Water-air flow in straight pipes and across 90° sharp-angled mitre elbows
Water-air flow in straight pipes and across 90° sharp-angled mitre elbows
复制标题
DOI：
10.1016/j.ijmultiphaseflow.2019.06.005
复制
发表时间：
2019-09-01
影响因子：
3.8
通讯作者：
Ricco, Pierre
中科院分区：
文献类型：
--
作者：
Al-Tameemi, Wameedh T. M.;Ricco, Pierre
通过高精度摄像机观察流型和测量压降，研究了水平和垂直直管中的水-气流动以及90度尖角斜接弯头中的水-气流动。本文研究了三种管径的水-气两相流动，约600种工况，其表观流速范围为j(L)*，水=0.3-1m/S，空气j(G)*=0.15-34m/S。弯头上游的管道部分始终水平放置，而急弯下游的管道部分随着水流向上移动而水平或垂直定位。塞状流、段塞流、段塞流、段塞流、环状流在水平直管中可见，而段塞、搅动和环状流则记录在急弯下游的垂直直管中。对于水平方向的直管，Mandhane图(Mandhane等人，1974)和Hewitt-Roberts图(Hewitt和Roberts，1969)对于垂直方向的直管，这些模式得到了很好的预测。讨论了流体流过斜接弯头时流型的变化。在垂直向上流动中，基于表面流速的雷诺数比文献报道的垂直向下流动的雷诺数大得多的情况下，观察到了多层膜流动结构。通过量纲分析得到了描述流经直管和弯头的无量纲参数。证明了对于给定的几何形状，水-空气流动的流型和压降系数的严格表示方法是以固定弗劳德数的空气和水的表观速度为基础的雷诺数空间，因为流动是不可压缩和等温的。通过将地图按比例表示，改进了对沿管道直线部分的流型的预测。流经弯头的流型用重新缩放的Mandhane图来表示，这是第一次同时表示弯头的上游和下游的流型。得到了流经水平管、垂直管和弯头的水-气比例压降的新的基于图形的经验关联式。关联式是基于流型的，并不依赖广泛使用的预测模型，因此比目前文献中可用的模型更准确地预测压降。皇冠版权所有(C)2019由爱思唯尔有限公司出版。保留所有权利。
Water-air flow in horizontal and vertical straight pipes and through 90 degrees sharp-angled mitre elbows is investigated by visualizing the flow patterns by means of a high-precision camera and by measuring the pressure drop. The flow is studied in pipes with three diameters for about six hundred conditions of water-air flows, characterized by superficial velocities in the ranges of j(L)*, = 0.3-1 m/s for water and j(G)* = 0.15-34 m/s for air. The portion of the pipe upstream of the elbow is always positioned horizontally, while the portion of the pipe downstream of the sharp bend is oriented horizontally or vertically with the flow moving upward. Plug, slug, slug-annular, and annular flows are visualized in horizontal straight pipes, while slug, churn, and annular regimes are recorded in vertical straight pipes downstream of the sharp bend. These patterns are well predicted by the Mandhane map (Mandhane et al., 1974) for horizontally oriented straight pipes and by the Hewitt-Roberts map (Hewitt and Roberts, 1969) for vertically oriented straight pipes. The changes of the flow patterns as the fluids pass through the mitre elbows are discussed. A multiple membrane flow structure is observed in the vertical upward flow at much higher Reynolds numbers based on the water superficial velocity than in the vertical downward case previously reported in the literature. A dimensional analysis is employed to obtain the non-dimensional parameters that describe the flows through the straight pipes and across the elbows. It is proved that a rigorous way to present the flow regimes and the pressure-drop coefficients of the water-air flow for a given geometry is the space of the Reynolds numbers based on the superficial velocities of air and water for fixed Froude number because the flow is incompressible and isothermal. By expressing the maps in scaled form, the prediction of the flow patterns along the straight portions of the pipe improves. The flow patterns through the elbows are expressed in terms of rescaled Mandhane maps, which, for the first time, simultaneously represent the flow patterns both upstream and downstream of the elbows. New pattern-based empirical correlations are obtained for the scaled pressure drops for the water-air flows through the horizontal and vertical pipes and through the elbows. The correlations are based on the flow patterns and do not rely on widely used prediction models, thereby predicting the pressure drop more accurately than the models presently available in the literature. Crown Copyright (C) 2019 Published by Elsevier Ltd. All rights reserved.