flowmeasuring

Flow measuring, or flow metering, is the process of determining the rate at which a fluid moves through a pipe, channel, or other conduit. The quantity most commonly reported is volumetric flow rate (Q), in units such as cubic meters per second or liters per minute, or mass flow rate (ṁ), in kilograms per second. Accurate flow measurement supports process control, inventory management, and safety.

Measurement methods are based on underlying physical principles. Differential-pressure meters infer flow from a pressure drop across a constriction, using devices such as orifice plates, venturi tubes, and flow nozzles. Positive-displacement meters measure a fixed volume per cycle and are effective for high-viscosity or low-flow fluids. Velocity-based meters determine flow from fluid velocity, employing turbine, magnetic, ultrasonic, or pitot-type devices. Coriolis meters measure mass flow directly by sensing forces on vibrating tubes, while thermal mass meters infer flow from heat transfer in gases or liquids.

Common device characteristics include simplicity and low cost for orifice plates, lower pressure loss for venturi meters, and the requirement for conductive fluids in magnetic meters. Ultrasonic meters offer clamp-on or inline options and suit a range of liquids; turbine meters provide good accuracy for clean, low-to-moderate viscosity fluids; Coriolis meters deliver high accuracy and direct mass-flow measurement; thermal meters are robust for gases and some liquids.

Open-channel flow uses methods such as weirs and flumes, distinct from closed-pipe flow. Installation considerations—straight runs, fluid properties, temperature, density, and presence of entrained air—affect accuracy and calibration. Flow metering finds use across water and wastewater, oil and gas, chemical processing, food and beverage, HVAC, and pharmaceuticals, with standards guiding calibration and data quality.