Läpivirrto

Läpivirrto is a Finnish term used in technical and scientific contexts to denote a process in which a quantity, such as a fluid, heat, or a signal, passes through a system from one boundary to another without being stored or accumulated within the system. The concept is broadly applied to describe pass-through transport or transmission through materials, devices, or landscapes.

In hydrology and soil science, throughflow refers to water moving through soil or sediment from the surface toward drainage outlets, contributing to runoff and affecting infiltration dynamics. In chemical engineering and filtration, throughflow describes the movement of a fluid or gas through a porous medium, catalyst bed, membrane, or reactor, influencing efficiency, residence time, and selectivity. In ecology or environmental science, it can describe the transport of nutrients, contaminants, or heat through substrates or sediments. The exact meaning depends on the disciplinary context and the system being described.

Etymology and usage notes: the term is a compound of läpi "through" and virrto, a root related to virtaus "flow," used in Finnish technical vocabulary to express pass-through behavior. Because Finnish terminology varies by field, läpivirrto may be defined more narrowly in some disciplines and more broadly in others.

See also: throughflow (English terminology), permeation, transmission. The term is primarily found in Finnish-language sources, and translators typically choose the most field-appropriate equivalent in English, such as throughflow, permeation, or flow-through, depending on the context.