Analysis of Different Initial Droplet Parameters on the Motion Behavior of Multi Droplets
Authors: Liu Zhanwei , He Wen , Li Yanlin , Sun Zhiyuan , Bo Hanliang 
Published: November 2024

Accurate and efficient simulation of gas-liquid two-phase flow is not only pivotal in the broader context of energy, chemical engineering, and environmental studies but is particularly crucial in the intricate realm of nuclear energy. Specifically, in nuclear energy systems, vapor separation processes within steam generators exhibit highly complex gas-liquid two-phase flow phenomena. The liquid droplets generated in these steam generators showcase a broad spectrum of velocity, droplet diameter, and angle parameters. This complexity necessitates a meticulous modeling approach to capture the nuanced motion of droplets within a specific parameter range. Despite the critical importance of this task, rationalizing the range of parameters for characteristic droplets remains an underexplored challenge within the domain.

Conventional methods in the study of gas-liquid two-phase flow often resort to employing evenly spaced parameters for droplet selection, and there is no unified quantitative description of the spacing, so the number of droplets is usually too large or too small, which makes the number of divided droplets too small or too many. This predicament results in compromised precision or an unsustainable computational burden. Consequently, there is an urgent imperative to devise a method that not only quantifies but also effectively spaces droplet parameters. Such a method would streamline the selection of characteristic droplet parameters, ensuring precision while minimizing the number of droplet groups to alleviate the computational load.

To address this pressing challenge, our paper introduces a new method for quantitative selection of droplet characterization parameters based on an error criterion. Here the error in the error criterion refers to the magnitude of change in the dependent variable y, such as the exit velocity, after the independent variable x, such as the droplet particle size, has changed compared to a standard value. Therefore, if the variation range of the dependent variable y is small, the number of characteristic droplets can be reduced at this time, and conversely, if the variation range of the dependent variable y is large, the number of characteristic droplets needs to be increased. Meanwhile, the paper systematically analyzes the influence of three key parameters — velocity, angle and radius — on the calculation results and focuses on determining the radius as the main parameter to be considered. Four criteria for the radius are presented and the corresponding formulas are carefully fitted, revealing the two main criteria that are crucial in the selection process. Subsequently, a method for quantitatively classifying the droplet radius based on error is proposed and the feasibility of the proposed method is rigorously verified.

Furthermore, our investigation into the initial conditions of the droplets reveals that droplet diameter exerts the greatest influence on the results, followed by angle, while velocity has the least impact on the droplet motion state. Notably, large droplets exhibit a higher concentration in the center of the main flow, while the distribution of small droplets tends to be more dispersed.

In conclusion, this paper introduces a pioneering approach to partitioning characteristic droplet parameters, showcasing profound significance for simulation applications in diverse fields related to the movement of particles in flow fields. The proposed method not only enhances the precision of simulations but also contributes substantially to the overall efficiency of computational processes in the study of gas-liquid two-phase flow, particularly in the challenging context of nuclear energy systems.