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1) A network of channels connects different rainwater reservoirs in rural Thailand

Civil Engineering

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1) A network of channels connects different rainwater reservoirs in rural Thailand.  Rainwater is transported by gravity from one reservoir to another and you have been tasked to design the joint between two channels.  Figure Q1 below shows the connection between two water channels with a square cross section.  Channel 1 transports 3.6 m³/s of water and Channel 2 transports 0.4 m³/s.  They join in a main collector Channel 3, also of a square cross-section, and open to the atmosphere in position 3.  The absolute pressure in Channels 1 and 2 are

?₁ = 160 ??? and , respectively.  The volume of water in the section of the channel joint shown in Figure Q1 is 50 litres.  You need to evaluate the force that the concrete enclosure shown must be able to resist (the force applied on the walls).  A detailed explanation of your workings that includes a diagram of all the forces and distances involved in your calculations is required.

(15 Marks)

 

 

 

 

Figure Q1 – Rainwater collector joint

 

 

 

 

 

 

         

2. You have been tasked to build an eco-friendly reservoir to prevent flooding in a rural area.  The system must discharge automatically without an operator or electricity.  An existing pool with a depth of  will be used.  It is important that it does not overflow, so you have proposed the system shown in the Figure Q2 below to extract water when the level of the tank rises to a given point.  A rectangular channel open to the atmosphere is inserted in the tank with a gate hinged at the top.  A hollow plastic buoy automatically pulls the gate open when the level of the water rises.  The existing buoy weights 25 kg; it comprises of a top cylindrical section of and height ?_?,1 = 1 ?, and a bottom conical section of height .  The buoy will be anchored at a distance

 from the bottom of a rectangular gate with a length ? = 50 ??.  The

gate will rest at versus the horizontal.

You now have to find the correct width of the gate, W, so that the gate will open exactly when the buoy has just been fully submerged and the level of the water in the tank has just reached .  A detailed explanation of your working, including a diagram of all the forces and distances involved in your calculations, is required.

(15 Marks)

 

 

Figure Q2 – Rainwater collector reservoir- Rectangular gate open by a buoy

         

3. One of the farms receiving the rainwater uses a cylinder to mill cereal.  It rotates against a quarter of a stationary cylindrical concrete wall.  A 2 mm gap between the wall and the cylinder is lubricated with a viscous liquid.  The standard operating procedure of the mill is to first apply a torque of 30 N.m to make the cylinder rotate slowly for 10 min, and then, apply a steady operating torque of 61 N.m that should make the cylinder rotate at an optimum 0.1 rpm.  Anytime it rotates slower production stops, but there are no problems if it rotates faster.  Table Q3 (on Page 5 of this examination paper) provides the laboratory rheograms attached to four different lubricants available in the local workshop.  They include consecutive experiments increasing and decreasing ??.  Figure Q3 (on Page 5 of this examination paper) provides the details of the lubricated cylinder rotating against cylindrical wall section.

 

1. 1. Identify the type of fluid each lubricant is.  Provide examples of those fluids and explain how they respond to the application of shear stress and why?  Give an equation to predict the rheology of any Newtonian and/or time independent Non-Newtonian lubricant you have identified in Table Q3.
   2. Which lubricants in table Q3 will allow the cylinder to rotate at the required velocity?  A detailed explanation of the use of each equation and your calculations is required.
   3. Explain what will happen to the rotation of the cylinder if each of these fluids are used and give a recommendation to select the best lubricant(s) for this application.

(15 Marks)

 

 

 

Q3 CONT…/

/Q3 CONT…

Table Q3 – Viscometer analysis.  Lubricants #1 to #5 (also available in an Excel file called “Q3-DATA” - see the instructions page at the top of this examination paper).

 

?? / ?⁻¹            Pa

 

# 1        # 2         # 3         # 4         # 5

0 0.0         0.0         0.0         2500.0 0.0

5 427.0    61.7       310.0    2771.8 543.6

10              670.0    200.5    620.0    2973.2 946.4

20              1051.4 651.3    1240.0 3323.9 1647.8

40              1649.8 2116.2 2480.0 3934.5 2869.1

80              2588.8 6875.6 4960.0 4997.7 4995.3

120            3369.5 13698.3              7440.0 5954.7 6909.3

160            4062.3 22339.0              9920.0 6848.7 8697.4

120            3369.5 13698.3              7440.0 5954.7 5527.5

80              2588.8 6875.6 4960.0 4997.7 3247.0

40              1649.8 2116.2 2480.0 3934.5 1578.0

20              1051.4 651.3    1240.0 3323.9 692.1

10              670.0    200.5    620.0    2973.2 283.9

5 427.0    61.7       310.0    2771.8 108.7

0 0.0         0.0         0.0         2500.0 0.0

 

Figure Q3 – A lubricated cylinder rotating against a cylindrical wall section.

