Fluid Mechanics: Fundamentals and Applications
4th Edition
ISBN: 9781259696534
Author: Yunus A. Cengel Dr., John M. Cimbala
Publisher: McGraw-Hill Education
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Textbook Question
Chapter 11, Problem 25EP
To reduce the drag coefficient and thus to improve the fuel efficiency, the frontal area of a car is to be reduced. Determine the amount of fuel and money saved per year as a result of reducing the frontal area from 20 to 13 ft2. Assume the car is driven 12.000 mi a year at an average speed of 55 mi/h. Take the density and price of gasoline to be 50 Ibm/ft3 and $3.10/gal, respectively; the density of air to be 0.075 Ibm ft3, the heating value of gasoline to be 20.000 Btu/Ibm: and the overall efficiency of the drive train to be 30 percent.
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To reduce the drag coefficient and thus to improve the fuel efficiency, the frontal area of a car is to be reduced. Determine the amount of fuel and money saved per year as a result of reducing the frontal area from 17 to 14 ft2. Assume the car is driven 10,000 mi a year at an average speed of 55 mi/h. Take the density and price of gasoline to be 50 lbm/ft3 and $3.10/gal, respectively; the density of air to be 0.075 lbm/ft3; the heating value of gasoline to be 20,000 Btu/lbm; and the overall efficiency of the engine to be 30%.
To reduce the drag coefficient and thus to improve the fuel efficiency, the frontal area of a car is to be reduced. Determine the amount of fuel and money saved per year as a result of reducing the frontal area from 18 to 15 ft2. Assume the car is driven 12,000 mi a year at an average speed of 55 mi/h. Take the density and price of gasoline to be 50 lbm/ft3 and $3.10/gal, respectively; the density of air to be 0.075 lbm/ft3; the heating value of gasoline to be 20,000 Btu/lbm; and the overall efficiency of the engine to be 30 percent.
3. A truck has a drag coefficient based on frontal area of CD = 0.86. The truck has a mass of 12,750 kg and
a frontal area of 10.5 m2. If the truck is traveling at constant speed on a level road, the forces retarding its
forward progress are the drag and the rolling friction. The force due to rolling friction can be written as
Fit Wfr(1+
V
V₁
where V is the truck speed in m/s, Vo = 30 m/s and fr (the coefficient of rolling resistance) is approximately
0.008 for a truck on concrete or asphalt. Plot the total power the engine must supply as a function of truck
speed, V. Comment on the relative importance of drag and rolling friction in the fuel consumption of the
truck.
Chapter 11 Solutions
Fluid Mechanics: Fundamentals and Applications
Ch. 11 - What is drag? What causes it? Why do we usually...Ch. 11 - Prob. 2CPCh. 11 - Which bicyclist is more likely to go faster: one...Ch. 11 - Prob. 4CPCh. 11 - Define the frontal area of a body subjected to...Ch. 11 - Define the planform area of a body subjected to...Ch. 11 - Prob. 7CPCh. 11 - What is the difference between streamlined and...Ch. 11 - Prob. 9CPCh. 11 - During flow over a given body, the drag force, the...
Ch. 11 - During flow over a given slender body such as a...Ch. 11 - What is terminal velocity? How is it determined?Ch. 11 - What is the difference between skin friction drag...Ch. 11 - What is the effect of surface roughness on the...Ch. 11 - Prob. 15CPCh. 11 - What is flow separation? What causes it? What is...Ch. 11 - Prob. 17CPCh. 11 - Consider laminar flow over a flat plate. How does...Ch. 11 - In general, how does the drag coefficient vary...Ch. 11 - Fairings are attached to the front and back of a...Ch. 11 - Prob. 21PCh. 11 - The resultant of the pressure and wall shear...Ch. 11 - Prob. 23PCh. 11 - Prob. 24PCh. 11 - To reduce the drag coefficient and thus to improve...Ch. 11 - A circular sign has a diameter of 50 cm and is...Ch. 11 - Prob. 28PCh. 11 - Prob. 29PCh. 11 - At highway speeds, about half of the power...Ch. 11 - A submarine can be treated as an ellipsoid with a...Ch. 11 - A 70-kg bicyclist is riding her 1 5-kg bicycle...Ch. 11 - A wind turbine with two or four hollow...Ch. 11 - During steady motion of a vehicle on a level road,...Ch. 11 - Prob. 37EPCh. 11 - A 0.80-m-diameter, 1 .2-rn-high garbage can is...Ch. 11 - An 8-mm-diameter plastic sphere whose density is...Ch. 11 - Prob. 40PCh. 11 - The drag coefficient of a vehicle increases when...Ch. 11 - To reduce the drag coefficient and thus to improve...Ch. 11 - During major windstorms, high vehicles such as RVs...Ch. 11 - What does the friction coefficient represent in...Ch. 11 - What fluid property is responsible for the...Ch. 11 - How is the average friction coefficient determined...Ch. 11 - Prob. 47EPCh. 11 - The local atmospheric pressure in Denver, Colorado...Ch. 11 - Prob. 50PCh. 11 - Prob. 51EPCh. 11 - Air at 25C and 1 atm is flowing over a long flat...Ch. 11 - Prob. 54PCh. 11 - During a winter day, wind at 70 km/h, 5C , and I...Ch. 11 - Prob. 56PCh. 11 - The forming section of a plastics plant puts out a...Ch. 11 - Prob. 58CPCh. 11 - Why is flow separation in flow over cylinders...Ch. 11 - Prob. 60CPCh. 11 - A 5-mm-diameter electrical transmission line is...Ch. 11 - A 1ong 5-cm-diameter steam pipe passes through...Ch. 11 - Consider 0.8-cm-diameter hail that is falling...Ch. 11 - Prob. 64EPCh. 11 - Prob. 65PCh. 11 - Prob. 66PCh. 11 - Prob. 67EPCh. 11 - One of the popular demonstrations in science...Ch. 11 - Prob. 69PCh. 11 - What is stall? What causes an airfoil to stall?...Ch. 11 - Prob. 71CPCh. 11 - Air is flowing past a symmetrical airfoil at zero...Ch. 11 - Both the lift and the drag of an airfoil increase...Ch. 11 - Prob. 74CPCh. 11 - Prob. 75CPCh. 11 - Air is flowing past a symmetrical airfoil at an...Ch. 11 - Prob. 77CPCh. 11 - Prob. 78CPCh. 11 - Prob. 79CPCh. 11 - Prob. 80CPCh. 11 - How do flaps affect the lift and the drag of...Ch. 11 - Prob. 82EPCh. 11 - Consider an aircraft that takes off at 260 km/h...Ch. 11 - Prob. 84PCh. 11 - Prob. 85PCh. 11 - A tennis ball with a mass of 57 and a diameter of...Ch. 11 - A small aircraft has a wing area of 40 m2, a lift...Ch. 11 - Prob. 89PCh. 11 - Consider a light plane that has a total weight of...Ch. 11 - A small airplane has a total mass of 1800 kg and a...Ch. 11 - An airplane has a mass of 48.000 k. a wins area of...Ch. 11 - Prob. 93EPCh. 11 - Prob. 94PCh. 11 - Prob. 95EPCh. 11 - A 2-zn-high, 4-zn-wide rectangular advertisement...Ch. 11 - 11-97 A plastic boat whose bottom surface can be...Ch. 11 - Prob. 99PCh. 11 - Prob. 100EPCh. 11 - A commercial airplane has a total mass of 150.000...Ch. 11 - Prob. 102PCh. 11 - Prob. 103PCh. 11 - Prob. 104PCh. 11 - Prob. 105PCh. 11 - Prob. 107PCh. 11 - Prob. 108PCh. 11 - Prob. 109PCh. 11 - Prob. 110PCh. 11 - Prob. 111PCh. 11 - Prob. 113PCh. 11 - Prob. 115PCh. 11 - Prob. 116PCh. 11 - Prob. 117PCh. 11 - Prob. 118PCh. 11 - Prob. 119PCh. 11 - The region of flow trailing the body where the...Ch. 11 - Prob. 121PCh. 11 - Prob. 122PCh. 11 - Prob. 123PCh. 11 - Prob. 124PCh. 11 - Prob. 125PCh. 11 - Prob. 126PCh. 11 - An airplane has a total mass of 3.000kg and a wing...Ch. 11 - Prob. 128PCh. 11 - Write a report on the history of the reduction of...Ch. 11 - Write a report oil the flips used at the leading...Ch. 11 - Discuss how to calculate drag force a unsteady...Ch. 11 - Large commercial airplanes cruise at high...Ch. 11 - Many drivers turn off their air conditioners and...Ch. 11 - Consider the boundary layer growing on a flat...
