環形鰭片在不同接觸壓力與熱導下之熱應力分析

The purpose of this paper is to investigate the heat transfer and thermal stress of a variable temperature inner tube for transporting saturated water vapor and its external interference annular fin under different contact pressures. The related variables include interference between the fin and the inner tube, the fin material and fin radius ratio, to obtain temperature and thermal stress distribution under different variables, as well as possible damage beyond the design limit, to confirm that the system can operate within the scope of safety design. First, the contact pressure between the two interfaces is obtained by considering the temperature boundary condition of the inner tube wall varying with time and the saturated vapor pressure at that temperature. Subsequently, contact thermal conductivity is calculated by Yovanovich's empirical formula, and then the thermal contact conductivity is used as the boundary condition of the fin to solve the temperature distribution curve. The distribution curve of thermal stress, including radial stress and tangential stress, is obtained from the temperature field. In this paper, the effects of various interferences and different ratios of fin diameters on temperature distribution, temperature difference at the interface, and thermal stress distribution of fins are discussed, as is the relationship between heat transfer efficiency and heat transfer capacity of fins in a steady state. Contact pressure affects contact thermal conductivity, while contact thermal conductivity affects the heat transfer efficiency of fins. The temperature disparity on the contact surface decreases with the increase in contact pressure. The interference can effectively narrow the temperature gap, and the stress field varies with the interference, the ratio of inner to outer radius, and the thermal expansion rate of the material itself. The greater the interference, the greater the radial stress near the contact surface, and the circumferential stress distribution is transformed from the pressure on the fin base to the tensile force at the fin tail end. This is because, when the effect of temperature change is less than that of displacement, the circumferential stress will present compressive force and vice versa; it will present tensile force. The greater the ratio of inner to outer diameter, the greater the stress in the circumference and radial direction.