flowrate

Flowrate, or flow rate, is the quantity of fluid that passes through a boundary per unit time. It is a fundamental measure in fluid dynamics and is used to describe how much fluid moves in a system such as pipes, channels, or ducts. Flowrate is commonly expressed as volumetric flow rate or mass flow rate.

Volumetric flow rate (Q) is the volume of fluid passing per unit time. It is often written as Q = dV/dt and can also be expressed as Q = A × v̄, where A is the cross-sectional area of the conduit and v̄ is the average fluid velocity. Mass flow rate (ṁ) is the mass of fluid passing per unit time and is related to volumetric flow rate by ṁ = ρ × Q, where ρ is fluid density. For incompressible fluids with constant density, ṁ remains constant along a closed system, as described by the continuity equation.

Common units include volumetric flow rate in cubic meters per second (m^3/s), liters per minute (L/min), or gallons per minute (GPM), and mass flow rate in kilograms per second (kg/s) or pounds per second (lb/s). In gas dynamics, density changes with pressure and temperature, so mass flow rate is often preferred for consistency. Standard or base conditions (e.g., standard temperature and pressure) are used to compare flow rates of gases.

Measurement methods include differential-pressure meters (Venturi, orifice), turbine meters, electromagnetic meters, Coriolis meters, and ultrasonic meters. Choices depend on fluid properties, required accuracy, and the presence of entrained solids or multiphase flow.

Applications span water distribution, chemical processing, oil and gas, HVAC, and biomedical contexts, where precise control or monitoring of flowrate is essential.