## Flow Measurement

Published in: Physics
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• ### Gaurav

• Kota
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• Qualification: B.Tech.
• Teaches: Physics, Mathematics
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Orifice Meter and Venturi Meter

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Flow Measurement (Orifice meter)
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Venturi Service: Clean Liquids, Gases Steam Slurries and Dirty Fluids Scale: Square Root Accuracy: 1% Full Scale Rangability: 3:1 Permanent Pressure Loss: Low Cost: High
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Venturi Effect The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. The Venturi effect is a jet effect; as with an (air) funnel, or a thumb on a garden hose, the velocity of the fluid increases as the cross sectional area decreases, with the static pressure correspondingly decreasing. 5/6/2015
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Venturi Meter From Bernoulli Equation: 2 —2 2g PA PB=h in theoretical velocity: = CVVB t B,act Upstream pressure tap pa Flow direction Downstream pressure tap Flow dire on C takes into account reduction Flow mass is given by: lh=Cv AB VB t Substituting with know values we have: = 0.962 cvhl/2 Density P Venturi tube
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Flow Nozzle Service: Liquids, Gases, Steam, High Velocity FIOWS Scale: Square Root Accuracy: 1% Full Scale Rangability: 3:1 Permanent Pressure Loss: High Cost: High
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Venturi & Flow Nozzle High Pressure Tap ÅJ Short-Form Venturi Tube B) Universal Venturi C) Flow Nozzle
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Orifice meter ' It may be installed in pipeline with a minimum of trouble and expense
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Orifice Service: Clean Liquids, Gases Steam,(no slurries or corrosive) Scale: Square Root Accuracy: 1% Full Scale Permanent Pressure Loss: High Cost: Low
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Orifice meter Flow Orifice plate to manometer (b) Sketch of orifice installation pipe diarneter
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Orifice From Bernoulli Equation: 2 —2 2g in theoretical velocity: = C v VFt F,act Flow mass is given by: m = CC A Cc takes into account the area contraction: cc CD takes into account reduction CD = CCCV Substituting with know values we have: m = 1.398 CDhl/2 Meter O' f ferenttai pressure Pressure DO tum Courtesy of Superior Products, Inc. www.orificeplates.com Differential pressure 10
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Variation of K with Re ' At high Reynolds number K is essentially constant, but as Reynolds number is lowered, K is also increased ' ICmaxm at 200-600
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Variation of K with Re 0.95 0.90 0.85 0.80 0.75 0.70 0.65 0.60 102 2 5 103 0.50 0.30 5 107 2 Reynolds number of approach,
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Variation of K with Re (cont) The lowering of Reynolds number increases viscous action which causes a decrease in cv and an increase in C The latter apparently predominates over the former until Cc reaches its maximum value (about to 1) With further decrease in Re, 'K' then becomes smaller because cv continues to decrease
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Orifice meter ' Disadvantage Its practical disadvantage is that- it offers greater frictional resistances as compared to

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