Analysing the results

The graph logQactual versus log∆h is plotted. By comparing this equation of Log

Qact = ½ Log H + Log n, where n =Cd A3 √ 2 g

1−(A3

A1

)2 with the graph plotted,logQactual

is linearly increasing tolog ∆h and the graph obtained is a linear graph. This

proved that the graph plotted is correct. Next, the gradient from the equation is

0.5 while the gradient obtained from the graph is 0.5461. The theoretical

gradient value and the gradient value obtained from the graph are slightly

different. While the y-intercept obtained from the graph is -3.3432. From y-

intercept, we are able to calculate the value for Cdas below:

Log n =logCd A3 √ 2 g

1−(A3

A1

)2 = -3.3432

-3.3432 = Log Cd(7.854 x 10−5 √ 2 (9.81 )

1−( 7.854 x10−5

3.269x 10−4 )2)

Cd=−3.3432

log(7.854 x10−5 √ 2 (9.81 )

1−( 7.854 x 10−5

3.269 x10−4 )2 )

¿

¿

= 0.9672

Average Cd= 1.0247+1.0988+1.0565+1.0793

4

= 1.0648

However, the calculated Cd and average Cd values are slightly different. Thus,

the overall result that we obtained for venturi meter is incorrect. This is due to

some errors made while conducting the experiment and also errors that might

come from the apparatus been used in experiment. This will further discuss in

question (v).

The graph of Qact against h for method D and 1/D and method upstream and downstream is plotted.

Theoritically,

Qact=Cd (aA

A2-a2 )√2g√Δh .. . .. .. . .. . where (aA

A2 -a2 )=meter coefficient,

thus the graph can also be expressed as

Qact =MX+c, m =Cd(aA

A2 -a2 )√2g.

For the D and 1/2D tappings method, the m=1.3539, therefore;

Cd(aA

A2 -a2 )√2g=1.3539

Cd = 1.3539( A2−a2

aA ) = 1.3539 ( 0.000382−0.00012

0.00038∗0.0001√2∗9.81 ) =1.081

For method D and 1/2D, the average coefficient discharged Cd is,

Average Cd= 1.7449+1.7228+1.7813+ ¿3

¿

= 1.750

For method upstream and downstream, the average coefficient discharged Cd is,

Average Cd = 1.3777+1.5856+1.7472

3

= 1.570

The value of both average coefficient discharged Cd for method D and

1/2D and upstream and downstream is different to each other which are 1.750

and 1.570. The different value is can be caused by some errors that done during

the experiment such as the reading of outlet pipe that is not perpendicular to

our eyes. Other error is might be come from the apparatus.

Based on the experimental results, venturi meter have more losses

compared to orifice meter. This venturi meter losses should be low due to

steam line shape of the diffuser however our experimental data deviate from

the fact. From the observation, venturi meter have lower Cd compared to orifice

meter. So, venturi gives less accurate measurement because its coefficient of

discharge, Cd is lower compared to orifice meter.

Based on the experimental results, which flow meter gives more accurate measurement. Briefly explain your choice.

As the results indicate, the most accurate flowmeter reading was the venture meter. The flow rate to theoretical flow rate ratio for average was slightly higher, this shows that the data collected during the experiment was not significantly accurate. The data collected using the orifcee plate meter was having a greater variation than the accurate value, this shows that there were some errors while conducting the experiment.

Errors during in the Experiment

Systematics error like error with the apparatus. The flexible tube have an air buble inside it. Therefore, it will affect the reading of the height of the manometer.The surface of the manometer ruler is not clear. It confius the reader want to read the scale. As a result, the reading was not precise.Human error also one of the errors happen in the experiment. There is limitation in the time response in human, the observer may not start and stop the stopwatch simultaneously when the water level is reaching.

The parallax error can be reduced by putting a white paper behind the ruler to make the water meniscus be seen more clearly Before start the

experiment, we have to ensure that the air bubble in the flexible tube completely null. So it will gave the precise readings.

Make sure the scale of the ruler is in good condition. So the readers would get the precise readings. The rate of flow of water must be in a steady flow for a constant velocity at nozzle.

All the apparatus is made sure in good condition before the experiment start. In order to obtain a more accurate result, some repetition while taking the reading can be done and average value is calculated.

ConclusionThe objective of this experiment was to determine and compared the coefficient of

discharged, Cd for a series of flow measuring devices.

From the experiment, we can conclude that the logarithm value for Qactual is directly

proportional with the increasing logarithm value for ∆h. We also obtain that the experimental

slopes of graphs are seen to be deviate from the theoretical value Cd. From the graph that we

constructed, we can measure the coefficient discharged, Cd by measuring the slope of the Qactual

versus ∆ h. The height of the manometer reading will effects the coefficient discharged, Cd. And

also, Qtheoritical is inversely proportional to coefficient discharge, Cd. so the higher the Qtheoritical, the

lower the Cd.

However, this experiment involved with some errors that will affect the accuracy of the

result, hence, we should take the measurements repeatedly and carefully throughout the

experiment to minimize the error in the experiment.

Appendices1. Cross sectional area = π radius2

= π x 0.012

= 3.14159 x 10-4 m2

2. Flow rate theoretical,

Q th = a√(2g Δh

1-m2 ) = (3.14159 x 10-4)√ 2 x 9.81x 0.397

1−0.0256 = 8.8823 x 10-4 m3/s

3. Diffrences height, ∆h = height 1, h1 – height 2, h2

= 0.481 – 0.084 = 0.397 m

4. Coefficient discharged, Cd = Qactual / Qtheoritical

= 0.2222 / 0.2258 = 0.9841

5. Logarithm Qactual = Log Qact

= Log 0.2222 = -3.6532

6. Logarithm ∆ h = Log ∆ h

= Log 0.397 = -0.4012