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mechanical engineering

Questions and Answers of Mechanical Engineering

In a test of the pump in the figure, the data are: p1 = 100 mmHg (vacuum), p2 = 500 mmHg (gage), D1 = 12 cm, and D2 = 5 cm. The flow rate is 180 gal/min of light oil (SG = 0.91). Estimate(a) The head
A 20-hp pump delivers 400 gal/min of gasoline at 20°C with 80% efficiency. What head and pressure rise result across the pump?
A pump delivers gasoline at 20°C and 12 m3/h. At the inlet, p1 = 100 kPa, z1 = 1 m, and V1 = 2 m/s. At the exit p2 = 500 kPa, z2 = 4 m, and V2 = 3 m/s. How much power is required if the motor
A lawn sprinkler can be used as a simple turbine. As shown in Fig. P11.15, flow enters normal to the paper in the center and splits evenly into Q/2 and Vrel leaving each nozzle. The arms rotate at
For the “sprinkler turbine’’ of Fig P11.15, let R = 18 cm, with total flow rate of 14 m3/h of water at 20°C. If the nozzle exit diameter is 8 mm, estimate (a) The maximum power delivered in W
A centrifugal pump has d1 = 7 in, d2 = 13 in, b1 = 4 in, b2 = 3 in, β1 = 25°, and β2 = 40° and rotates at 1160 r/min. If the fluid is gasoline at 20°C and the flow enters the
A jet of velocity V strikes a vane which moves to the right at speed Vc, as in Fig. P11.18.The vane has a turning angle θ. Derive an expression for the power delivered to the vane by the jet.
A centrifugal water pump has r2 = 9 in, b2 = 2 in, and β2 = 35° and rotates at 1060 r/min. If it generates a head of 180 ft, determine the theoretical (a) Flow rate in gal/min and (b)
Suppose that Prob. 11.19 is reversed into a statement of the theoretical power P = 153 hp. Can you then compute the theoretical? (a) Flow rate; and (b) Head? Explain and resolve the difficulty
The centrifugal pump of Fig P11.21 develops a flow rate of 4200 gpm with gasoline at 20°C and near-radial absolute inflow. Estimate the theoretical(a) Horsepower;(b) Head rise; and(c) Appropriate
A 37-cm-diameter centrifugal pump, running at 2140 rev/min with water at 20°C produces the following performance data: Q, m3/s: 0.0 0.05 0.10 0.15 0.20 0.25 0.30 H, m: 105 104 102
If the 38-in pump from Fig. 11.7(b) is used to deliver 20°C kerosene, at 850 rpm and 22000 gal/min, what (a) Head; and (b) Brake horsepower will result?
Figure P11.24 shows performance data for the Taco, Inc., model 4013 pump. Compute the ratios of measured shutoff head to the ideal value U2/g for all seven impeller sizes. Determine the average and
At what speed in rpm should the 35-in-diameter pump of Fig. 11.7(b) be run to produce a head of 400 ft at a discharge of 20000 gal/min? What brake horsepower will be required? Hint: Fit H (Q) to a
Determine if the seven Taco, Inc. pumps in Fig. 11.24 on the previous page can be collapsed into a single dimensionless chart of CH, CP, and η versus CQ, as in Fig. 11.8 of the text. Comment on
The 12-in pump of Fig P11.24 is to be scaled up in size to provide a head of 90 ft and a flow rate of 1000 gal/min at BEP. Determine the correct (a) Impeller diameter; (b) Speed in rpm; and (c)
Tests by the Byron Jackson Co. of a 14.62-in centrifugal water pump at 2134 rpm yield the data below. What is the BEP? What is the specific speed? Estimate the max discharge. Q, ft3/s: 0 2 4 6
If the scaling laws are applied to the Byron Jackson pump of Prob. 11.28 for the same impeller diameter, determine (a) The speed for which the shut-off head will be 280 ft; (b) The speed for
