MEEN345-EXAM1-FALL 2021

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Texas A&M University *

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345

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Mechanical Engineering

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Feb 20, 2024

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MEEN345 FALL 2021 Page 1 of 9 1 MEEN 345 FLUID MECHANICS LABORATORY Test #1 You have 90 minutes (one and half hours) to complete the examination. The problems are a mixture of true/false, multiple choice, short answer and workout problems. The exam is an individual assessment and is closed book. You are allowed a calculator, eraser, pen and pencil. You may start scanning your answer using a cell phone or a tablet as soon as you complete the exam. Submit your scanned document to Canvas. After submitting your answer, check if the uploading is successful. Make sure all pages are uploaded and your answer is legible. Return your exam. Show all your work to receive full credit for each question. Write answers clearly and legibly. “On my honor, as an Aggie, I have neither given nor received unauthorized aid on this academic work” __________________________ ___________________________ ___________________ Student Name Signature Section #
MEEN345 FALL 2021 Page 2 of 9 2 Lab 1 Fluid Viscosity and Viscometers (a) Classify each fluid (A, B, and C in the plot) as Newtonian, shear thickening, and/or shear thinning according to the plot below. [6pts] Fluid A Fluid B Fluid C (b) Which curve best represents the flow behavior of motor oil? [4 pts] (c) You took the following data using a viscometer with an unknown liquid. [6 pts] RPM Temp ( ° C) Viscosity (centipoise) 10 25.1 120 20 25.0 121 50 25.2 119 60 25.1 120 100 25.0 120 Which of the following fluids would best fit the given data? Cornstarch and water Blood Ketchup Motor oil (d) For Newtonian Fluids, the viscosity of the fluids do NOT vary with the temperature. Is the statement true or false? [4 pts] True / False
MEEN345 FALL 2021 Page 3 of 9 3 Lab 2 Flow Visualization (a) Water flows through a rectangular cross-section channel as below. The flow velocity in the narrow section was measured. The displacement and time traveled by the water between A and B were L = 15.00 ± 0.05 cm and t = 3.0 ± 0.4 sec, respectively. Determine the velocity of water in the narrow section and uncertainty of the calculated velocity. [8 pts] (b) Determine the mass flow rate and the velocity of the fluid stream in the wider upstream section. Assume that the depth of the channel (into the paper) is 10 mm and the density of water is approximately 1000 kg/m 3 . [8 pts] (c) In the above problem Lab 2 (b), what assumptions were made to determine the mass flow rate in the channel? Select all that apply. [4 pts] _____ the calculated velocity is the average velocity over the cross section of the channel _____ Incompressible fluid (water) _____ Steady flow through the channel _____ Energy conservation through the channel 10 cm B A 3 cm
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MEEN345 FALL 2021 Page 4 of 9 4 Lab 3 Pressure Gage Calibration (a) The dead weight tester is used to calibrate a pressure gage. What pressure in kPa should the pressure gauge read, assuming no errors? Total mass on the piston (including the platform) 𝑀 = 1000 ? , diameter of the piston 𝐷 = 5 ??, ? = 9.8 ?/? 2 . [10 pts] Diameter of piston: 5 mm
MEEN345 FALL 2021 Page 5 of 9 5 (b) The air pressure in a tank is to be measured using a manometer whose open arm is inclined from the horizontal at 30 °. The density of the liquid in the manometer is 1000 kg/m 3 , and the length of the fluid column, L, in the vertical arm above the fluid level in the inclined arm is 15 cm. Determine the absolute pressure of air in the tank . The atmospheric pressure is 100 kPa. Assume the gravitational acceleration is 9.8 ?/? 2 . [10 pts] Tank 30 º L=15 cm
MEEN345 FALL 2021 Page 6 of 9 6 Lab 4 Bernoulli’s Theory The Bernoulli Apparatus was used to examine the flow of water through a divergent passage of rectangular cross section. You measured differential head across the convergent passage with the piezo tubes. (a) H1 and H2 stay constant (H1 > H2). Water is steadily flowing through the convergent channel. In the following figure, the water level in piezo tube 1 is given. Sketch the distribution of water level at piezo tubes 2 and 3 in the Ideal case ( theoretical results ) with steady and incompressible flow. Clearly indicate the heights relative to piezo tube 1. Explain briefly the reason of the distribution of water level . [5 pts] (b) Explain how the distribution of water level in the actual case (experimental results) would be different from your answer in (a). Why? [5 pts] Constant Head Tank Variable Head Tank H1 Piezo Tubes 1 2 3
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MEEN345 FALL 2021 Page 7 of 9 7 (c) The heads at the inlet tank (H1) and outlet tank (H2) indicate 450 mm and 400 mm, respectively. The water flow rate through the channel is 0.05 kg/s. At the middle of the channel, the piezo tube indicates 0.35 m (actual height from the experiment) where the cross-sectional area of the channel is 40 mm 2 . Determine the head loss in the channel from the inlet tank to the piezo tube at the middle of the channel . Assume the gravitational acceleration is 9.8 ?/? 2 . The density of water is approximately 1000 kg/m 3 . [10 pts] Hint : Bernoulli’s equation 𝑃 1 𝜌𝑔 + 𝑉 1 2 2𝑔 + ? 1 = 𝑃 2 𝜌𝑔 + 𝑉 2 2 2𝑔 + ? 2 Constant Head Tank Variable Head Tank H1 H2 Piezo Tube 35 cm
MEEN345 FALL 2021 Page 8 of 9 8 Lab 5 Impact of Jets The “impact of jets” testing apparatus is used to measure the force produced by the jet impinging on the reaction vane. It consists of a water supply pipe surrounded by a transparent plastic shield fitted with a top assembly and flat plate reaction (turning) vane. In operation, water from the hydraulic bench is fed into the unit and a vertical water jet is produced and deflected by the reaction vane. The vane is supported by a pivoted beam, restrained by a spring. Adjusting the jockey weight sets the beam to a balanced position. The impact force by the jet can be also calculated based on the linear momentum change of the jet : 𝐹 𝐽𝑒𝑡 = ?̇ ? 0 (1 − ???𝛽) (1) where ∶ ?𝑎?? ???? ?𝑎??, ? 0 : ???????? ?ℎ𝑎? ??????? ?ℎ? ?𝑎??, 𝛽: ????????? 𝑎???? ?? ?ℎ? ??? The weight beam was initially at balance with the jockey weight at the zero position. You started the hydraulic bench and increased the mass flow rate to be 0.45 kg/s. You moved the jockey weight until the beam balanced again and the distance y from the zero position was 10 cm. Nozzle Area 0.00005 ? 2 Distance between the nozzle and the impact vane, s 3.5 cm Density of water 1000 ??/? 3 Gravitational acceleration 9.8 ?/? 2 Jockey weight 600 g (a) Calculate the impact force by the jet using Equation (1). Neglect the gravitational force on the jet of water. [5 pts]
MEEN345 FALL 2021 Page 9 of 9 9 (b) Determine the impact force by the jet using the experimental result. [5 pts] (c) If the distance (s) between the turning vane (impact surface) and the nozzle increases significantly, how do you expect the impact force to be influenced by this change? Explain. [5 pts] (d) How does the volumetric flow rate through the nozzle affect impact force? Justify your response using mathematical reasoning. [5 pts]
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