Designing and teaching application of an experimental platform for a droplet impacting on a heated surface

The phenomenon of a droplet impacting a heated surface is widely used in a number of important fields, such as spray cooling, desalination, agricultural irrigation, and fire-fighting. However, the phenomenon of a droplet impacting a heated surface is very complex and involves the combined knowledge of several disciplines, such as engineering thermodynamics, heat transfer, and fluid mechanics. In addition, the phenomenon of a droplet impacting a heated surface is affected by a variety of factors, such as surface characteristics, droplet properties, and environmental conditions. Therefore, studying the impact pattern and dynamic characteristics of a droplet on a heated surface is of great importance.

To strengthen the understanding and mastery of students on the phenomenon of a droplet impacting a heated surface, an innovative teaching model combining experimental operations and course design is proposed. First, an experimental platform for the droplet impacting on the heated surface is constructed by arranging and adjusting the following: a high-speed camera, an automatic injection system, an intelligent constant temperature heating platform, a digital recorder, a computer, and light-emitting diode background light. Subsequently, deionized water is selected as the experimental droplet, and a 310S stainless steel plate is used as the experimental surface. Furthermore, by adjusting the experimental conditions, such as the droplet falling height and the surface temperature, the experiments of the droplet impacting on the surface are sequentially completed, and the dynamic process and real-time data of the droplet impact on the surface are recorded. Finally, an in-depth discussion about the application of integrating laboratory operations with course design in teaching practice is conducted.

The pattern phase map of the droplet impact on the surface is plotted in detail for the experimental conditions. The pattern of a droplet impacting a surface depends on the surface temperature and the dimensionless Weber number. The impact patterns are classified into four types at different heights and surface temperatures, which are adhesion, rebound, rebound-breakup, and breakup patterns. The dynamic parameters of the droplet were intensively investigated with different heights and temperatures. When the surface temperature is constant, the spreading diameter of the droplet considerably increases with the increase in the impact height. When the impact height is constant, the spreading diameter of the droplet increases and then decreases with the increase in surface temperature.

By carrying out the experimental research on a droplet impact on a heated surface, the students deepened their understanding of the theoretical knowledge, the experimental impact phenomenon, and the variation rule of the dynamic parameters of a droplet impact on a heated surface. In addition, a laboratory lesson was developed and designed based on eight aspects: course objectives, course essentials, experimental process for students, experimental techniques, teaching methods, experimental risks, protective measures, and assessment and feedback, which improved the participation and problem-solving ability of students. The satisfaction of the students with the course was surveyed based on five dimensions: completion of experimental techniques, advanced experimental equipment, interactive course design, diversity of teaching methods, and feedback on teaching quality. The survey results found that the satisfaction levels among students with the experimental courses were all more than 90%. Positive feedback from students not only validates the effectiveness of the experimental teaching methodology but also provides guidance for the continued optimization of teaching methods and course content.