Kaasunsiirto

Kaasunsiirto, or gas transfer, refers to the transport of gas molecules between phases, most commonly between a gas and a liquid, but also across membranes or porous solids. In scientific and engineering contexts it describes the rate at which a gas dissolves into a liquid or is released from it, driven by differences in partial pressure or chemical potential.

In a gas–liquid system the transfer proceeds through resistances in the gas boundary layer and the liquid boundary layer around the gas–liquid interface. The two-film theory and related penetration models describe how these resistances limit the rate. The current, or flux, N is often written as N = k_L a (C* − C_L), where C* is the gas-phase equilibrium concentration (given by Henry's law) and C_L is the actual dissolved concentration. The overall transfer is influenced by temperature, pressure, liquid viscosity, interfacial area, bubble or droplet size, and mixing intensity. Dimensionless numbers such as the Sherwood (Sh), Reynolds (Re), and Schmidt (Sc) help compare systems.

Measurement and design often use the volumetric mass transfer coefficient k_L a as a key figure of merit, with common methods including dynamic gassing-out tests or the sulfite chemical technique in oxygen-transfer studies.

Applications of kaasunsiirto span bioprocessing, where oxygen transfer limits fermentation and cell culture, environmental engineering with aeration and air stripping, chemical engineering in gas absorption and scrubbing, and medical devices that rely on gas exchange. Challenges include low gas solubility, temperature sensitivity, and achieving high interfacial area without excessive energy input.