A pump from the same family as Prob. 11.28 is built with D = 18 in and a BE power of 250 bhp for gasoline (not water). Using the scaling laws, estimate the resulting (a) Speed in rpm; (b) Flow
A centrifugal pump with backward-curved blades has the following measured performance when tested with water at 20°C: Q, gal/min: 0 400 800 1200 1600 2000 2400 H, ft: 123 115 108 101
The data of Prob. 11.31 correspond to a pump speed of 1200 r/min. (Were you able to solve Prob. 11.31 without this knowledge?) (a) Estimate the diameter of the impeller [HINT: See Prob. 11.24 for a
For the pump family of Probs. 11.31 and 11.32, find the appropriate (a) Diameter and (b) Rotation speed which will deliver, at BEP, 5300 gal/min against a head of 210 ft. (c) What is the brake
Consider a pump geometrically similar to the 9-in-diameter pump of Fig. P11.34 to deliver 1200 gal/min of kerosene at 1500 rpm, determine the appropriate(a) Impeller diameter;(b) BEP horsepower;(c)
An 18-in-diameter centrifugal pump, running at 880 rev/min with water at 20°C, generates the following performance data:
Plot the dimensionless performance curves for the pump of Prob. P11.35 and compare with Fig. 11.8 of the text. Find the appropriate diameter in inches and the speed, in rev/min, for a geometrically
Knowing that the pump of Prob. 11.35 has BEP at Q = 8000 gal/min, use the similarity rules to find the appropriate (a) Impeller diameter, (b) Rotation speed, and (c) Head produced for a pump of
A 6.85-in pump, running at 3500 rpm, has the measured performance at right for water at 20°C. (a) Estimate the horsepower at BEP. If this pump is rescaled in water to provide 20 bhp at 3000 rpm,
The Allis-Chalmers D30LR centrifugal compressor delivers 33,000 ft3/min of SO2 with a pressure change from 14.0 to 18.0 lbf/in2 absolute using an 800-hp motor at 3550 r/min. What is the overall
The specific speed Ns, as defined by Eq. (11.30), does not contain the impeller diameter. How then should we size the pump for a given Ns? Logan [7] suggests a parameter called the specific diameter
It is desired to build a centrifugal pump geometrically similar to Prob. 11.28 (data at right) to deliver 6500 gal/min of gasoline at 1060 rpm. Estimate the resulting(a) Impeller diameter;(b)
An 8-inch model pump delivering water at 180°F at 800 gal/min and 2400 rpm begins to cavitate when the inlet pressure and velocity are 12 psia and 20 ft/s, respectively. Find the required NPSH of a
The 28-in-diameter pump in Fig. 11.7a at 1170 r/min is used to pump water at 20°C through a piping system at 14,000 gal/min.(a) Determine the required brake horsepower. The average friction
The pump of Prob. 11.28 is scaled up to an 18-in-diameter, operating in water at BEP at 1760 rpm. The measured NPSH is 16 ft, and the friction loss between the inlet and the pump is 22 ft. Will it be
Determine the specific speeds of the seven Taco, Inc. pump impellers in Fig. P11.24. Are they appropriate for centrifugal designs? Are they approximately equal within experimental uncertainty? If
The answer to Prob. 11.40 is that the dimensionless €œspecific diameter€ takes the form Ds = D (gH*)1/4/Q*1/2, evaluated at the BEP. Data collected by the writer for 30 different
A typical household basement sump pump provides a discharge of 5 gal/min against a head of 15 ft. Estimate? (a) The maximum efficiency; and (b) The minimum horsepower required to drive such a pump.
