CE 271 FLUID MECHANICS FLOW THROUGH ORIFICESCONTENT

i. Introductionii. Aim iii. Apparatus usediv. Theoryv. Procedurevi. Data Analysis & Calculationsvii. Discussion

INTRODUCTIONThe analysis of the quantity of water which can be discharged through an orifice is arrived at in a simple, straightforward manner by the application of Bernoulli's equation. However, experimental tests typically produce a result which is only some 65% of the solution indicated by the simple analysis. The study of water flow through an orifice is therefore a classic topic to illustrate the need for a semi-empirical approach which is so often required in Mechanics of Fluids.

LIST OF SYMBOLS

across sectional area of orificem2

accross sectional area at vena contractam2

Cccoefficient of contraction

Cdcoefficient of discharge

Cvcoefficient of velocity

gacceleration due to gravity 981m/s2

hdifference in heightm

volume flow ratem3/sec

xhorizontal distancem

yvertical distancem

RESULTS

According to x versus (4hy)0.5 ,Cv value that we got from the slope of the graph is almost equal to the theoretical values that we calculated from the equation.

DISCUSSIONThere are two methods of analyzing the discharge of a vessel through an orifice. The first of these applies when the orifice is small in comparison with the head above the orifice; this is known as small orifice analysis. In this case variations in velocity with height within the jet of water can be ignored and the velocity is assumed to be constant.The alternative analysis for large orifices takes into account the variation of velocity with height within the jet of water issuing from the orifice.

Many constants were calculated during the experiment

They were,Cd = Coefficient of Discharge =Actual measured discharge/ Theoretical dischargeCc = Coefficient of Contraction =Area of the jet at vena contracta / Area of the orificeCv = Coefficient of Velocity =Velocity at vena contracta / Theoretical Velocity

When we consider Cv values for the 4mm and 6mm, theoretical values that we calculated from the equations are lower than the experimental values. For Cd values theoretical values are higer than the values that we calculated from the equation.

Reasons for variations between theoretical and experimental values are, Human errors Frictional loss in liquid Measurement errors Change in water level Defects in orifices The fluid does not flow in streamline condition. Specially with higher H values.

Methods that could be used to improve this practical When measuring Q, time for a large volume of water so the error caused by measuring the time is minimized. This experiment should carry out for a large no of different H values so that the human and measurement errors are minimized. A see-through bucket should be used when taking the x values The amount of pipe that comes out from the tank should be minimized to lower the frictional loss.

REFERENCES

Mysite.du.edu,fluids/orifice[online], last accessed on 23rd of march 2014 at:http://mysite.du.edu/~jcalvert/tech/fluids/orifice.htm

cee.citadel.edu,fluid lab/theory files[online], last accessed on 23rd of march 2014 at:http://cee.citadel.edu/civl418/Fluids_Lab/Laboratory_Theory_files/Flow%20Through%20Orifices.doc

Wikipedia.org,bernoullis principle[online], last accessed on 23rd of march 2014 at:http://en.wikipedia.org/wiki/Bernoulli's_principle

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