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THE UNIVERSITY OF TRINIDAD & TOBAGO FINAL ASSESSMENT/EXAMINATIONS DECEMBER 2012 ALTERNATE EXAMINATION Course Code and Title:

HYDR211D Fluids and Hydraulics

Programme:

NETD in Civil Engineering

Date and Time: Duration:

PLEASE READ ALL EXAMINATION

3 hours

INSTRUCTIONS CAREFULLY BEFORE YOU BEGIN THIS

Instructions to Candidates 1. This paper has 10 pages (inclusive of this one) and 7 questions. 2. You are required to answer question 1 in Section A, and any 2 questions in Section B and any 2 questions in Section C. 3. You must return this examination paper together with your answer booklet. Key Examination Protocol 1. Students please note that academic dishonesty (or cheating) includes but is not limited to plagiarism, collusion, falsification, replication, taking unauthorised notes or devices into an examination, obtaining an unauthorised copy of the examination paper, communicating or trying to communicate with another candidate during the examination, and being a party to impersonation in relation to an examination. 2. The above mentioned and any other actions which compromise the integrity of the academic evaluation process will be fully investigated and addressed in accordance with UTT’s academic regulations. 3. Please be reminded that speaking without the Invigilator’s permission is NOT allowed.

The University of Trinidad and Tobago December 2012 Final Examinations - Alternate HYDR 211D Fluids and Hydraulics

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SECTION A – This question is compulsory

1) a) Explain using equations, the “principle of continuity” equation. (2 marks) b) Explain how the principle of continuity equation applies to flow into a branched section. (1 marks) c) Water flows through a pipe AB (see Figure 1), of diameter d1 = 50 mm which is in series with a pipe BC of diameter d2 = 75 mm in which the mean velocity v2 = 2 m/s . At C the pipe forks and one branch CD is of diameter d3 such that the mean velocity v3 = 1.5 m/s. The other branch CE is of diameter d4 = 30 mm and conditions are such that the discharges Q2 from BC divides so that Q4 = ½ Q3. Calculate the values of Q1 , V1, Q2 , Q3, d3, Q4 and v4 . (7 marks)

Figure 1 – Branch Pipe Network – for question 1

The University of Trinidad and Tobago December 2012 Final Examinations - Alternate HYDR 211D Fluids and Hydraulics

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SECTION B – Answer any two (2) questions 2) a) What is vapour pressure? (1 mark) b) Define NPSH. (1 mark) c) Why do pump manufacturers specify NPSH? (1 mark) d) Define cavitation. (1 mark) e) Determine the available NPSH for the system shown in Figure 2. The reservoir is a closed tank with a pressure of -25kPa above water at 70 deg C. The atmospheric pressure is 100.5kPa. The water level in the tank is 3.0 m above the pump inlet. The pipe is a 1½ inch Schedule 40 steel pipe with a total length of 14.0 m. The elbow is standard and the valve is a fully open globe valve. The flow rate is 0.01 m3/min. Given that hvp = 3.25 m at 700 C. Use attached Table 1a and Table 1b to get equivalent lengths (L/D) and fT values. Hint: Also given D/ έ = 889 and kinematic viscosity V = 4.6 x 10 -5 m2/s use moody diagram to get friction factor f, for the Schedule 40 pipe. And for 1½ inch Schedule 40 steel pipe , the inside diameter is 40.9 mm and flow area is 1.314 x 10-2 m2 . (6 marks)

Figure 2 – Pump suction line details - for question 2 The University of Trinidad and Tobago December 2012 Final Examinations - Alternate HYDR 211D Fluids and Hydraulics

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3) a) What are factors to be considered when selecting a pump? (3 marks) b) What is the use of the specific speed of pumps? (1 mark) c) Calculate the specific speed of this pump. (2 marks) d) Assume that a pump is operating with the following performance data at 1200 rpm?