When operating at 42 r/s near BEP, a pump delivers 0.06 m3/s against a head of 100 m. (a) What is its specific speed? (b) What kind of pump is this likely to be? (c) Estimate its impeller
Data collected by the writer for flow coefficient at BEP for 30 different pumps are plotted at right in Fig. P11.49. Determine if the values of QC* fit this correlation for the pumps of Problems
Data collected by the writer for power coefficient at BEP for 30 different pumps are plotted at right in Fig. P11.50. Determine if the values of C*Q for the FOUR pumps of Prob. 11.49 above fit this
An axial-flow pump delivers 40 ft3/s of air which enters at 20°C and 1 atm. The flow passage has a 10-in outer radius and an 8-in inner radius. Blade angles are α1 = 60° and β 2 = 70°,
An axial-flow fan operates in sea level air at 1200 r/min and has a blade-tip diameter of 1 m and a root diameter of 80 cm. The inlet angles are α1 = 55° and β1 = 30°, while at the outlet
If the axial-flow pump of is used to deliver 70,000 gal/min of 20°C water at 1170 rpm, estimate (a) The proper impeller diameter; (b) The shut-off head; (c) The shut-off horsepower; and (d)
The Colorado River Aqueduct uses Worthington Corp. pumps which deliver 200 ft3/s of water at 450 rpm against a head of 440 ft. What kind of pumps are these? Estimate the impeller diameter.
We want to pump 70°C water at 20,000 gal/min and 1800 rpm. Estimate the type of pump needed, the horsepower required, and the impeller diameter if the required pressure rise for one stage is (a)
A pump is needed to deliver 40,000 gpm of gasoline at 20°C against a head of 90 ft. Find the impeller size, speed, and brake horsepower needed to use the pump families of (a) Fig. 11.8; and (b)
Performance data for a 21-in-diameter air blower running at 3550 rpm are shown below. What is the specific speed? How does the performance compare with Fig. 11.13? What are Q H P C*, C*, C*?
The Worthington Corp. Model A-12251 water pump, operating at maximum efficiency, produces 53 ft of head at 3500 rpm, 1.1 bhp at 3200 rpm, and 60 gal/min at 2940 rpm what type of pump is this? What is
Suppose it is desired to deliver 700 ft3/min of propane gas (molecular weight = 44.06) at 1 atm and 20°C with a single-stage pressure rise of 8.0 in H2O. Determine the appropriate size and speed for
11.60 A 45-hp pump is desired to generate a head of 200 ft when running at BEP with 20°C gasoline at 1200 rpm. Using the correlations in Figs P11.49 and P11.50, determine the appropriate (a)
A mine ventilation fan delivers 500 m3/s of sea-level air at 295 rpm and Δp = 1100 Pa. Is this fan axial, centrifugal, or mixed? Estimate its diameter in feet. If the flow rate is increased 50%
The actual mine-ventilation fan in Prob. 11.61 had a diameter of 20 ft [Ref. 20, p. 339]. What would be the proper diameter for the pump family of Fig. 11.14 to provide 500 m3/s at 295 rpm and BEP?
The 36.75-in pump in Fig. 11.7a at 1170 r/min is used to pump water at 60°F from a reservoir through 1000 ft of 12-in-ID galvanized-iron pipe to a point 200 ft above the reservoir surface. What flow
A leaf blower is essentially a centrifugal impeller exiting to a tube. Suppose that the tube is smooth PVC pipe, 4 ft long, with a diameter of 2.5 in. The desired exit velocity is 73 mi/h in
The 38-inch pump in Fig. 11.7b is used in series to lift 20°C water 3000 ft through 4000-ft of 18-inch-diameter cast iron pipe. For most efficient operation, how many pumps in series are needed if
It is proposed to run the pump of Prob. 11.35 at 880 rpm to pump water at 20°C through the system of Fig. P11.66. The pipe is 20-cm diameter commercial steel. What flow rate in ft3/min results?
The pump of Prob. 11.35, running at 880 r/min, is to pump water at 20°C through 75 m of horizontal galvanized-iron pipe (ε = 0.15 mm). All other system losses are neglected. Determine the flow
Suppose that we use the axial-flow pump of Fig. 11.13 to drive the leaf blower of Prob. 11.64. What approximate (a) Diameter and (b) Rotation speed are appropriate? (c) Is this a good design?
