超临界甲烷在绕管内冷凝流动换热特性数值模拟

Numerical simulation of condensation heat transfer characteristics of supercritical methane flowing in helical coiled tube

超临界流体甲烷在绕管内冷凝流动换热时,因准临界点附近流体物性的剧烈变化和离心力影响使得换热过程更为复杂。采用数值模拟方法分析甲烷在绕管内流动换热特征,研究选取一根缠绕两圈的绕管,每隔60°设置一个监测面,监测各个截面上的Pr数、温度、湍流强度等,探讨了各个截面上甲烷的流动换热特性。结果表明:靠近绕管外侧流体主流速度、压力明显高于绕管内侧流体速度和压力,密度分布与速度分布正好相反;管内流体流动时在离心力、浮升力共同的作用下,形成了圆管外周顺时针和圆管中心逆时针两个不同旋转方向的二次流;靠近绕管内侧流体的传热效果好于外壁面的传热效果;在准临界点附近的流体,物性变化对换热系数的影响占据了主要地位。

The flow and heat transfer process of supercritical fluid methane is more complicated due to the drastic change of fluid physical properties near the quasi-critical point,with the influence of centrifugal force in helical coiled tube.The characteristic of the flow and heat transfer of supercritical methane cooled and condensed in the helical coiled tube was analyzed using numerical simulation method,in which a helical coiled tube with two circlesis was selected as study objective.At every 60°cross-section a monitoring surface was set to monitor Pr number,temperature and turbulent intensity of fluid.The flow and heat transfer characteristics of supercritical methane on each monitoring surface were studied in detail.The results show that the main flow velocity and the pressure of fluids near the outside of the tube are obviously higher than those near the inside of the tube.The density distribution of fluids in the tube is just opposite to their velocity distribution.On the combination influence of centrifugal and floating lift forces,the fluid in the tube forms a secondary flow with two different rotation directions.The outside fluids in the circular tube rotate in a clockwise rotation direction while the central fluids do in a counterclockwise direction.The heat transfer coefficient of the fluids near the inside of the tube is higher than those at the external wall.The influence of fluid properties on heat transfer coefficient in the vicinity of the quasi-critical point plays a dominant role.