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Flow Through a Model Venturi Meter.

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FLOW THROUGH A MODEL VENTURI METER OBJECT: * To determine the coefficient of discharge of meter and its variation with discharge. * To determine the variation of energy loss through the meter as a function of discharge and main pipe velocity. Introduction: A venturi meter is a tube with a constricted throat that increases velocity and decreases pressure. They are used for measuring the flowrate of compressible and incompressible fluids in pipeline. APPARATUS AND THEORY: A venture meter is essentially a convergent-divergent constriction in a pipeline. The change in pressure in the fluid as it passes through the meter can be used to determine the flowrate. Continuity equation: V1A1 = V2A2 = V3A3 (1) Bernoulli equation: + h1 +Z1 = + h2 +Z2 = + h3 + Z3 (2) Consider the upstream section (=1) and the throat section (=2) from equation (1) V1= and the substituting this into equation (2) with Z constant and taking (a) = (b) then V2 = [1 - (A2/A1)2]-1/2 * (3) Where (h1-h2) is the deference in the levels in manometer limbs 1 and 2 Now apply continuity equation (1) ...read more.


For a series of different flow rates Q, piezmeter levels h1, h2 h3 and the actual flowrate was recorded. Flow was altered by adjusting the valve downstream of the meter- steps of 20mm rise in the h2(throat) reading are usually suitable until the value of (h1-h2) was about 60 mm ,then raise h2 in steps of about 10mm or 5mm until (h1-h2) is nearly zero. Run No. h1 h2 h3 h1-h2 h1-h3 t1 t2 T (h1-h2)^.5 1/time 1 0.241 0.002 0.203 0.239 0.038 16.36 16.4 16.38 0.488876262 0.061050061 2 0.21 0 0.177 0.21 0.033 17.62 17.77 17.695 0.458257569 0.056513139 3 0.206 0.02 0.175 0.186 0.031 19.04 18.45 18.745 0.431277173 0.053347559 4 0.203 0.054 0.175 0.149 0.028 20.09 20.01 20.05 0.386005181 0.049875312 5 0.198 0.062 0.174 0.136 0.024 21.95 21.89 21.92 0.368781778 0.045620438 6 0.197 0.071 0.174 0.126 0.023 22.81 22.72 22.765 0.354964787 0.043927081 7 0.19 0.106 0.173 0.084 0.017 27.25 27.02 27.135 0.289827535 0.036852773 8 0.186 0.121 0.172 0.065 0.014 32.86 32.2 32.53 0.254950976 0.030740855 9 0.182 0.141 0.173 0.041 0.009 41.09 40.81 40.95 0.202484567 0.024420024 10 0.18 0.161 0.175 0.019 0.005 60.31 60.23 60.27 0.137840488 0.016592003 11 0.179 0.17 0.177 0.009 0.002 85.09 85.21 85.15 0.09486833 0.011743981 RESULT: Experimental results: Table (1) ...read more.


In order to account for this difference, a discharge coefficient Cd is introduced into the flow equation. Cd is not constant because it depends on the Reynolds Number and the ratio of nozzle to pipe diameter. 2) What are the sources of energy loss in the meter? * Friction that caused by turbulence flow inside the meter * Pressure effects. 3) When velocity is increase the pressure will decrease, and that will reduce the pressure effect which it source of energy loss, it will be a constant and vaule will be between 0.5 and 1. When I compared the graphs which I got with the lab sheet graphs I found that: Graph (1): the graph was similar to the one in the lab sheet. Graph (2): the graph was completely different to the lab sheets graph, that difference can be happened because of the accuracy of the reading. Graph (3): the graph was slightly different from the one which is in the lab sheet. The values of Cd which I got it was right because it was between 0.95 and 0.99 except two readings. ...read more.

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