Solid-liquid impact in thermal equilibrium
Ellis Fan is a PhD student in the department Physics of Fluids. (Co)Promotors are prof.dr. R.M. van der Meer and prof.dr. D. Lohse from the faculty Science & Technology from the University of Twente.
Dynamics of solid-liquid impact in thermal equilibrium differ significantly from those in ambient air, primarily due to phase change that can occur during the process. This is particularly relevant for the transportation of cryogenic fuel, such as liquefied natural gas (LNG). Cryogenic fuels are usually transported at atmospheric or increased pressure, such that they are always close to thermodynamic equilibrium with their vapour phase in the containment tanks. Impact of the fuel on the containment wall during transportation, commonly known as sloshing, may induce a sudden high impact load and jeopardise the integrity of the tank. Despite its importance, the sloshing dynamics at thermal equilibrium remain poorly understood due to the lack of fundamental knowledge on the physics of impact phenomena with phase change.
Therefore, in this Thesis, we experimentally investigate the solid-liquid impact dynamics in thermal equilibrium with the setup introduced in Chapter 1 to gain insight into the physics of impact phenomena involving phase change. For brevity, we name such a system in which the liquid is in thermal equilibrium exclusively with its vapour a boiling liquid system.
In Chapter 2, by impacting a circular flat disc on a boiling liquid, we investigate the influence of phase change on the maximum local impact pressure exerted on the disc. We highlight the crucial role of phase change, specifically condensation, in accelerating the vapour pocket collapse, which results in significantly higher local impact pressures compared to what is predicted for an incompressible impact.
Moving into Chapter 3, we look in depth into the dynamics of the entrapped vapour pocket under the circular flat disc upon impact and conclude that the behaviour of the entrapped vapour pocket is dominated by the effect of phase change. Condensation accelerates its collapse while vaporisation is effective in resisting the rapid collapse.
By introducing a low amount of vapour bubbles in the liquid bulk in Chapter 4, we found that although the vapour bubbles collapse in the liquid bulk upon impact, the presence of vapour bubbles in the liquid may reduce the intensity of impact loads under specific conditions.
Finally, in Chapter 5, we employed circular discs with radially symmetric sinusoidal wave structures of different wavelengths to study how the wave structures on the disc dictates the growth of the instability at the water-air interface and the impact load during impact in ambient air condition. Wave structure on the disc affects the amount of air being entrapped and the wetting rate of the surface, effectively reducing the maximum impact force generated upon impact.
Projecting our findings onto sloshing in cryogenic fuel carriers, the study on the impact of discs with wave structure provides insights into the sloshing impact in cryogenic fuel carriers as the inner wall of the tank is usually corrugated to accommodate thermal contraction and to improve impact resistance. Our study reveals the fundamental mechanism by which phase change can cause significant and often detrimental damage during solid-liquid impact in thermal equilibrium. Condensation accelerates the collapse of the vapour and induces large localised impact pressure. Towards the development of an accurate sloshing load prediction model for safe cryogenic fuels transportation, efforts will be required to properly scale up the effects, as sloshing involves a larger mass of vapour, liquid and solid surfaces.
