Abstract:

Quick closing valve (QCV) method is a common means of calibrating gas holdup in gas-liquid two-phase flow test. Unreasonable selections of spacing between valves and trapping times in QCV could bring about large error in gas holdup measurement, particularly since the gas slug and liquid slug in slug flow present flow characteristics with random variability. In this study, an optimal design was proposed for measuring gas holdup using QCV method. The cross-correlation velocity of gas-liquid two-phase slug flow was measured based on the signals between axially upstream and downstream probes. Then, the lengths of gas slug and liquid slug were extracted from the upstream probe signals under different flow conditions. Also, the gas holdup in liquid slugs was calculated by using Maxwell equation. On that basis, the gas holdup series was simulated at different spacing between valves based on the gas slug ratio in pipe. By analyzing the fluctuation of gas holdup series, the floor level of trapping times was indicated under the condition of 95% confidence coefficient and 5% permissible error at different spacing between valves. Finally, an experiment was conducted to assess the trapping times in QCV with the spacing setting at 1.55 m length. The measuring errors of gas holdup using QCV method was statistically analyzed, and it was proved that the design guideline provided a sufficient condition for setting up the spacing between valves.

Key words: gas-liquid two-phase flow, slug flow, gas holdup, QCV method

摘要：

快关阀法(quick closing valve,QCV)是气液两相流流动实验中常用持气率标定手段。特别是由于段塞流中气塞与液塞表现为随机可变流动特性,不合理的快关阀间距及截取次数选择将会导致持气率测量误差增大。提出了一种持气率快关阀法优化设计方案。首先,采用环形电导传感器上下游阵列信号计算流体相关流速,根据相关测速结果提取上游传感器信号对应流动工况的气塞与液塞间隔长度序列,采用Maxwell方程提取液塞中含泡持气率;在此基础上,再依气塞在管道内占比模拟计算不同快关阀间距时捕获的持气率波动序列。通过分析持气率序列波动,从统计学角度指出了95%置信度及5%允许误差情况下所需最低截取次数。最后,在快关阀门间距为1.55 m的条件下对段塞流所需截取次数进行了实验验证。通过对快关阀法持气率测量误差进行统计分析,证明了设置两个快关阀门间距的充分条件。

关键词: 气液两相流, 段塞流, 持气率, 快关阀法