Venturi Flume Experiment

Venturi Flume Experiment VENTURI FLUME EXPERIMENT THEORY A Venture flume is a structure designed to achieve critical flow by constricting the width of the channel. It is used in flow measurements of very large flow rates. At critical flow further reduction in the width of the flume throat wouldn’t lower the depth of flow. Each channel has a characteristic flow at which it can be said to exhibit minimum energy of flow. This type of flow is referred to as critical flow. When flow is made to pass through the critical depth a stable and reliable relationship exists which can be used to determine the flow in a channel. Some of the structures constructed include broad crested weir, venture flume and simplified crump weir etc.

OBJECTIVE To confirm the expression for the discharge through a venture flume

(

Q=cd √ g {2/3( H +

v )} 2g

)

And to obtain values of Cd and n for the two different flumes investigated.

APPARATUS 1. Stop watch 2. Vernier calipers 3. Measuring gauge

METHODOLOGY 9 readings of head and discharge on each of the two channels fitted with venturi contractions of different lengths were taken. Log Q was plotted against log (H+ v2/2g) for each and values of Cd and n calculated and reported. Neither the values of Cd or n were averaged during the experiment.

Fluid Mechanic Lab reports

Venturi Flume Experiment

RESULTS AND ANALYSIS The results acquired were as on the spreadsheet attached. 2

When Log Q was calculated and plotted against log

v 2 g ) for each of the venturi (see the spread ¿

H+

sheet attached) and values of Cd and n calculated, the values below were achieved

[(

2 v2 :Q=c b g H + √ d From the equation 3 2g

Log Q = Log

[

2n b cd √ g 3

]

+ n Log

For case 1,

-1.0843= Log

[

n

2 b cd √ g 3

]

B is the throat width of the flume=3.276, For case 2,

-1.1559= Log

[

2n b cd √ g 3

]

b = 3.39 cm

DISCUSSION

Fluid Mechanic Lab reports

)]

n

[(

2

v H+ 2g

n

)]

Venturi Flume Experiment A straight line was obtained in each of the graphs.

The slope values were obtained as venturi 1 : 1.6238 venturi 2 : 1.5288 These approximately differ from the theoretical expected value of 1.5 by 0.1238 and 0.0288 respectively. These differ from the approximate theoretical value of 0.98 by a small degree. The difference in values may have been as a result of: 1. 2. 3. 4.

Due to operator errors such as reading errors and timing errors. Leakage of the venturi flume apparatus. Inconsistency in measuring time and volume of discharge. Error of parallax.

CONCLUSION The value of n and Cd were determine hence confirming the expression under scrutiny

2 v Q=C √ g { ( H + )} 3 2g

(

)

REFERENCES Janusz M. Gasiorek, FM Douglas, Fluid Mechanics, 5th Edition, Prentice Hall, 2006

Fluid Mechanic Lab reports