Reference no: EM132313714
Engineering Physics Assignment - Fluids pracs
Write report by follow the instruction and calculate the value given in excel file.
1. Open Channel
Experiment 1: Watch the video.
The channel breadth B = 75mm wide.
Flow is from left to right always.
(These are just reflected lights, not UFOs or anything to do with the prac)
The Weir (the black thing) was used as a flow meter. What you can see is an air pocket at iuts trailing edge.
The flow rate is easy to calculate by using
Q = Cd 2/3 B√(2g) h3/2
Most texts cite Cd (coefficient of discharge) as 0.6 however for this particular piece of equipment Cd = 0.8
And h is the height from the top edge of the weir to the water surface immediately above.
I ran this and measured height, which is in the relevant excel file.
THERE IS ONLY ONE FLOW RATE
Please don't get the idea that the flow rate is different in different places. Yes, the velocity changes, but since over the length of the channel there is nothing extra added or lost, the flow rate is the same everywhere. (Conservation of mass).
I have used this wing shaped thing, which we will call "the object". It is 150mm long, 75mm wide (full width of the channel) and 25mm at its "thickest".
For a frame of reference I have called the front edge of the object (LHS) 0. Upstream, to the left is negative, downstream is positive.
The pump was turned back on, with the same flow rate as before. (The flow rate is controlled by a valve, tuning the pump off and on does not alter the valve setting).
The dynamic head from the pitot tube was recorded at various locations. These are on the results excel file. This shows measurement taken at x = 90mm.
At the SAME locations as the dynamic head I have measured static head, from the water surface to the channel floor either side of the object; and from surface to top side of object in the case of 0 < x < 150mm. These are also on the results excel file.
YOUR TASK:
At all data points you can do 2 things:
With dynamic head use Bernoulli to determine the flow velocity at each point. The height of water in the pitot tube relates toi velocity.
Since static head is also known at these points, and since the B of the channel is constant (75mm) you know the area of the flow. Use Continuity to determine the mean velocity. u = Q/A.
Compare velocities from each method.
The sum of Pressure head + dynamic head + static head should be conserved at all points (within reason). Is it?
Experiment 2: Open Channel Flow Practical
This practical will be carried out with the equipment set at one flow rate only. This will be selected randomly. The selected equipment provided includes the rectangular notch weir. This is used as a flow measurement device. With this placed in the channel, the flow rate can easily be measured from the measured height of the water over the weir, and knowing that the coefficient of discharge of that device is 0.8. With the weir removed, the group will select an obstruction to place in the channel. The dimensions of this object might be relevant. Restarting the pump will cause flow over the object. The important point to remember is the flow rate is the SAME everywhere in the channel: upstream, over the obstruction, downstream. It does not change. What does change is pressure, velocity, and static height of the fluid. This is what you need to compare, not flow rates. Velocity can be measured using the Pitot tube. Static head can be measured using the verniers. What you need to determine is whether at selected locations before, over and after the obstruction that energy in the form of pressure, kinetic and potential can be accounted for. For this you will need to use Continuity equation and Bernoulli's equation. Submission requirements - A concise, well-written report based on the structure detailed in "report writing". - Your description of the experimental method should be original, not simply what is written in this document - A labelled schematic diagram is required for identifying key features. A photo is not a diagram. - Calculations need to be clearly laid out and easy to follow. - Plots of P, u, y, as a function of location along the channel might be useful. In Excel use x-y scatter. - Do not include spurious errors. Quantify the uncertainty of measurement with anything you have measured and quantify how this inaccuracy affects the calculated result. - Draw the appropriate conclusions.
2. Measurements over object
Distance measurement: 0 is leadig edge of object. + is downstream of this Staztic head is depth from water surface, to channel bottom for distance <0 or > 150mm, or to the object top surface for 0 < dist < 150mm.
|
Distance
|
Pitot tube
|
Static head
|
|
mm
|
mm
|
mm
|
|
upstream
|
-1000
|
11
|
65
|
|
-200
|
11
|
71
|
|
-100
|
9
|
73
|
|
Leading edge
|
0
|
12
|
71
|
|
30
|
16
|
48
|
|
60
|
25
|
38
|
|
90
|
31
|
31
|
|
120
|
41
|
29
|
|
trailing edge
|
150
|
48
|
27
|
|
300
|
63
|
22
|
|
600
|
59
|
24
|
|
downstream
|
1500
|
53
|
26
|
Attachment:- Assignment File.rar