mechanism and the brake.In the process of automobile braking,the kinetic energy of the vehicle is mainly converted into internal energy by the friction between brake disc and brake shoe,which makes the temperature of the brake disc and the brake shoe rise sharply,and the excessive temperature will lead the brake to produce the thermal decay,and even result in braking failure.Therefore,lifting the cooling performance of the brake disc and brake shoe is essential.Ventilated brake disc have ventilation groove structure,which can make the air get centrifugal force and accelerate convection between the air and the disc.This make ventilated brake disc has better heat dissipation,heat fading resistance performance than the solid disk and has been widely used.A three dimensional model is set up based on the actual size of the front ventilated brake disc of a certain type of vehicle in this thesis.First of all,in view of the convection heat transfer problem of ventilated brake disc and air,the convective heat transfer characteristics of each main heat dissipation surface are analyzed,based on the principle of forced convection heat transfer and the criterion equation,the mathematical model of convective heat transfer coefficient of the side,ventilating groove,cap surface and edge surface of the ventilated brake disc is established respectively.Secondly,numerical simulation method and test method are used to verify the accuracy of the mathematical model of the surface convection heat transfer coefficient of the ventilated brake disc.The fluid-solid coupling model of brake disc and air is established,and the surface convective heat transfer coefficients of the main heat dissipation surfaces of the brake disc under different speed are calculated by fluent software,and the accuracy of the mathematical model is verified by comparing with the mathematic model.By using the finite element analysis method of temperature field,setting the thermal load and velocity boundary condition,the mathematical model of the surface convective heat transfer coefficient of the ventilated brake disc is taken as the heat dissipation boundary condition,and the temperature change of the brake disc under 15 times cycle braking condition is calculated.The brake electric inertia test bench was used to carry out 15 cyclicbraking experiments to measure the temperature change of the brake disc.By comparing the simulation value with the experimental value,the accuracy of the mathematical model of convective heat transfer is indirectly verified.Finally,the air flow field in the ventilation groove of the ventilated brake disc under different speed is analyzed,and the structure of the airflow channel is optimized.Based on the mathematical model of the heat transfer coefficient of the main heat dissipation of the brake disc,the mathematic model of the influence of the width and number of the airflow path on the cooling rate of the brake disc is established,and the optimal runner design scheme is found.The temperature of the optimized brake disc during the 15 cycle braking process is calculated,the maximum temperature in the braking process is reduced obviously.These methods play a guiding role in optimizing the heat dissipation design of the ventilating brake disc.