高速列车制动盘表面对流传热特性

As a train gains speed, its kinetic energy and the heat energy produced in its breaking process increase greatly. The huge heat load produced by braking of the brake discs strongly affects the braking efficiency. Weak convective heat transfer on the surfaces of brake discs leads to various thermal cracks and braking failure. Convective heat transfer on the surfaces of brake discs is thus an important process that affects the performance of brake discs. There have been few studies on convective heat transfer on the surface of brake discs, and the models used in the reported investigations do not reasonably match the real working conditions of the brake discs. It is well known that the models determine the fluid flow, and the fluid flow determines the convective heat transfer. It is thus difficult to apply the reported results to the real design of brake discs. Against this background, the main contributions of the present paper are the establishing of a flow model reasonably matches the actual working conditions of brake discs and the measurement of local and average convection heat transfer characteristics. To establish the model, in the experimental process the brake discs were drawn by rolling wheels that rolled on a circular orbit. To obtain the convection heat transfer characteristics, the analogy of the naphthalene sublimation technique of heat/mass transfer is adopted. The local Nusselt number on the surface of a brake disc decreases along the radius because convective heat transfer is mainly enforced by fluid flow induced by the brake disc. Because of the weaker effect of the ground surface, the average Nusselt number for the surface of a break disc is larger than that of a rotating disk in cross flow at the same Reynolds number. The average Nusselt number for the surface of a brake disc is larger than that for a rolling wheel at the same Reynolds number. The correlations of the local and average Nusselt numbers with the Reynolds number are established.