In LNG shipping / offshore offloading, liquid motion within the container sometimes leads to vapor entrapment at the container walls. Dynamic behavior of the entrapped vapor is governed by its thermal or thermodynamic state and profoundly affects LNG sloshing pressure on the container walls. In this paper, the authors will discuss experimental observation of condensable vapor dynamics including steam and natural gas at cryogenic temperatures. Additionally, the authors will also discuss relevant implications in sloshing experiments and the scale up to prototype design.

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Situations involving liquid impact on solid surfaces represent a class of mechanics that has broad practical application. In addition to the liquid and solid surface, most real applications occur in the presence of a vapor. This multiphase physics is complex, and the ambient vapor can have a major influence on the maximum impact pressure. While the ambient vapor is often ignored for its relatively low density, the experimental data in this paper illustrate that ambient vapor/liquid properties and their interaction during an impact event can alter maximum pressures by as much as 2 orders of magnitude. These experiments also provide a basis to demonstrate that the effect corresponds well to a dimensionless "Interaction Index" proposed in this paper. This index is a function of the ambient vapor and liquid properties that account for the degree of influence on the resulting pressure time history. The Interaction Index also provides an essential building block for scaling of experiments. The paper includes both a mathematical formulation and relevant physical test data. The results show that the Interaction Index performs remarkably well in physical tests over a broad range of vapor properties.

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