         

4. When the collection pool described in Figure Q2 opens, rainwater flows out of the tank at a rate of 9 kg/s through three consecutive pipe sections depicted in Figure Q4 of different length (L₁ = 50 m, L₂ = 60 m, L₃ = 500 m) and diameter (D₁ = 50.0 cm, D₂ = 6.0 cm, D₃ = 9.0 cm).  A system of manometer lines is used to measure pressure at different locations.  It contains mercury and connects the points A and B with point C where it discharges in a reservoir at atmospheric pressure. 

 

The pressure in point A is 133 kPa gauge, and the differential height between points A, B and C are ( and ).  Sections 1 and 2 are both smooth pipes, and Section 3 is a rough carbon steel collector with a relative roughness ?⁄? = 0.005.  Section 1 undergoes a smooth contraction into Section 2 causing no losses, and Section 2 undergoes an abrupt expansion to Section 3.  You may ignore entrance and discharge minor losses.  The following table Q4 lists the instrumentation located in sections 1, 2 and 3.

 

Table Q4: Pipe elements: valves, bends, and fittings.

Section 1	Section 2	Section 3
No instrumentation	One (1) 90o bend (threaded) Two (2) 180o return bend (flanged) One (1) gate valve 1/4 closed.	One (1) ball valve 1/3 closed.

 

 

Figure Q4: Pipeline System.

 

Q4 CONT…/

/Q4 CONT…

 

1. Calculate the height in both manometers ?_?,?? and ?_?,??.  You are required to show every step of your working and the reasons behind the use of each equation.  For any calculations, if you have used an excel file, please upload your excel file as well.

(20 Marks)

2. As a Process Engineer, you need to give a recommendation to your team about the limit for some design features and operating conditions in the pipeline.  For operational safety, the maximum physical height available for mercury (Hg) to rise in each of the manometers is ?_?,?? = 1 m and ?_?,?? = 3 m so that no Hg can flow into the pipe.
   1. Explain the effect of changing the mass flow rate in the Inlet A at Section 1.
   2. Explain the effect of changing the fluid viscosity in the Inlet A at Section 1.
   3. Explain the effect of closing the gate valve at Section 2.
   4. Explain the effect of changing the material of the pipeline at Section 2.

 

In your explanation, discuss how each of the criteria above will affect the level of the mercury, and whether they could make a manometer overflow.  You need to identify the manometer that will overflow first by calculating the maximum or minimum value of the parameter altered if all other conditions remain constant as described in Q4(a).  For the calculations, you are advised to create an Excel file to investigate how a change of each parameter affects the manometer height.  This is used to support your reasoning, your workings and your recommendation.  If you have used an Excel file, please upload the Excel file as well in your solution.

(10 Marks)

         

5. A farm makes use of the rainwater by collecting it in a reservoir and distributing it through a network of pipes up a hill.  It uses two centrifugal pumps to bring water from the reservoir into two rectangular channels that run completely full of water through the farm until discharging at atmospheric pressure in a pool (see Figure Q5 on Page 9 of this examination paper).  The difference between the level of the pool and the reservoir is 10 m.  Both channels are made of cement (e/D = 0.03), with a square cross-section with a side 0.2 m long.  You are asked to buy two pumps to be installed by the side of the reservoir to pump a flow between 60 to 90 m³/s in each of the channels.  The performance curves of the available pumps are given in pages 10 to 13 of this examination paper.

 

1. Obtain and plot the system curves for Channels A and B.
2. Which of the available pumps must be installed in each channel?  Specify the impeller diameter.  What will be the flow through the system?
3. Calculate the hydraulic power, the power consumed and the efficiency of each pump.
4. If you could adjust the revolutions, which would be the required rpm to obtain 85 m³/s of flow through each channel?

(25 Marks)

 

 

 

 

 

 

 

 

 

 

 

 

Q5 CONT…/

/Q5 CONT…

 

Table Q5: Channel elements: valves, bends, and fittings.

Channel A	Channel B
1 x 120 deg bend cement,    Le/D = 20  1 butterfly gate (100% open)	1 x 120 deg bend cement, Le/D = 20  1 x 90 deg bend cement,   Le/D = 50  1 butterfly gate. It is broken and fix at 75% closed.

 

Butterfly gate:

100 % open  Le/D      =    30

75 % open    Le/D      =    80

50 % open    Le/D      =  200

25 % open    Le/D      =  500

 

 

 

Figure Q5: Square irrigation channels.

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