Three-dimensional measurement of bubble in gas-liquid flow by light field photography

A three-dimensional measurement method for bubble parameters in gas-liquid two-phase flow was proposed based on the light field photography for solving the problem that bubble parameters could only be measured in two-dimensional problems using conventional photography. The light field camera recorded the light field information of the gas-liquid two-phase flow, and then the total focus image and the refocused images of the bubbles in the two-phase flow field were obtained using a computational imaging technique. The image processing was performed by binarizing the total focus image to obtain the projection of bubbles in the depth direction and evaluating the sharpness of refocused images to obtain the depth of bubbles. Based on the bubble projection and depth information, the three-dimensional reconstruction of the bubbles was achieved, and the parameters, such as size distribution, spatial position and gas void fraction of bubbles were further calculated. The calibration and the experiment were made to evaluate the proposed method. Experimental results show that the cross-sectional void fraction in the depth direction is in agreement with the bubble depth distribution and oscillates periodically in the vertical direction. With the increase of gas flow rates from 0.5 L/min to 1.1 L/min, the amount of bubbles increases from 28 to 72; the average diameter of bubbles maintains about 1.56 mm before the gas flow rate reaches 0.9 L/min, after increasing sharply; the gas volume fraction rises approximately linearly, and the bubble depth interval increases gradually. The three-dimensional reconstruction results of bubbles are in good agreement with the law of bubble formation and distribution, thus verifying the feasibility of the proposed method.