变曲率螺旋管内两相流型变迁模拟研究

Simulation of Two-phase Flow Pattern Transition in Helical Tubes With Variable Curvature

为进一步提升蒸汽发生器螺旋换热管的传热传质性能,本文提出了一种盘管曲率周期性变化的变曲率螺旋管改进方案。并对变曲率螺旋管内气液两相流动特性开展了数值模拟研究。基于有限元方法,建立了单根变曲率螺旋管内流体六面体结构化网格,采用VOF模型捕捉相界面,分析管内液相流场分布特性。研究发现,在同一根变曲率螺旋管内不同位置管段的两相分布与流型并不相同,部分管段出现了分层流-波状流-塞状流的间歇性流型变迁现象。这是由于盘管曲率的周期性改变,使得管内液相所受离心力不断改变,两相分布在空间位置及时间分布上均不断变化,产生了两相流型变迁的现象。

To further advance the performance of heat and mass transfer in the helical heat exchange tubes of the steam generator,this paper presents an enhancement plan involving a helical tube design featuring periodic curvature changes.A numeric simulation study was conducted to examine the characteristics of a gas-liquid two-phase flow within tubes of varying curvature.By applying the finite element method,a hexahedral structured grid was established for the fluid flow within a single helical tube.The Volume of Fluid(VOF)model was utilized to capture the phase boundary,and the characteristics of the in-tube liquid phase flow field distribution were analyzed.The research found differing two-phase distributions and flow patterns in different sections within the same helically-curved tube,with some sections displaying an intermittent transition phenomenon from stratified flow to wavy flow,and then to plug flow.This phenomenon is attributed to the periodic variations in coil curvature,which in turn continuously alters the centrifugal force experienced by the in-tube liquid phase,leading to a dynamically changing two-phase distribution in both spatial and temporal contexts.