LNG-solid impacts with gas cushioning and phase change

Abstract

LNG-solid impacts with gas cushioning and phase change are investigated theoretically in a coupled inviscid liquid and viscous gas regime. Condensation from the gas to the LNG is driven by local increases in the gas pressure above the saturation vapour pressure. This is modelled as a sink term on the kinematic boundary condition at the gas interface. To leading order, the bulk liquid motion is unaffected by condensation, with its evolution governed by the same boundary integral equation used in models of non-volatile gas-cushioned liquid-solid impacts. The proposed model extends the approach used to describe two-dimensional non-volatile gas-cushioned impacts by incorporating phase change and is applied to a range of physically relevant LNGsolid impacts associated with sloshing. As an LNG free-surface approaches touchdown with a solid wall, a gas pressure build-up occurs in the gap separating liquid from solid, which decelerates and deforms the liquid freesurface. This deformation of the free surface may result in gas entrapment. In non-volatile impacts, pockets of trapped gas are associated with oscillatory pressure signals, while previous experiments have shown that these oscillations may be damped by phase change in impacts involving volatile liquids. Compared to impacts with non-volatile liquids, gas condensation is shown to reduce both the impact pressures and the volume of gas trapped. Depending on the impact parameters, the proposed model differentiates between cases where a pocket of trapped gas may or may not be formed. A criterion on the critical normal impact velocity above which gas entrapment is not expected is obtained. This indicates that across a range of length scales that are physically relevant to LNG sloshing, gas entrapment is not expected for impact velocities greater than 0.05 m s −1. Impacts where gas compressibility is important are investigated, as well as impacts into corners of containment tanks with varying angles. The model developed is suitable for the analysis of small and medium-sized LNG-solid impacts, as well as larger-scale sloshing model tests involving impacts of water cushioned by water vapour. The importance of inertia in the gas is identified in larger scale impacts.

Experimental investigation of wave tip variability of impacting waves

“…35,55 Prior to impact, gas cushioning (i.e., the increase in pressure in front of the wave tip) can also result in deformation of the wave tip. 49,56,57 The wave tip deflection is shown to depend on the density ratio and the scale of the experiment. 39,40 However, accurate measurements of the wave tip deflec-143 tion have up to now not been reported.…”

Numerical simulation of wave impacts with interfacial phase change: An isothermal averaged model

“…However, this work should be seen as only a first step towards more realistic models of wave impacts with phase change. The same kind of approximation for the study of wave impacts is used in other state-of-the-art work, such as [23].…”

Slamming Liquid Impact and the Mediating Role of Air

“…Thus, its interface is in a persistent state of thermodynamic phase transition. When the wave of such a liquid impacts on a wall, the entrapped vapour can condense, thereby diminishing the role of entrapped air [274]. The free surface instabilities can be either be intensified or reduced, depending on a number of ambient conditions.…”