The heat transfer between an airway and the air flowing though it is an unsteady problem. The governing equation of unsteady heat transfer was solved using the method of separation of variables. The solution is an inf...The heat transfer between an airway and the air flowing though it is an unsteady problem. The governing equation of unsteady heat transfer was solved using the method of separation of variables. The solution is an infinite series including Bessel functions. The theoretical solution was analyzed by solving for the positive roots of the transcendental equation by iteration. The dimensionless surface temperature of the sur- rounding rock is only affected by the Bi number but not by the thermo-physical coefficients of the rock. The dimensionless coefficient of heat transfer, k, decreases with the Fo number similarly to the influence of the Bi number on k. A formula for determining the fully developed stage (FDS) suitable for unsteady heat transfer in the airway is proposed. The FDS from theoretical analysis occurs with Fo from 1.6 to 2. The ratio of excess temperature in the surrounding rock is independent of the initial conditions and only dependent on the Bi number and the relative position in the airway, at the FDS. The calculation error is large when using just the first term from the complete series when Fo is from 2 to 12. Five terms give a solution approximately equal to that found using the complete series. The first term could replace the complete series only when Fo is greater than 12. The FDS plays an important role in predication of the temperature field of the surrounding rock and in simplified calculations.展开更多
Experiments were conducted to investigate the cooling manner of an ultra-thick hot aluminum alloy plate during multistage quenching. Cooling curves and heat flux curves of different rapid quenching flux varied from 23...Experiments were conducted to investigate the cooling manner of an ultra-thick hot aluminum alloy plate during multistage quenching. Cooling curves and heat flux curves of different rapid quenching flux varied from 23 to 40 L min^(-1) and were analyzed in detail. In this investigation, cooling process was divided into the following four steps:(I) starting step,(II) rapid cooling step,(III) slow cooling step, and(IV) stopping step. Based on the curves, the calculation method for surface transfer coefficient was provided, and the effects of coefficient on surface temperature and quenching flux were discussed. Results showed that the transfer coefficient disagreed with heat flux and that it is a nonlinear function of surface temperature. The highest coefficient was observed not in the rapid cooling step with the largest heat flux but in the slow cooling step with lower heat flux. The coefficient increased with surface temperature ranging from 480 to 150°C, and a coefficient peak appeared in the temperature range of 150–100°C. The coefficient also increased with quenching flux. Finally, a simulation was performed using the finite element method to verify the reliability of the coefficient results, which showed good agreement with the measurement values.展开更多
基金provided by the Postdoctoral Science Foundation of China (No. 2011M500974)Fundamental Research Funds for Central Universities (No. 2011QNA16)+1 种基金Postdoctoral Foundation of state key laboratory for GDUE (No. PD1101)Natural Science Foundation for Young Scholars of SMCE, CUMT(No. lj2010qnjj004)
文摘The heat transfer between an airway and the air flowing though it is an unsteady problem. The governing equation of unsteady heat transfer was solved using the method of separation of variables. The solution is an infinite series including Bessel functions. The theoretical solution was analyzed by solving for the positive roots of the transcendental equation by iteration. The dimensionless surface temperature of the sur- rounding rock is only affected by the Bi number but not by the thermo-physical coefficients of the rock. The dimensionless coefficient of heat transfer, k, decreases with the Fo number similarly to the influence of the Bi number on k. A formula for determining the fully developed stage (FDS) suitable for unsteady heat transfer in the airway is proposed. The FDS from theoretical analysis occurs with Fo from 1.6 to 2. The ratio of excess temperature in the surrounding rock is independent of the initial conditions and only dependent on the Bi number and the relative position in the airway, at the FDS. The calculation error is large when using just the first term from the complete series when Fo is from 2 to 12. Five terms give a solution approximately equal to that found using the complete series. The first term could replace the complete series only when Fo is greater than 12. The FDS plays an important role in predication of the temperature field of the surrounding rock and in simplified calculations.
基金supported by the National Basic Research Program of China(Grant No.2012CB619500)the Major State Research Program of China(Grant No.2016YFB0300901)+1 种基金the National Natural Science Foundation of China(Grant No.51375503)the BaGui Scholars Program of China’s Guangxi Zhuang Autonomous Region(Grant No.2013A017)
文摘Experiments were conducted to investigate the cooling manner of an ultra-thick hot aluminum alloy plate during multistage quenching. Cooling curves and heat flux curves of different rapid quenching flux varied from 23 to 40 L min^(-1) and were analyzed in detail. In this investigation, cooling process was divided into the following four steps:(I) starting step,(II) rapid cooling step,(III) slow cooling step, and(IV) stopping step. Based on the curves, the calculation method for surface transfer coefficient was provided, and the effects of coefficient on surface temperature and quenching flux were discussed. Results showed that the transfer coefficient disagreed with heat flux and that it is a nonlinear function of surface temperature. The highest coefficient was observed not in the rapid cooling step with the largest heat flux but in the slow cooling step with lower heat flux. The coefficient increased with surface temperature ranging from 480 to 150°C, and a coefficient peak appeared in the temperature range of 150–100°C. The coefficient also increased with quenching flux. Finally, a simulation was performed using the finite element method to verify the reliability of the coefficient results, which showed good agreement with the measurement values.
