Flow image distortion correction for two-phase flow in micro/mini pipes

Due to the refraction of the pipe wall, the flow images of gas-liquid two-phase flow in micro-/mini-pipe obtained with visualization method are distorted, which fail to reflect the flow information accurately. The present paper investigates the image distortion under several common conditions through light path and simulation analysis. The results indicate that the images obtained with visualization method are linearly enlarged compared with the real structure, and the magnification ratio increases linearly with the increase of refractive index of the liquid phase. The influences of the inner diameter, wall thickness and refractive index of the pipe are relatively small. The magnification ratio is in the range between 1.30 and 1.44 under normal circumstances. Practical void fraction measurement experiments in millimeter-scale pipes were carried out. With the image distortion correction method, the maximum absolute error of the measurement results is decreased significantly (the decrements for the pipes with inner diameters of 2.06, 4.14 and 4.22 mm are 5.46%, 4.66% and 5.16%, respectively), which verifies the effectiveness of this correction method. This study reveals the important influence factors of image distortion, which is of great important significance for accurately obtaining the flow information of gas-liquid two-phase flow in micro-/mini-pipes. © 2020, Science Press. All right reserved.