输送LNG的真空保温管道的换热研究

真空保温技术广泛应用于LNG的储藏和运输领域,利用真空层进行隔热是一种有效的保温手段。模拟研究了带有聚四氟乙烯支撑环的三维输送管道的散热过程,讨论了真空层压力、环境温度、对流换热系数对散热性能的影响规律,并与热阻分析结果进行了对比验证。结果表明:随着真空层压力从0.001 kPa升至5.33 kPa,换热量从83.82 W升至124.72 W,0.001 kPa到2 kPa段的换热量升高的最快。随着外界温度从268.15 K升至298.15 K,换热量从97.54 W升至120.56 W,并且呈线性增长趋势。随着外界对流换热系数从5 W/(m^2·K)增至25 W/(m^2·K),换热量从112.1 W增至127.8 W。管间区域的空气在上方形成一个温度为290 K左右的高温区,下方形成一个温度为80 K左右的低温区,两区域之间形成环流,环流中部的空气流动速率最快为0.26 m/s。

Preparation of High-Entropy Alloy-Ceramic Coating Compos-ites on Steel Surfaces by Combined Process and Their Mechanical Properties

A combined process of molten salt electro-deoxidation and vacuum hot-pressing sintering was proposed to prepare AlCrFeNiTi_(x) high-entropy alloy(HEA)-TiN ceramic coating composites on low-carbon steel surfaces,where nitrides were introduced from BN isolater between graphite mold and HEA powders.The effect of Ti content on the microstructure,ultimate tensile strength,hardness,and wear resistance of the composites was investigated,and the bonding mechanism was elucidated.Results demonstrate that the composites have excellent hardness and wear resistance.The hardness of composites is significantly increased with the increase in Ti content.The extremely high wear resistance is attributed to the extremely high melting point and high thermal hardness of TiN,which can effectively prevent oxidation deformation of the worn surface.