Numerical study on conjugate heat transfer in laminar fully developed flow with temperature dependent thermal properties through an externally heated SiC/SiC composite pipe and thermally induced stress

摘要

This study presents numerical solutions of conjugate heat transfer in laminar, fully developed flow through an externally heated pipe and the thermally induced stress under high temperature conditions. For this purpose, a SiC/SiC composite and liquid metals (lithium and sodium) were considered as pipe material and fluid, respectively, Various flow cases were considered as: the lithium and sodium flows with constant thermal properties, CTPs, and with temperature dependent thermal properties, TTPs. The calculations were performed individually for a wide range of thermal conductivity of the solid (k_s = 10-100 W/mK stepped by 10 W/mK) and various mean pipe inlet velocities (U_m = 0.01-0.02 m/s stepped by 0.002 m/s) under both steady state and transient conditions. In order to keep the maximum relative temperature of the solid within the interval, θ_s = 190-200 K, also the temperature controlled heating case was performed. Furthermore, a computer program, applying the SIMPSON integration method to the obtained temperature distributions from the heat transfer calculations, has been developed to calculate numerically the thermal stress distributions. The temperature difference ratios, TDRs, which are the ratios of the difference of temperatures at the same point in both flow cases to the relative temperature at that point in the temperature dependent thermal property cases, in the lithium flow case are lower than those in the sodium flow case, and the averages of the TDRs in the solid, fluid and outlet regions are about 2% and 6-7% in the lithium and sodium flow cases, respectively. Although the increase of U_m substantially affects the relative temperatures, it does not affect very much the effective thermal stress. The maximum effective thermal stress ratios decrease exponentially with the increase of k_s. As the radial distance increases, the effective thermal stress ratios, having maximum values at the inner radius (r/D = 0.4), reduce to minimum values at almost r/D = 0.445 and then increase. The results of this study would serve to determine the temperature distributions and the thermally induced stresses in similar pipe flow applications.