drainoff

Drainoff (also written drain-off or drain off) is a general term used in several industries to describe the removal of liquid from a material, container, or system. The process typically relies on gravity or suction to withdraw liquid, often while solids remain behind or while the liquid is being separated from a suspension.

Common applications include coating and paint manufacture, where after applying a liquid coating, excess solvent or vehicle is allowed to drain off to achieve a desired film thickness and to improve leveling. In filtration and separation, the liquid portion drains through a porous medium or filter, separating it from solids. In food processing, liquids are drained from solids, such as whey drained from curd or water drained from vegetables. In composite and textile processing, resin or other liquids can drain off from a pad or mat before curing or drying.

Key factors influencing drainoff include liquid viscosity and density, surface tension, temperature, the geometry and orientation of the object, porosity and permeability of the medium, and the presence of drains or channels. Drainoff rates are often described using flux concepts or drainage rate, with units such as liters per square meter per hour in industrial settings or liters per minute for smaller-scale processes.

Quality and safety considerations: improper drainoff can lead to defects such as coating runs or sag, textural inconsistencies in foods, or incomplete separation in filtration. In manufacturing, controlled drainoff is part of process optimization to ensure consistent film thickness, product yield, and overall efficiency.

See also: Decanting, Filtration, Drainage (geology), Drip loss, Draining.