Flowmeting

Flowmeting, or flow measurement, is the process of determining the rate at which a fluid moves through a cross section of a pipe or channel. It applies to gases, liquids and steam, and the result is typically a volumetric flow rate or a mass flow rate, expressed in units such as cubic meters per second, liters per second, or kilograms per second.

Flow measurement can be achieved with devices that link flow to an observable variable such as differential pressure, fluid velocity, or mechanical displacement. Major families include differential pressure meters (such as orifice plates, venturi tubes and flow nozzles), positive displacement meters, and velocity meters (including electromagnetic, ultrasonic, turbine, vortex and Coriolis meters). Coriolis meters measure mass flow directly, while differential pressure meters relate flow to a pressure drop across an obstruction.

Differential pressure meters rely on Bernoulli’s principle: a constriction causes a pressure drop that correlates with flow. Orifice plates are simple and inexpensive but introduce relatively large pressure losses; venturi tubes and flow nozzles offer lower pressure loss for the same measurement range. Positive displacement meters measure flow by trapping fixed volumes of fluid and are often used for viscous liquids. Velocity meters determine flow by measuring fluid speed and deriving flow from cross-sectional area; many are suitable for wide ranges and complex fluids.

Installation considerations include upstream and downstream straight runs, fluid properties, temperature and pressure, and proper calibration. Standards and guidelines exist to define accuracy, installation, and uncertainty, with ISO 5167 for differential pressure meters and industry practices in gas and oil applications.

Applications span water supply and wastewater, chemical processing, oil and gas production, food and beverage, and HVAC systems, wherever accurate, reliable flow information is needed for process control, custody transfer, or energy management.