Averaging Pitot Tube Pdf Printer
A pitot tube can be used to measure fluid flow velocity by converting the kinetic energy in a fluid flow to potential energy. The principle is based on where each term of the equation can be interpreted as pressure p + 1/2 ρ v 2 + γ h = constant along a streamline (1) where p = (relative to the moving fluid) (Pa) ρ = (kg/m 3) v = flow velocity (m/s) γ = ρ g = (N/m 3) g = (m/s 2) h = elevation height (m) Each term of the equation has the dimension force per unit area N/m 2 (Pa) - or in imperial units lb/ft 2 (psi). Static Pressure The first term - p - is the static pressure. It is static relative to the moving fluid and can be measured through a flat opening in parallel to the flow. Dynamic Pressure The second term - 1/2 ρ v 2 - is called the dynamic pressure.
Hydrostatic Pressure The third term - γ h - is called the hydrostatic pressure. It represent the pressure due to change in elevation. Stagnation Pressure Since the Bernoulli Equation states that the energy along a streamline is constant, (1) can be modified to p 1 + 1/2 ρ v 1 2 + γ h 1 = p 2 + 1/2 ρ v 2 2 + γ h 2 = constant along the streamline (2) where suffix 1 is a point in the free flow upstream suffix 2 is the stagnation point where the velocity in the flow is zero Flow Velocity In a measuring point we regard the hydrostatic pressure as a constant where h 1 = h 2 - and this part can be eliminated. Since v 2 is zero, (2) can be modified to: p 1 + 1/2 ρ v 1 2 = p 2 (3) or v 1 = 2 (p 2 - p 1) / ρ 1/2 (4) where p 2 - p 1 = dp (differential 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 dp = p 2 - p 1 and the density of the fluid. It is common to use. (4) can be modified to v 1 = c 2 g (h 2 - h 1) 1/2 (5) where c = coefficient g = acceleration of gravity (m/s 2) h 2 - h 1 = height difference (m) The Pitot Tube The pitot tube is a simple and convenient instrument to measure the difference between static, total and dynamic pressure (or head). The head - h - (or pressure difference - dp) can be measured and calculated with, electronic pressure transmitters or similar instrumentation.
Air Flow - Velocity and Dynamic Head Chart The charts below are based on air density 1.205 kg/m 3 and water density 1000 kg/m 3. Note that as indicated in the diagram above - pitot tubes are not suited for low velocity flow. Due to low dynamic pressure (head) the readings will be inaccurate. Water Flow - Velocity and Dynamic Head Chart.
Averaging Pitot Tube Pdf Printers
Point Velocity Area Method for Flow Metering The point velocities in a duct, channel or pipe can be measured by traversing the cross-sectional area of the conduit. The point velocities can be used to calculate the average velocity that can be used to estimate the flow. The average velocity cab be calculated as v a = Σ v n / n = (2 g Σ h n / n ) 1/2 (6) where v a = average velocity (m/s, ft/s) v n = point velocity (m/s, ft/s) h n = point height difference pitot meter (m, ft) n = number of point velocities The volume flow in the conduit can be calculated as q = v a A (7) where q = flow (m 3/s, ft 3/s) A = cross-sectional area (m 2, ft 2).
Dwyer Averaging Pitot Tube
Meriam manufactures the widest range of Averaging Pitot Tubes for gases, liquids and steam with bi-directional flow capability. Under the Accutube brand name, there are four standard models; Inline, Insertion, Flanged and Wet Tap which can provide a flow solution for your toughest applications. To provide the complete flow solution that meets your specific needs, we can provide DP or Multivariable transmitters from the brand of your choice, or we will recommend the best fit for your application. These transmitters can be installed on the Accutube and configured to your specific flow requirements here at Meriam by qualified technicians, reducing your expense and time.
How A Pitot Tube Works
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