Flow Measurement PDF

Flow measurement Principles and dimensions Speed of flow: m/s Mainly scientific use Mass flow rate: kg/s Most important measured quantity Volume flow rate: m3/s Ratio of mass and volume = density ρ. Not constant Fluids = Liquids and gases G...

Flow measurement Principles and dimensions Speed of flow: m/s Mainly scientific use Mass flow rate: kg/s Most important measured quantity Volume flow rate: m3/s Ratio of mass and volume = density ρ. Not constant Fluids = Liquids and gases Gases: ρ = ρ (T,p) Liquids: ρ = ρ (T) Terms used Turn- down: 10:1 Rangeability :ratio of full scale flow to the minimum flow Non- linear output scale with proportional to flow rate squared Square root extractors , in pneumatic and electronic version Output of the Transmitter P Square Root Extractor Flow Loop with Square Root Extractor Cutoff Relay Effect of Process Conditions ◼ Flow measurements are inferential – Measure a pressure drop and infer a flow ◼ Affect by density of the fluid – Temperature – Pressure – Increasing density increases the indicated flow rate Flow Meters ▪ Head types ▪ Area types ▪ Mass ▪ Positive displacement types ▪ Electrical types ▪ Open channel types ▪ Solid material flow metering Flow Meters (a) Obstruction type (differential pressure or variable area) (b) Inferential (turbine type) (c) Electromagnetic (d) Positive displacement (integrating) (e) Fluid dynamic (vortex shedding) (f) Anemometer (g) Ultrasonic and (h) Mass flow mete  Basic Flow Measurement ◼ Bernoulli’s Equation – A statement of energy conservation 1/2 p+ v 2 + gy = constant describe relationship between pressure and velocity of a flow Flow Pattern Flow velocity variations across a pipe Reynolds number(R) V : the average fluid velocity, D :diameter of the pipe,µ Laminar: Reynolds number(R) =