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In this paper, image processing techniques are employed to investigate the growth and detachment characteristics of initial bubbles in vertical glass tubes. The study explores the effects of different continuous phases (water and Therminol®66), nozzle diameters, air flow rates, and continuous phase liquid levels on the detachment diameter and shape of bubbles. Furthermore, based on the detachment characteristics obtained under various experimental conditions, a novel predictive model for bubble detachment diameter is established in both water and Therminol®66. The results show that the bubble detachment diameter in the continuous phase therminol® 66 is larger than the bubble detachment diameter in water, and that the shape of the bubbles in therminol® 66 is close to spherical, with an ellipsoidal shape in water. With the increase in nozzle diameter and airflow, the bubble detachment diameter increases, and the shape is stretched in the vertical direction. With the increase in the continuous phase liquid level, the bubble detachment diameter decreases, and the shape change is not significant. In addition, the accuracy of the bubble detachment diameter prediction model was validated through experimental data. Compared with the experimental values, the average absolute errors were 5.04% and 5.11% in water and Therminol®66, respectively. This study aims to investigate the characteristics of initial bubble growth and detachment, providing valuable references for nozzle design. [Display omitted] • The growth characteristics of initial bubbles under different working fluids are studied • The shape and diameter of the bubble detachment process are studied under different operating conditions. • A new bubble detachment diameter prediction model is established [ABSTRACT FROM AUTHOR]

In cooling towers and condensers, accurate measurement of the void fraction in gas-liquid two-phase flow can help optimize heat transfer efficiency. By monitoring the void fraction, operational parameters can be adjusted to maximize heat exchange effectiveness. As such, the development of a technique for measuring void fraction in high-temperature and opaque containers is necessary. This paper presents a method for measuring the void fraction of the section during direct contact heat transfer using electromagnetic tomography. In order to enhance the magnetic field, a certain amount of nanofluid is introduced into the direct contact evaporator. With the aid of a self-developed EMT system, the gas and liquid phases are differentiated, ultimately yielding the section void fraction value. The final results are qualitatively consistent with three classical models for void fraction calculation. This is the first report on measuring cross-sectional void fraction in direct contact heat transfer processes using the EMT system. The findings demonstrate the feasibility of the measurement method based on EMT and provide a reference for research on high-precision and automated measurement techniques of void fraction in gas-liquid two-phase flow. [Display omitted] • The EMT technique is suitable for flow pattern detection of direct contact heat transfer processes. • The void fraction rate of EMT data has the highest correlation with the drift flow model trend. • The void fraction measured by EMT method has a consistent trend with the results calculated by three classic models. [ABSTRACT FROM AUTHOR]