Numerical analysis of Laplace force modification on dro‎plet jumping on microstructure surface

6/3/2026 12:00:00 AM

The phase change of vapor to liquid at constant pressure, condensation, occurs in two ways: Filmwise an‎d dro‎pwise condensation. In dro‎pwise condensation, dro‎plets may slide an‎d separate from the surface or, as they merge, the released energy is converted into kinetic energy, causing them to separate from the surface. The probability of separation an‎d jumping of smaller dro‎plets is greater than that of larger dro‎plets, an‎d their jumping speed is also greater. In the dro‎plet jumping phenomenon, a liquid dro‎p is suddenly an‎d at high speed thrown from a liquid surface to the opposite side. This phenomenon occurs for various reasons, including pressure changes, free surface changes, an‎d surface tension changes.In this thesis, the factors affecting the dro‎plet jumping phenomenon are examined an‎d the energy model an‎d the forces governing it, such as surface tension force, retardation force, an‎d center of gravity force, are rewritten.Since, in previous studies, the Laplace force resulting from the Laplace pressure difference an‎d its equations were not considered in the energy model, the necessary correction was made, an‎d the resulting equations were solved again. an‎d then the effect of this force on the phenomenon of separation an‎d jumping of merged dro‎ps was presented. In this analysis, the results of the effect of various parameters such as the initial volume of dro‎ps before merging, surface slope, pillar length, pillar diameter an‎d height on the jumping of merged dro‎ps are presented. For example, in the case of the slope of the surface for two slopes of 5 an‎d 30 degrees, various analyses were performed, an‎d it was concluded that by increasing the slope of the inclined surface without pillars, the separation an‎d jumping of merged dro‎ps occurs nearly 2 milliseconds faster, which means an 18% improvement in jumping. an‎d this increase in slope for the inclined surface with pillars causes the base radius of the coalescing dro‎p to reach zero in a faster time of nearly 7 milliseconds, which results in a 28% improvement in jumping. Regarding the pillar length, 9 different lengths from 0.5 μm to 8 μm with a slope angle of 30 degrees were analyzed for the inclined surface with pillars, an‎d it was concluded that by increasing the pillar length, it takes a longer time (from 0.5 μm to 8 μm, nearly 9 milliseconds) for the base radius of the coalescing dro‎p to reach zero an‎d separation an‎d jump to occur. By reducing the pillar length from 8 μm to 0.5 μm, the jump occurs 9 milliseconds faster, which allows us to improve the jump by 33% an‎d subsequently the heat transfer.

چگالش قطره اي , پرش قطرات , مدل انرژي , سطوح ميكرو ساختار , نيروي لاپلاس

dro‎plet condensation , dro‎plet jumping , Energy model , Microstructure surfaces , Laplace force

Seyed Sajad Aboutalebi

Mr.Hamid Saffari Natanzi