【摘要】 超临界流体技术是新兴的化工技术之一,传热是其工程应用研究的重要方向。以二氧化碳作为超临界流体的代表,通过试验得到密闭竖直细管内二氧化碳在超临界状态下自然对流的传热特性。探索了试验段管径、加热段加热功率不变,试验工质在不同压力的条件下的传热特性。研究表明:竖直密闭细管内的超临界流体二氧化碳的传热方式以自然对流为主。加热试验段,当试验段壁温升高到超临界温度以上,密闭空间内超临界状态的二氧化碳在稳定操作条件下,通常会发生"脉动"传热现象。试验段充入二氧化碳后,加热段的测温点温度降低3℃,而在冷凝段测温点温度却提升了近6℃,各测温点间温度差减小,即试验段的温差呈现"展平"现象。说明在超临界压力下,二氧化碳的传热性能好于常规状态。更多还原

【Abstract】 Supercritical fluid technology is one of new chemical engineering techniques, in which heat transfer is of importance in technical application. The natural convection heat transfer performance of supercritical carbon dioxide in a vertical pipe was presented by experiments, in which a given diameter of tube and heating power were set, different pressures were considered. The results show that natural convection is a fundamental heat transfer mode for supercritical carbon dioxide. As wall temperature of experiment segment is over supercritical temperature, “fluttering" heat transfer of supercritical carbon dioxide in closed space is usually found under steady operating conditions. 3 ℃ drop of measure point in heating segment and 6 ℃ increase of measure point in condense segment as well as decrease of temperature difference between measure points, namely “panning" phenomenon, are usually found as carbon dioxide is charged. It also shows that heat transfer performance of carbon dioxide under supercritical state is better than under general state.更多还原