Physics of boiling liquids
Even moreso than in the established onshore LNG industry, the physical behavior of LNG at the storage and transport conditions plays an important role in the design of offshore (floating) LNG installations and transfer systems. LNG is stored and transported at near to boiling conditions (-161 deg. C and atmospheric pressure). Minimal pressure and temperature fluctuations can cause vapor (bubbles) to develop.
This is of particular relevance in rough bore pipeline systems, where due to the surface roughness local pressure and velocity fluctuations occur near the pipeline wall, a potential cause for bubbles to form.
The interaction between the wall and the boiling liquid at flow conditions is not well understood nor the influence, positive of negative, on the overall flow. Generally it is considered that vapour bubbles have a detrimental effect on flow resistance, yet at the same time studies indicate that the introduction of bubbles underneath the hull of a ship reduce the flow frictional resistance.
Also it should be noted that the above phenomena is not the same as ‘normal’ two-phase flow, where the existence of the two phases is generally dictated by process conditions and static head.
To better understand the fluid-vapor-wall interaction of a liquid in a near to boiling conditions in-depth studying and numerical as well as physical modeling will be required. Fundamental questions are: when do vapor bubbles occur in a liquid near boiling conditions and at which location in a pipe flow what is impact of pipe wall smoothness on vapor bubble occurrence what are the physical properties of the vapor bubbles like: size, distribution, deformability depending on local flow conditions what is impact of vapor bubbles on pipe flow resistance what are the local flow conditions that stimulate vapor bubble implosion