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, mechanical-engineering and related others by exploring similar questions and additional content below.Similar questions
- At highway speeds, about half of the power generated by the car’s engine is used to overcome aerodynamic drag, and thus the fuel consumption is nearly proportional to the drag force on a level road. Determine the percentage increase in fuel consumption of a car per unit time when a person who normally drives at 55 mi/h now starts driving at 70 mi/h.arrow_forwardA truck has a drag coefficient based on frontal area of CD = 0:86. The truck has a mass of 12,750 kg and a frontal area of 10.5 m2. If the truck is traveling at constant speed on a level road, the forces retarding its forward progress are the drag and the rolling friction. The force due to rolling friction can be written asFrf = W*fr(1 + V/V0)where V is the truck speed in m/s, V0 = 30 m/s and fr (the coe¢ cient of rolling resistance) is approximately 0.008 for a truck on concrete or asphalt. Plot the total power the engine must supply as a function of truck speed, V . Comment on the relative importance of drag and rolling friction in the fuel consumption of the truck.arrow_forwardThe drag coefficient of a vehicle increases when its windows are rolled down or its sunroof is opened. A sports car has a frontal area of 18 ft2 and a drag coefficient of 0.32 when the windows and sunroof are closed. The drag coefficient increases to 0.41 when the sunroof is open. Take the density of air to be 0.075 lbm/ft3. Determine the additional power consumption of the car when the sunroof is opened at (a) 32 mi/h and (b) 70 mi/h.arrow_forward
- Joe recently opened a restaurant and bought a car that has a clean drag area CDA of 3.25 m² and rolling resistance of 700 N at sea level. If he mounts an advertising board as shown in Figure 1, determine the amount of fuel money required per year without the advertising board and the additional amount if the board is installed. The car is estimated to driven 20 000 km a year at an average speed of 50 km/h. Take the density and price of unleaded 95 petrol to be 0.85 kg/h and R 17.12, respectively. Also, consider the density of air to be 1.23 kg/m³, the heating value of 95 petrol to be 46 000 kJ/kg, and overall efficiency of the car's drive train to be 30%. 1.8 m Eat at Joe's Figure 1 0.8 marrow_forwardThe power delivered to the wheels of a car is used to overcome aerodynamic drag. Compare the amount of annual fuel consumption by the car when driving a distance of 24,000 km/year with velocities of 60, 100 and 140 km/h. The drag coefficient and frontal area of the car body are 0.26 and 1.8 m2 and the engine efficiency is 30%. Take the density of air and gasoline as 1.2 and 750 kg/m3. The heating value of gasoline is also 44,000 kJ/kg.arrow_forwardPlease Aspaarrow_forward
- If a 20 hp fishing boat motor can pull a 1150 kg boat with passengers of total mass 120 kg at a constant velocity of 13 m/s, what is the drag force on the boat by the water?arrow_forwardWhile moving into his new apartment, Miguel decides to tie a rope to one of his moving boxes (m = 62 kg) and drag it across the floor with constant speed instead of carrying it. The rope is parallel to the ground as he pulls, and the coefficient of friction between the box and the floor : 0.40. is με = If he drags the box at a constant speed of 1.5 m/s, then what is his power output? If the floor were frictionless, then what power output would be needed to keep the box moving at 1.5 m/s? Try to answer this one conceptually (no calculations) by making use of Newton's first law. Suppose that Miguel pulls the rope so that it makes a slight angle below the horizontal, with the box still maintaining the same speed of 1.5 m/s as before. Will this require an increase or a decrease in his power output? (Hint: what effect does angling the rope downward have on the friction force the box experiences?)arrow_forwardThe drag coefficient of a car at the design conditions of 1 atm, 70°F, and 60 mi/h is to be determined experimentally in a large wind tunnel in a full-scale test. The frontal area of the car is 22.26 ft2. If the force acting on the car in the flow direction is measured to be 68 lbf, determine the drag coefficient of this car.arrow_forward
- The resultant of the pressure and wall shear forces acting on a body is measured to be 470 N, making 33° with the direction of flow. Determine the drag and the lift forces acting on the body.arrow_forwardA 3000 kg car accelerates from rest. The constant forward tractive force of the car is 1000 N and the car experiences a constant drag force of 250 N. Find the distance the car travels in 10 seconds. 1.3 M O 2.5 m O 12.5 m 25.0 marrow_forwardAn engineer designing a light aircraft is trying to make an estimate of the radius of the propeller needed. The design speed of the aircraft is 69m/s into still air and at this speed experience allows the engineer to assume a propeller efficiency of 0.8. Other analysis shows that a thrust of 9296N must be supplied by the propeller to maintain the design speed. Assuming a constant air density of 1.21 kg/m³, determine the radius of the ideal propeller in m to 2 decimal places. Note: Use the propulsive efficiency equation to find the final downstream speed of the air and check that this makes physical sense before calculating the radius.arrow_forward
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