The pump of Prob. 11.38, running at 3500 rpm, is used to deliver water at 20C through 600 ft of cast-iron pipe to an elevation 100 ft higher. Find (a) The proper pipe diameter for BEP
The pump of Prob. 11.28, operating at 2134 rpm, is used with water at 20°C in the system of Fig. P11.70. The diameter is 8 inches.(a) If it is operating at BEP, what is the proper elevation
The pump of Prob. 11.38, running at 3500 r/min, delivers water at 20°C through 7200 ft of horizontal 5-in-diameter commercial-steel pipe. There are a sharp entrance, sharp exit, four 90°
Performance data for a small commercial pump are shown below. The pump supplies 20°C water to a horizontal 5/8-in-diameter garden hose (ε ≈ 0.01 in) which is 50 ft long. Estimate (a)
The piston pump of Fig P11.9 (at right) is run at 1500 rpm to deliver SAE 10W oil through 100 m of vertical 2-cmdiameter wrought-iron pipe. If other system losses are neglected, estimate(a) The flow
The 32-in-diameter pump in Fig. 11.7a is used at 1170 rpm in a system whose head curve is Hs (ft) ≈ 100 + 1.5Q2; with Q in kgal/min. Find the discharge and brake horsepower required for (a)
Two 35-inch pumps from Fig. 11.7b are installed in parallel for the system of Fig. P11.75. Neglect minor losses. For water at 20°C, estimate the flow rate and power required if (a) Both pumps are
Two 32-inch pumps are combined in parallel to deliver water at 20°C through 1500 ft of horizontal pipe. If f = 0.025, what pipe diameter will ensure a flow rate of 35,000 gal/min at 1170 rpm?
Two pumps of the type tested in Prob. 11.22 are to be used at 2140 r/min to pump water at 20°C vertically upward through 100 m of commercial-steel pipe. Should they be in series or in parallel? What
Suppose that the two pumps in Fig. P11.75 are instead arranged to be in series, again at 710 rpm? What pipe diameter is required for BEP operation?
Two 32-inch pumps from Fig. 11.7a are to be used in series at 1170 rpm to lift water through 500 ft of vertical cast-iron pipe. What should the pipe diameter be for most efficient operation? Neglect
It is proposed to use one 32- and one 28-in pump from Fig. 11.7a in parallel to deliver water at 60°F. The system-head curve is Hs = 50 + 0.3Q2, with Q in thousands of gallons per minute. What will
Reconsider the system of Fig. P6.62. Use the Byron Jackson pump of Prob. 11.28 running at 2134 r/min, no scaling, to drive the flow. Determine the resulting flow rate between the reservoirs. What is
The S-shaped head-versus-flow curve in Fig. P11.82 occurs in some axial-flow pumps. Explain how a fairly flat system-loss curve might cause instabilities in the operation of the pump. How might we
The low-shutoff head-versus-flow curve in Fig. P11.83 occurs in some centrifugal pumps. Explain how a fairly flat system-loss curve might cause instabilities in the operation of the pump. What
Turbines are to be installed where the net head is 400 ft and the flow rate is 250,000 gal/min. Discuss the type, number, and size of turbine which might be selected if the generator selected is (a)
Turbines at the Conowingo plant on the Susquehanna River each develop 54,000 bhp at 82 rpm under a head of 89 ft. What type of turbines are these? Estimate the flow rate and impeller diameter.
The Tupperware hydroelectric plant on the Blackstone River has four 36-inchdiameter turbines, each providing 447 kW at 200 rpm and 205 ft3/s for a head of 30 ft, what type of turbines are these? How
An idealized radial turbine is shown in Fig. P11.87. The absolute flow enters at 30° and leaves radially inward. The flow rate is 3.5 m3/s of water at 20°C. The blade thickness is constant at
Performance data for a very small (D = 8.25 cm) model water turbine, operating with an available head of 49 ft, are as follows:(a) What type of turbine is this likely to be?(b) What is so different
A Pelton wheel of 12-ft pitch diameter operates under a new head of 2000 ft. Estimate the speed, power output, and flow rate for best efficiency if the nozzle exit diameter is 4 inches.
