分类: 动力与电气工程 >> 工程热物理学 提交时间: 2018-01-24 合作期刊: 《热科学学报》
摘要: To investigate the role of a single shield on steady temperature measurement using thermocouples in hot air flow, a methodology for solving convection, conduction, and radiation in one single model is provided. In order to compare with the experimental results, a cylindrical computational domain is established, which is the same size with the hot calibration wind-tunnel. In the computational domain, two kinds of thermocouples, the bare-bead and the single-shielded thermocouples, are simulated respectively. Surface temperature distribution and the temperature measurement bias of the two typical thermocouples are compared. The simulation results indicate that: 1) The existence of the shield reduces bead surface heat flux and changes the direction of wires inner heat conduction in a colder surrounding; 2) The existence of the shield reduces the temperature measurement bias both by improving bead surface temperature and by reducing surface temperature gradient; 3) The shield effectively reduces the effect of the ambient temperature on the temperature measurement bias; 4) The shield effectively reduces the influence of airflow velocity on the temperature measurement bias.
分类: 核科学技术 >> 核材料与工艺技术 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Diffusion behaviors of Se(IV) and Re(VII) in bentonite were investigated by a through-diffusion method in nitrate, sulfate, carbonate and silicate solutions. SEM-EDS analysis showed that Se(IV) was reduced to red precipitate Se(0) by sulfite. Se(IV) was sorbed on bentonite with distribution coefficient Kd of (2.65.3)10-4 m3/kg in sulfite, nitrate and sulfate solutions, whereas it was hardly sorbed in carbonate and silicate solutions. The effective diffusion coefficients were De= (0.817.0)10-11 m2/s for Se(IV) and De= (1.44.4)10-11 m2/s for Re(VII). The De value of Se(IV) exhibited a dependence on the inorganic salts in the order of sulfite nitrate sulfate > silicate > carbonate, whereas the salts had insignificant effect on Re(VII) diffusion. The results suggest that the discrepancy in diffusion mechanism may lead to the different impact of the salts on the diffusion of Se(IV) and Re(VII) in GMZ bentonite.