Effect of gas-liquid two-phase macro-mixing on the uniformity of temperature distribution in a top-blown stirred tank using image analysis

Abstract

This paper investigates the effect of two-phase mixing of gas and liquid in a top-blowing mixing tank on the uniformity of temperature distribution, using hot heat transfer oil and air as the working medium. Results show that temperature difference is the main factor influencing the temperature field uniformity in the mixing tank, and the uniformity of the temperature distribution increases with the temperature difference increased, while the increase of the air flow and the insertion depth of the gun has less influence on the uniformity of the temperature distribution. In addition, a new threshold selection method is proposed for grayscale maps with temperature fields corresponding to different color gradations, in which the overall mean is replaced by the mean of the grayscale values in the target region, and a highly correlated model between the temperature field and the grayscale map is determined with a correlation coefficient of 0.98. Using a thermal imaging camera and digital image processing techniques, combining with a deviation approach, a relative ratio η between the uniformity of the two-dimensional temperature field distribution and the uniformity of the pixel distribution of its corresponding grayscale map is established. In particular, the indicator shows an interesting trend with an increasing temperature difference, i.e., the ratio is close to 1. The effect of bubble-flow topology on the uniformity of temperature distribution was explored, and it was found that betti numbers averages were negatively correlated with temperature distribution uniformity factor. Finally, a correlation model (correlation coefficient of 0.95) between the uniformity of the temperature field distribution and the average volumetric thermal coefficient was obtained experimentally.