Experimental Study On The Heat Transfer Characteristics Of The Brake Disc Of A High-speed Train

With the increase of train speed, the kinetic energy of train increases dramatically, meanwhile the heat energy produced by breaking process increases greatly. The huge heat load within a short time generated by the breaking of the brake discs, it makes the brake disc have great temperature gradient. If the convective heat transfer on the surfaces of the brake disc is very weak, it will lead to various thermal cracks, braking failure,and so on. Therefore, the convective heat transfer coefficients on the surface of the brake discs affect the degree of heat dissipation in the process of braking of the break discs directly.There are two kinds of motions in the process of breaking. Firstly, it rotates at the same speed with the wheel. Secondly, it moves with the same translational velocity of trains. The existence of the ground has great effect on convective heat transfer on the surface of the brake disc. It is well known that the models determine the fluid flow, and the fluid flow determines convective heat transfer. Thus, the reported results on this topic meet difficulties to apply in real design of the breaking discs. In order to overcome these difficulties, the main works of this paper are to establish flow model that is similar to the actual working condition of the brake discs. To establish the model, in the experimental process the brake discs were drawn by rolling wheels that rolled on a circular orbit.This paper mainly concludes two parts; firstly, with naphthalene sublimation technology, the local and average Nusselt number on the surface of brake discs is obtained by designing experiment specimen of different diameters. Secondly, designing the experimental specimens of brake disc internal channels according to certain proportion, the rule of the internal average Nusselt number is gutted using touch naphthalene technology.In order to research the convection heat transfer characteristics of the surface and internal channel of brake discs, the naphthalene sublimation technique of heat / mass transfer analogy method is used. The conclusions of local and average heat transfer characteristics on the surface of a rolling break disc can be drawn:（1） The local Nusselt numbers on the surface of break disc decreases along the Radius direction.（2） The average Nusselt numbers on the surface of a rolling break disc increases with increasing Reω.（3） The ratio of local Nusselt number Nur to the average Nusselt number Nu on the surface of the brake disc has decreasing trend with the r/R, and the corresponding correlation is obtained,Nu_r=0.709Nu（r/R）^-0.380.（4） Because of the influence of the ground, the average Nusselt numbers on the surface of break disc is larger than that of a rotating disk in crossflow under the same Reω.（5） The average Nusselt number on the surface of a rolling break disc is larger than that on a rolling wheel under the same Reω.（6） When the diameter of the rolling wheel is same, the smaller diameter of the small test wheel is, the better its convective heat transfer performance is.（7） When the diameter of small test wheel is same, under the same Reω, the larger diameter of rolling wheel is, the greater Nu of test wheel is and the better convective heat transfer characteristics on the surface is.（8） The correlations between convective heat transfer coefficient h on the surface of the small test wheel and angular velocity ω is h=1.8252C^0.779.（9） The average Nu number on the internal channel of brake disc increases with the increasing of Reω and the correlation between the average Nu and Reω is obtained.