Differential-pressure flow meters (orifice plates, Venturi tubes, flow nozzles, dall tubes) measure volumetric flow by placing a restriction in a pipe and applying Bernoulli's equation and conservation of mass to relate the pressure drop across the restriction to flow velocity, giving a theoretical flow rate proportional to the square root of the differential pressure. This theoretical relation is corrected by an empirically determined discharge coefficient (a function of Reynolds number and the diameter ratio, beta) to account for real, non-ideal, non-frictionless flow. The concept belongs to flow-measurement theory within industrial instrumentation, sitting alongside variable-area, positive-displacement, and electromagnetic/ultrasonic flow-sensing principles as one of the constricted-flow methods for determining volumetric or mass flow of process fluids.
Differential-pressure flow meters (orifice plates, Venturi tubes, flow nozzles, dall tubes) measure volumetric flow by placing a restriction in a pipe and applying Bernoulli's equation and conservati…