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

研究了垂直管内气液两相流中段塞流向气泡流的流型转换。研制了多级多孔板式转炉。它主要由5块ABS塑料制成的多孔板串联在一根管内组成，可以有效地转换流型，即在转化器下游存在一定长度<L_B>的气泡流。为了获得转化器的基本特性，对运动液体中单个大气泡的上升进行了实验。然后，得到了<L_B>与多孔板数目n之间的关系，表明n=2（2级型转化器）的结果可以预测转化器的性能。还进行了单气泡和两相流性能的对比实验。根据这些结果，可以从单泡通过两级式转化器的结果来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。<L_B>的结果用<j_g> - <j_l>坐标表示，找到了根据<j_g>和<j_l>优化板材的方法，其中<j_g>和<j_l>分别为气体和液体的体积通量。结果表明，这些结果与段塞流中的气体分数<f_g>和<j_g> + <j_l>有关。由于气体分数是一个重要的影响因素，所以测量了时间平均气体分数<f_g>沿管长方向的分布。结果表明：(1)转炉下游某一区域的气相分数<f_g>大于段塞流完全发育时的气相分数<f_g>;(2)该区域与气泡区<L_B>有关。

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> .