Upward two-phase flow in two different vertical narrow gaps was investigated experimentally. For better understanding the characteristics of air-water flow in rectangular channels, the visual images were captured through high-speed cameras and the void fraction results were obtained through three impedance void meters. The flow pattern was identified through ReliefF-FCM clustering algorithm to avoid the subjectivity of human observation. The flow regime maps were plotted in two different forms, superficial velocities and void fraction and compared with the previous model in the open literature. Through the analysis of the experimental results, the air-water flow in narrow rectangular channels is characterized by the limitation of bubble distribution, coalescence and movement. The probability of bubble coalescence in narrow rectangular channels is increased compared with those in conventional channels due to the restriction of the narrower side walls. New transition criteria was obtained according to the drift-flux model and the force balance analysis which shows satisfactory agreements with existing experimental data for gaps of 1–6 mm.

实验研究了在两个不同的垂直窄间隙中的向上两相流动。为了更好地理解矩形通道中空气-水的流动特性，通过高速摄像机捕获了视觉图像，并通过三个阻抗式空隙计获得了空隙率结果。通过ReliefF-FCM聚类算法确定了流型，避免了人类观察的主观性。流动状态图以两种不同的形式绘制，即表观速度和空隙率，并与公开文献中的先前模型进行了比较。通过对实验结果的分析，在狭窄矩形通道中的空气-水流具有气泡分布，聚结和运动受限的特点。由于窄壁的限制，与常规通道相比，在窄矩形通道中气泡聚结的可能性增加了。根据漂移-通量模型和力平衡分析获得了新的过渡标准，显示出与现有实验数据（1-6mm间隙）的令人满意的一致性。