Q 1 – Capacity

Power required P1

Total head h1

1500 gal /min

55 hp

145 ft

When the speed is changed to 1700 rpm, calculate the new performance data of capacity Q2, power P2, and total head delivered h2. (4 marks)

4) a) State the general energy equation. (1 mark) b) State some restrictions in the use of the general energy equation. (2 marks) c) In the system below (see Figure 3), water flows from a large tank at a rate of 1.20 ft3/s. Calculate the total amount of energy lost from the system because of the valve, elbows, the pipe entrance and fluid friction (conversion 1.20 ft3/s = 0.0339 m3/s). (7 marks)

The University of Trinidad and Tobago December 2012 Final Examinations - Alternate HYDR 211D Fluids and Hydraulics

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3.6 3.6mm

3.9 m 3.9 m

0.075 m m 0.075

Figure 3 – for question 4

The University of Trinidad and Tobago December 2012 Final Examinations - Alternate HYDR 211D Fluids and Hydraulics

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SECTION C – Answer any two (2) questions 5) a) State the formula for wetted perimeter and Froude’s number. (2 marks) b) As shown in Figure 4 below, water is being discharged from a reservoir under a sluice gate at the rate of 25 m3/s into a horizontal rectangular channel, 3 m wide, made of unfinished formed concrete. At a point where the depth is 1 m, a hydraulic jump is observed to occur. Determine the following: i. The velocity before the jump. ii. The depth after the jump. iii. The velocity after the jump. iv. The energy dissipated in the jump. (8 marks)

Figure 4 – for question 5

6) a) Determine whether the flow is laminar or turbulent if water at 70 °C in a copper tube of dimensions D = 0.02527 m and kinematic viscosity, V = 4.11 x 10-7 m2/s with a flow rate of 0.27 m3/min. (3 marks) b) State two (2) reasons for creating turbulent flow. (2 marks)

The University of Trinidad and Tobago December 2012 Final Examinations - Alternate HYDR 211D Fluids and Hydraulics

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c) Determine the energy loss using Darcy’s equation, if glycerine at 25 °C flows 40 m through a 200 mm diameter pipe with an average velocity of 5.0 m/s. Given for glycerine at 25 °C, ρ = 1258 kg/m3 and dynamic viscosity ŋ = 9.60 x10-1 Pa.s. (5 marks) 7) a) Determine the minimum slope on which the channel shown in Figure 5 below must be laid, if it is to carry 1.4 m3 of water with a depth of 0.66 m. The sides and bottom of the channel are made of unfinished concrete. Given the equation Q = (1.00 / n ) AR 2/3 S ½ . Manning’s n for concrete n = 0.017. (3 marks)

2.4 m

1.2 m

0.66 m

Figure 5 – for question 7

b) Design a rectangular channel to be made of smooth earth to carry 8.5 m3/s of water when laid on a 1.5 percent slope. The normal depth should be one half the width of the channel bottom. Given the equation AR 2/3 = n Q S ½ , and the value for Manning’s n for smooth earth, n = 0.018 (7 marks)

The University of Trinidad and Tobago December 2012 Final Examinations - Alternate HYDR 211D Fluids and Hydraulics

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Table 1a – Resistance in Valve and Fittings expressed in Equivalent Length in Pipe Diameters, LE/D

Table 1b- Friction Factor in zone of complete turbulence for New Clean Commercial Steel Pipe

The University of Trinidad and Tobago December 2012 Final Examinations - Alternate HYDR 211D Fluids and Hydraulics

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Figure 6 – Moody’s Diagram The University of Trinidad and Tobago December 2012 Final Examinations - Alternate HYDR 211D Fluids and Hydraulics

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RELATION BETWEEN PRESSURE HEAD, ELEVATION HEAD, VELOCITY HEAD AND TOTAL HEAD.

The University of Trinidad and Tobago December 2012 Final Examinations - Alternate HYDR 211D Fluids and Hydraulics

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