MECHANICS of FLUIDS LABORATORY - Mechanical Engineering

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EXPERIMENT 4 MEASUREMENT OF DIFFERENTIAL PRESSURE Pressure can be measured in several ways. Bourdon tube gages, manometers, and transducers are a few of the devices available. Each of these instruments actually measures a difference in pressure; that is, measures a difference between the desired reading and some reference pressure, usually atmospheric. The measurement of differential pressure with manometers is the subject of this experiment. Manometry A manometer is a device used to measure a pressure difference and display the reading in terms of height of a column of liquid. The height is related to the pressure difference by the hydrostatic equation. Figure 4.1 shows a U-tube manometer connected to two pressure vessels. The manometer reading is ∆h and the manometer fluid has density ρ m . One pressure vessel contains a fluid of density ρ 1 while the other vessel contains a fluid of density ρ 2 . The pressure difference can be found by applying the hydrostatic equation to each limb of the manometer. For the left leg, p 1 p 2 1 p A z 1 FIGURE 4.1. A U-tube manometer connected to two pressure vessels. p 1 + ρ 1 gz 1 = p A z 2 Likewise for the right leg, p 2 + ρ 2 gz 2 + ρ m g∆h = p A Equating these expressions and solving for the pressure difference gives h p A m 2 p 1 - p 2 = ρ 2 gz 2 + ρ 1 gz 1 + ρ m g∆h If the fluids above the manometer liquid are both gases, then ρ 1 and ρ 2 are small compared to ρ µ . The above equation then becomes p 1 - p 2 = ρ m g∆h Figure 4.2 is a schematic of the apparatus used in this experiment. It consists of three U-tube manometers, a well-type manometer, a U- tube/inclined manometer and a differential pressure gage. There are two tanks (actually, two capped pieces of pipe) to which each manometer and the gage are connected. The tanks have bleed valves attached and the tanks are connected with plastic tubing to a squeeze bulb. The bulb lines also contain valves. With both bleed valves closed and with both bulb line valves open, the bulb is squeezed to pump air from the low pressure tank to the high pressure tank. The bulb is squeezed until any of the manometers reaches its maximum reading. Now both valves are closed and the liquid levels are allowed to settle in each manometer. The ∆h readings are all recorded. Next, one or both bleed valves are opened slightly to release some air into or out of a tank. The liquid levels are again allowed to settle and the ∆h readings are recorded. The procedure is to be repeated until 5 different sets of readings are obtained. For each set of readings, convert all readings into psi or Pa units, calculate the average value and the standard deviation. Before beginning, be sure to zero each manometer and the gage. Questions 1. Manometers 1, 2 and 3 are U-tube types and each contains a different liquid. Manometer 4 is a well-type manometer. Is there an advantage to using this one over a U-tube type? 2. Manometer 5 is a combined U/tube/inclined manometer. What is the advantage of this type? 3. Note that some of the manometers use a liquid which has a specific gravity different from 1.00, yet the reading is in inches of water. Explain how this is possible. 4. What advantages or disadvantages does the gage have over the manometers? 12
5. Is a low value of the standard deviation expected? Why? 6. What does a low standard deviation imply? 7. In your opinion, which device gives the most accurate reading. What led you to this conclusion? High pressure tank Low pressure tank Bleed valves Gage U-tube manometers Well-type manometer U-tube/inclined manometer FIGURE 4.2. A schematic of the apparatus used in this experiment. 13
Page 1 and 2: A Manual for the MECHANICS of FLUID
Page 3 and 4: TABLE OF CONTENTS Item Page Report
Page 5 and 6: as its strong points. Suggest exten
Page 7 and 8: EXPERIMENT 1 FLUID PROPERTIES: DENS
Page 9 and 10: EXPERIMENT 2 FLUID PROPERTIES: VISC
Page 11: L level R i y zeroing weight torus
Page 15 and 16: pivot balancing weight lever arm wi
Page 17 and 18: Questions 1. Can a similar procedur
Page 19 and 20: actual flow rate (measured in the l
Page 21 and 22: manometer orifice meter venturi met
Page 23 and 24: otameter tank valve motor static pr
Page 25 and 26: Pressure Measurement Equipment A Wi
Page 27 and 28: EXPERIMENT 10 DRAG FORCE DETERMINAT
Page 29 and 30: Experiment II For a number of wings
Page 31 and 32: axis) versus (Q 2 /b 2 h 0 3 g). De
Page 33 and 34: Therefore, Q = ∫ 0 Integration gi
Page 35 and 36: Develop a hydraulic jump in the cha
Page 37 and 38: At any upstream (of the hump) locat
Page 39 and 40: EXPERIMENT 16 MEASUREMENT OF VELOCI
Page 41 and 42: Incompressible Flow Through a Meter
Page 43 and 44: TABLE 16.1. Summary of equations fo
Page 45 and 46: placed on the torque arm to reposit
Page 47 and 48: ∆H = H 2 - H 1 = p 2 ρg + V 2 2
Page 49 and 50: Specific Speed A dimensionless grou
Page 51 and 52: 1 large orifice volume flow rate in

MECHANICS of FLUIDS LABORATORY - Mechanical Engineering

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