An idealized radial turbine is shown in Fig. P11.90. The absolute flow enters at 25° with the blade angles as shown. The flow rate is 8 m3/s of water at 20°C. The blade thickness is constant
The flow through an axial-flow turbine can be idealized by modifying the stator rotor diagrams of Fig. 11.12 for energy absorption. Sketch a suitable blade and flow arrangement and the associated
A dam on a river is being sited for a hydraulic turbine. The flow rate is 1500 m3/h, the available head is 24 m, and the turbine speed is to be 480 r/min. Discuss the estimated turbine size and
Figure P11.93 shown on the following page, shows a cross flow or €œBanki€ turbine [Ref. 55], which resembles a squirrel cage with slotted curved blades. The flow enters at about
A simple cross flow turbine, Fig P11.93 above, was constructed and tested at the University of Rhode Island. The blades were made of PVC pipe cut lengthwise into three 120-arc pieces. When
One can make a theoretical estimate of the proper diameter for a penstock in an impulse turbine installation, as in Fig. P11.95. Let L and H be known, and let the turbine performance be idealized by
Apply the results of Prob. 11.95 to determining the optimum (a) Penstock diameter, and (b) Nozzle diameter for the data of Prob. 11.92, with a commercial-steel penstock of length 1500 ft. [H =
Consider the following non-optimum version of Prob. 11.95: H = 450 m, L = 5 km, D = 1.2 m, Dj = 20 cm. The penstock is concrete, ε = 1 mm. The impulse wheel diameter is 3.2 m. Estimate (a) The
Francis and Kaplan (enclosed) turbines are often provided with draft tubes, which lead the exit flow into the tail water region, as in Fig. P11.98. Explain at least two advantages to using a draft
Like pumps, turbines can also cavitate when the pressure at point 1 in Fig. P11.98 drops too low. With NPSH defined by Eq. 11.20, the empirical criterion given by Wislicenus [Ref. 4] for cavitation
One of the largest wind generators in operation today is the ERDA/NASA two blade propellers HAWT in Sandusky, Ohio. The blades are 125 ft in diameter and reach maximum power in 19 mi/h winds. For
A Darrieus VAWT in operation in Lumsden, Saskatchewan, that is 32 ft high and 20 ft in diameter sweeps out an area of 432 ft2. Estimate (a) The maximum power and (b) The rotor speed if it is
An American 6-ft diameter multiblade HAWT is used to pump water to a height of 10 ft through 3-in-diameter cast-iron pipe. If the winds are 12 mi/h, estimate the rate of water flow in gal/min.
A very large Darrieus VAWT was constructed by the U.S. Department of Energy near Sandia, New Mexico. It is 60 ft high and 30 ft in diameter, with a swept area of 1200 ft2. If the turbine is
The net head of a little aquarium pump is given by the manufacturer as a function of volume flow rate as listed:Q, m3/s: 0 1E−6 2E−6 3E−6 4E−6 5E−6H, mmH2O: 1.10
Reconsider Prob. 6.62 as an exercise in pump selection. Select an impeller size and rotational speed from the Byron Jackson pump family of Prob. 11.28 which will deliver a flow rate of 3 ft3/s to the
Reconsider Prob. 6.77 as an exercise in turbine selection. Select an impeller size and rotational speed from the Francis turbine family of Fig. 11.21d which will deliver maximum power generated by
The system of Fig C11.4 is designed to deliver water at 20C from a sea-level reservoir to another through new cast iron pipe of diameter 38 cm. Minor losses are _K1 0.5 before
In Prob. 11.23, estimate the efficiency of the pump in two ways: (a) Read it directly from Fig. 11.7b (for the dynamically similar pump); (b) Calculate it from Eq. (11.5) for the actual kerosene
An interesting turbo machine [58] is the fluid coupling of Fig. C11.6, which delivers fluid from a primary pump rotor into a secondary turbine on a separate shaft Both rotors have radial blades.
What is the difference between the classical and the statistical approaches to thermodynamics?
Why does a bicyclist pick up speed on a downhill road even when he is not pedaling? Does this violate the conservation of energy principle?

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