Experimental Study Of Transient Heat Transfer Coefficient At The Rail Surface

Because of the inevitable friction in wheel/rail contact area, when the train passes over the rail, the friction heat is generated and mainly stored in wheel/rail contact area surface. If it is not lost timely and effectively, the accumulation of heat can significantly improve rail surface temperature. It will cause the physical and chemical characteristics change of wheel/rail contact region material, such as the change of material organization structure, material strength decrease; accelerating material mechanical wear and developing noise. What is more, it leads to crack and stripping damage of the wheel/rail surface. On the other hand, the seamless rail restricts rail to lengthen and shorten freely, as a result, the thermal stress and mechanical stress are almost in the same order of magnitude. These factors have an important impact on trains safely runs. As the increase of train speed and axle load, braking urgently and accelerating traction of train frequently, as a result, a large amount of friction heat greatly improves temperature of the wheel/rail contact area surface. So running environment of train becomes more and more deteriorating, which has a great effect on comfortable, stable and safe operation of train.This damage is mainly caused by high temperature, which is generated by friction heat of wheel/rail contact surface. However, the frictional heat loss greatly depends on the convective heat transfer. When the train passes over the rail, the inevitable temperature rise of wheel/rail contact area is related to the transient convective heat transfer coefficient around the wheel/rail contact area; the transient convective heat transfer coefficient on the surface of rail is very important to impact on the temperature field and temperature rise of the rail. Therefore, to get the transient convective heat transfer coefficient of around the wheel/rail contact area is very important, which has theoretical and practical significance for train safe running and plays an important role in maintenance and safe use of the rail, timely and accurately mastering the dynamic temperature on the surface of rail. Therefore,the paper mainly focuses on the study of the transient convective heat transfer coefficient on the rail surface,when train passes over the rail rapidly.The thesis based on learning the related literature at home and abroad, analyzes the heat transfer mechanism of wheel/rail contact model, introduces the heat transfer physical model of rail surface, designs the experiment system of studying transient convective heat transfer characteristics on rail surface, depending on the Newton cooling formula and also designs experimental wheel/rail, according to the real train model and similar principle. At the same time, a series of measures are taken to exclude the electromagnetic interference produced by inverter and a device is designed to locate the position of simulative wheels, when experiment is going on. The transient convective heat transfer characteristic on the rail surface is investigated at different speed of the simulative wheels. It obtains a series of reliable experimental results. After analyzing the experimental data, the main conclusions are drawn as follows:(1) When the rolling wheel passes over the rail, the transient heat transfer coefficient on the surface of the rail presents the similar sine rule along with the time change. Then it will return to a stable value again.(2) The transient heat transfer coefficient on the surface of the rail depends on the speed of the wheel on the sidelines of two adjacent wheels passing over the rail in sequence, and it increases with the speed of the wheel increasing.(3) The transient heat transfer coefficient on the surface of the rail depends on the speed of wheel and heat transfer space of the wheel/rail.