Heildarflæði

Heildarflæði is an Icelandic term used in engineering and hydrology to denote the overall or total flow of a fluid through a system or boundary. It can refer to the volumetric flow rate through a cross-section or to the net flow through a network over a given period. In contexts where the flow is described across multiple paths or surfaces, heildarflæði expresses the combined result of those flows.

In fluid dynamics, the volumetric flow rate Q is defined as Q = ∬_S v · n dA, where v is the velocity field and n is the unit normal to the cross-section S. The concept of heildarflæði can be applied to such quantities when considering the entire boundary of interest or when aggregating flows over parallel channels. In systems governed by mass conservation, the mass flow rate ṁ = ρ Q, with ρ the fluid density, is a related quantity frequently discussed alongside heildarflæði.

Applications of the concept occur across civil engineering and environmental disciplines, including river discharge, water supply networks, industrial piping, chemical reactors, and heating, ventilation, and air conditioning systems. The preferred unit for volumetric flow is cubic meters per second (m^3/s); for mass flow, kilograms per second (kg/s).

Notes: The term is common in Icelandic technical writing as a direct translation of “total flow.” In international contexts, equivalent terms—such as total flow, volumetric flow rate, or mass flow rate—are used depending on the specific meaning.