Structure Design And Heat Dissipation Performance Of New Type Heat Pipe Air Duct Brake Disc

Brake discs have been widely used in family passenger vehicles,among which ventilated brake discs occupy a major position.The ventilated discs will generate a lot of heat under high-speed or frequent braking.If the heat cannot be dissipated in time,the braking system will appear a series of thermal decay phenomena such as softening of the friction lining material,thermal cracking of the brake disc metal and hot spots,which seriously affect the braking performance of the vehicle,and the braking ability is greatly reduced.In order to ensure safe driving of the vehicle and avoid thermal degradation of the brake system,the heat dissipation of the ventilated brake disc must be strengthened.At present,there are basically two research directions for the heat dissipation of brake discs.One is to optimize the appearance and structure of brake discs.By perforating and scoring,the shape,structure and number of ventilated brake disc air duct blades are changed to enhance the replacement.Thermal effect,the other is to solve the safety problem caused by brake overheating by replacing high temperature resistant carbon fiber ceramics and other composite materials.In recent years,a heat pipe brake disc based on a single disc has also been proposed,but it is lacking in structural reliability and heat dissipation capability.In view of the insufficient heat dissipation capacity of the current ventilating discs,this thesis proposes a new heat pipe ventilated brake disc with a built-in integral heat pipe to strengthen its heat dissipation and braking capabilities and provide guarantees for safe driving and the preservation of people’s lives and property.The new heat pipe type ventilation brake disc creatively integrates the heat pipe into the ventilation disc,making the existing ventilation disc a built-in integral heat pipe ventilation disc to the greatest extent.In order to avoid the heat pipe ventilation disc from being deformed under pressure during operation,the pressure-bearing disc is evenly arranged inside it structure.In order to optimize its heat dissipation capacity,a flow aid arch is set at the largest diameter of the hollow to facilitate the circulation of the working fluid,and a capillary evaporation surface is set on the friction surface corresponding to the inner cavity wall to facilitate the evaporation of the working fluid and avoid dry burning of the friction surface.Ventilation holes are provided in the corresponding parts of the pressure block to increase the heat dissipation area and increase the ventilation volume.Numerical calculations based on Computational Fluid Dynamics(CFD)are carried out for the new heat pipe ventilation plate and the current solid ventilation plate,and the relationship between the heat transfer performance of the new heat pipe ventilation plate and the filling rate,ventilation holes and heating power is obtained.At the same time,the heat transfer performance of the new heat pipe ventilation plate is compared with the existing solid ventilation plate with the same structure based on numerical calculation,and the data of the heat dissipation performance improvement of the new heat pipe ventilation plate is obtained.The following conclusions are drawn through numerical simulation:The best liquid filling rate of the three heat pipe air duct brake discs with low heat flux density(≤15000W/m2)is 35%,and the best liquid filling rate at high heat flux density(>15000W/m2)The filling rate is 40%,and the heat pipe brake disc can achieve the best heat dissipation performance.The heat dissipation holes have a certain effect on the heat dissipation of the heat pipe brake discs.The heat pipe brake discs with inclined heat dissipation holes have a maximum disc surface temperature of 16 K lower than the heat pipe brake discs without heat dissipation holes,which effectively reduce the disc surface temperature.As the speed of the brake disc increases,the convective heat transfer coefficient between the brake disc and the air increases.Under the same heat dissipation area,the convective heat transfer increases and the disc surface temperature decreases.In terms of the temperature uniformity of the brake disc surface,as the heat flow density increases,the overall temperature of the disc surface increases,and the heat conduction resistance of the disc surface gradually decreases.The heat dissipation performance of the heat pipe brake disc gradually increases,and when the heat flow density increases to a certain value,the heat transfer performance of the heat pipe brake disc gradually reaches the maximum Excellent state.The filling rate has a certain influence on the uniform temperature performance of the heat pipe.At the best filling rate,the heat pipe has the best temperature uniformity on the disk surface.Due to the existence of the heat dissipation hole structure,the convective heat exchange effect from the heat dissipation hole is enhanced.Therefore,the brake disc surface temperature of the brake disc with the heat dissipation hole is lower,but the temperature around the heat dissipation hole is much different from the temperature of other parts of the disc surface,which reduces the disc surface temperature.With the increase of the heat flow density,the temperature difference between the periphery of the heat dissipation hole and other disk surface is intensified,so there is a large disk surface temperature difference under 20000W/m2.The effect of the speed on the temperature uniformity of the disc surface is reflected in the increase in the speed of the brake disc,the overall convective heat transfer coefficient of the brake disc increases,the heat exchange increases,and the overall temperature of the disc surface decreases.However,due to the increase of the speed,the heat dissipation effect of the cooling holes is more obvious,so the speed increases the temperature uniformity of the disk surface decreases.Compared with ordinary solid brake discs,as the heat flow density increases,the disc surface temperature difference between the heat pipe brake disc and the solid brake disc is more significant.Under 20000W/m2,35%fluid filling rate heat pipe disc can be 49K lower than the average temperature of the solid brake disc.The cooling effect is significant;the temperature uniformity of the solid brake disc is better than that of the heat pipe brake disc.Appropriately increasing the internal pressure structure of the heat pipe disc and the number of air duct blades can effectively reduce the disc surface temperature and improve the disc surface temperature uniformity.