Flow Characteristics of Two-Phase Slug Flow Passing through Porous Plates and Flow Pattern Conversion

本文研究了垂直管内气液两相流从弹状流到泡状流的流型转换。开发了多级多孔板式转化器。它主要由5块ABS塑料多孔板串联组成，能有效地改变流态，即：例如，在转化器下游一定长度范围内存在泡状流<L_B>，通过对单个大气泡在运动液体中上升的实验，得到了转化器的基本特性。然后，得到了与<L_B>多孔板的数量n之间的关系，并且表明可以通过n=2（2级型转化器）的结果来预测转化器的性能。还进行了实验，以关联的单气泡和两相流的性能。根据这些结果，可以从单气泡通过两段式转化器的结果预测多级式转化器在两相流中的性能。然后，对初步实验选择的三种多孔板进行了实验研究。本文将计算结果<L_B>用<j_g>-<j_l>坐标表示，并根据和找到了最佳选择板的方法<j_g><j_l>，其中<j_g>和<j_l>分别为气液体积通量。这些结果被证明是相关的气体分数<f_g>（在弹状流）和（<j_g>+<j_l>）。由于气体分数被发现是一个重要的因素，时间平均气体分数的分布<f_g>被测量沿着管长度。结果表明，<f_g>在转化器下游的某个区域，气体含量比充分发展的弹状流的气体含量大，并且该区域与泡状区有关<L_B>。

This study concerns the flow pattern conversion from slug flow to bubbly flow in gas-liquid two-phase flow in a vertical tube. Multi-stage porous plate type converter was developed. It mainly consists of five porous plates made of ABS plastics arranged in series in a tube, and is effective to convert the flow pattern, i. e., bubbly flow exists downstream the converter in a certain length <L_B> .Experiments were carried out for single large bubbles rising in moving liquid to obtain the fundamental chracteristics of the converter. Then, the relationship between <L_B> and the number n of the porous plate was obtained, and it was shown that the performance of the converter was possible to be predicted by the results for n=2 (2-stage type converter). Experiments were also carried out to correlate the performances for single bubbles and for two-phase flow. From those results, it is possible to predict the performance of the multi-stage type converter in two-phase flow from the results for single bubble passing through 2-stage type converter.Then, experiments were carried out for three kinds of porous plate chosen by preliminary experiments. The results for <L_B> were expressed in <j_g> - <j_l> coordinates, and method of optimum selection of the plate according to <j_g> and <j_l> was found, where <j_g> and <j_l> are the volumetric fluxes of gas and liquid, respectively. Those results were shown to be related to the gas fraction <f_g> (in the slug flow) and ( <j_g> + <j_l> ).Since the gas fraction was found to be an important factor, distribution of the time averaged gas fraction <f_g> was measured along the tube length. It was found that (i) the gas fraction <f_g> is larger in a certain region downstream the converter than that of fully developed slug flow, and (ii) this region is related to the bubbly region <L_B> .