Process of Liquid Film Formation from Single Droplet

The process of droplet-wall collision forming a liquid film is commonly observed in various fields, including energy, aerospace, and chemical engineering. This phenomenon is particularly prevalent in the nuclear energy sector, where steam-water separation equipment often sees extensive droplet-wall interactions leading to the formation of liquid films. Despite its significance, research on liquid films remains relatively scarce, particularly in terms of understanding the mechanisms behind droplet-wall collision and subsequent film formation. Previous studies have employed both experimental and simulation methods to explore this phenomenon. However, experimental approaches are often constrained by factors such as material properties and temperature, limiting their applicability. Moreover, microscopic numerical methods for studying liquid films are generally inefficient and struggle to provide quantitative analysis of film velocity and thickness. In this paper, a method for calculating the formation of liquid films from droplet-wall collisions based on the Eulerian wall liquid film model was proposed. The calculation formulas and definitions for liquid film formation from droplets of varying sizes were introduced, and the accuracy of applying the Eulerian wall liquid film model to these calculations was validated. The method was subsequently applied to practical AP1000 conditions to analyze the dynamic process of liquid film formation from droplets of different sizes on surfaces. This includes the evolution of a single droplet on a surface, the evolution after multiple droplets collide with the surface, and the evolution following continuous droplet impacts. The study provides an effective analytical tool for calculating wall liquid films in devices such as steam-water separators. The relative error between the liquid film thickness obtained from simulations using the Eulerian wall liquid film model and the actual liquid film thickness is within 8%, validating the method’s accuracy. Additionally, when the mass flow rate of droplets at the injection node is low, the droplets are directly spread out by the airflow to form a liquid film. Conversely, if the mass flow rate of droplets at the injection node increases, the top of the droplet is initially lifted by the airflow and subsequently spread out to form a liquid film. Maintaining a constant liquid mass flow rate and gas flow velocity, it is observed that larger diameter droplets form thinner liquid films with greater film width upon impact with the wall. Increasing the gas flow velocity results in a reduction in liquid film thickness and an increase in film velocity, while the film width remains primarily proportional to the droplet diameter. Overall, this research enhances the understanding of the droplet-wall collision process and liquid film formation, offering a robust computational tool for designing and optimizing steam-water separation systems and other similar applications across various industries.