Demisters

Demisters are devices designed to remove liquid droplets from gas streams or to prevent condensation on surfaces. In process industries, they are often called mist eliminators or demisting devices and are used to reduce liquid carryover from gas–liquid separations. In HVAC and automotive contexts, a demister or defogger directs warm dry air onto a surface to evaporate and disperse moisture.

In gas–liquid separators, demisters are installed in knockout drums, absorbers, or distillation columns as pads, nets, or vane packs. The mechanism relies on coalescence: fine droplets collide and coalesce on the demister surface to form larger droplets that drain away by gravity, thereby reducing entrainment in the gas stream. The choice of type (mesh/pad, vane, or mesh with drainage) depends on gas velocity, liquid properties, and temperature.

Common applications include natural gas dehydration plants, refinery gas streams, petrochemical absorbers, and distillation columns; they improve product purity and protect downstream equipment by limiting carryover and corrosion from liquids.

In building and automotive use, windshield demisters employ heated or blown air to remove condensation and fogging from glass surfaces. Design considerations include air temperature and distribution, energy use, control mechanisms, and maintenance to prevent fouling of the demister media or vents.