Gasfilm

Gasfilm is a term used in physics and engineering to describe a very thin, continuous layer of gas that resides at an interface between two phases, most commonly between a solid surface and a liquid, or between two solids separated by a gas layer. The gas film is typically micrometers or thinner in thickness and can persist under relatively stable external conditions. Its presence can significantly alter interfacial transport processes, including heat transfer, mass transfer, and friction.

Formation and stability: Gas films form when air or another gas becomes entrapped at a surface due to roughness, texture, or immersion, by outgassing of dissolved gas, or through active gas injection in lubrication or cooling schemes. The interface can be stabilized by surface tension and favorable force balances; stability is sensitive to surface roughness, pressure gradients, liquid viscosity, and flow shear.

Applications and effects: In tribology and gas-film lubrication, a gas film can reduce friction and wear between moving parts, as in air bearings and certain microelectromechanical systems. In heat-transfer contexts, the gas layer can insulate and reduce convective heat transfer, or help remove heat in cooling flows such as turbine blade film cooling. Gas films also influence wetting, dewetting, and bubble dynamics in fluids.

Measurement and challenges: Studying gas films uses high-speed videography, optical interferometry, schlieren imaging, and other surface-sensitive techniques. They are often transient and sensitive to vibrations, pressure changes, and dissolving gases, making control and repeatability challenging.

See also: air film, boundary layer, lubrication, cavitation.