![]() ![]() Orifice, Nozzle and Venturi Flow Rate Meters - The orifice, nozzle and venturi flow rate meters makes the use of the Bernoulli Equation to calculate fluid flow rate using pressure difference through obstructions in the flow.Kinetic Energy - Energy possessed by an object's motion is kinetic energy.Flowmeter - Accuracy - Introduction to accuracy in flow measurement devices.Energy and Hydraulic Grade Line - The hydraulic grade line and the energy line are graphical presentations of the Bernoulli equation.Dynamic Pressure - Dynamic pressure is the kinetic energy per unit volume of a fluid in movement.Specific Weight and Specific Gravity - An introduction to density, specific weight and specific gravity. Comparing Flowmeters - A limited comparison of flowmeter principles - regarding service, rangeability, pressure loss, typical accuracy, upstream pipe diameters, viscosity and relative costs.California Pipe Flow Metering Method - Calculate the discharge length from the open end of a partially filled horizontal pipe.Bernoulli Equation - Conservation of energy in a non-viscous, incompressible fluid at steady flow.Flow Measurement - Flow metering principles - Orifice, Venturi, Flow Nozzles, Pitot Tubes, Target, Variable Area, Positive Displacement, Turbine, Vortex, Electromagnetic, Ultrasonic Doppler, Ultrasonic Time-of-travel, Mass Coriolis, Mass Thermal, Weir V-notch, Flume Parshall and Sluice Gate flow meters and more.2%, 8%, 15%, 23%, 34%, 66%, 77%, 85%, 92% and 98%įor smaller ducts the the average velocity can be estimated to 81% of centerline velocity.The volume flow in the conduit can be calculated asįor round ducts larger than 10 inches the average velocity can be calculated as the arithmetic middle of a 10 point traverse from inward side wall with distance H n = point height difference pitot meter (m, ft) The average velocity can be calculated as The point velocities can be used to calculate the average velocity that can be used to estimate the flow. The point velocities in a duct, channel or pipe can be measured by traversing the cross-sectional area of the conduit. Water Flow - Velocity and Dynamic Head Chart (pdf)įlow Metering - Point Velocity Area Method.Water Flow - Velocity and Dynamic Head Chart Due to low dynamic pressure (head) the readings will be inaccurate. Note that as indicated in the diagram above - pitot tubes are not suited for low velocity flow. Air Flow - Velocity and Dynamic Head Chart (pdf).The charts below are based on air density 1.205 kg/m 3 and water density 1000 kg/m 3. The head - Δ h - (or pressure difference - Δp) can be measured and calculated with the help of u-tube manometers, electronic pressure transmitters or similar instrumentation.Īir Flow - Velocity and Dynamic Head Chart The pitot tube is a simple and convenient instrument to measure the difference between static, total and dynamic pressure (or head). For other units and reference liquids - like mm Water Column - check Velocity Pressure Head. Note! - in the basic equation the head unit is with reference to the density of the flowing fluid. Δh = h 2 - h 1 = height difference (fluid column) (4) can be modified by dividing with specific weight γ toĬ = coefficient - depending on reference liquid and units used or calculated It is common to use head instead of pressure. With (4) it's possible to calculate the flow velocity in point 1 - the free flow upstream - if we know the differential pressure difference Δp = p 2 - p 1 and the density of the fluid. Since v 2 is zero, (2) can be modified to: In a measuring point we regard the hydrostatic pressure as a constant where h 1 = h 2 - and this part can be eliminated. Suffix 2 is the stagnation point where the velocity in the flow is zero Flow Velocity Suffix 1 is a point in the free flow upstream The Bernoulli Equation states that the energy along a streamline is constant - and can be modified to It represent the pressure due to change in elevation. The third term - γ h - is called the hydrostatic pressure. The second term - 1/2 ρ v 2 - is called the dynamic pressure. It is static relative to the moving fluid and can be measured through a flat opening in parallel to the flow. The first term - p - is the static pressure. P = static pressure (relative to the moving fluid) (Pa)Įach term of the equation has the dimension force per unit area N/m 2 (Pa) - or in imperial units lb/ft 2 (psi). The principle is based on the Bernoulli Equation where each term of the equation can be interpreted as pressure A pitot tube can be used to measure fluid flow velocity by converting the kinetic energy in a fluid flow to potential energy. ![]()
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