Questions and Answers of Fundamentals Thermal Fluid

A paratrooper and his 8-m-diameter parachute weigh 950 N. Taking the average air density to be 1.2 kg/m3, determine the terminal velocity of the paratrooper. 950 N
A commercial airplane has a total mass of 150,000 lbm and a wing planform area of 1800 ft2. The plane has a cruising speed of 550 mi/h and a cruising altitude of 38,000 ft where the air density is
The passenger compartment of a minivan traveling at 50 mi/h in ambient air at 1 atm and 80°F is modeled as a 4.5-ft-high, 6-ft-wide, and 11-ft-long rectangular box. The airflow over the exterior
The cylindrical chimney of a factory has an external diameter of 1.1 m and is 20 m high. Determine the bending moment at the base of the chimney when winds at 110 km/h are blowing across it. Take the
Reconsider Prob. 15€“89. Using an appropriate software, investigate the effect of boat speed on the drag force acting on the bottom surface of the boat, and the power needed to overcome it.
A plastic boat whose bottom surface can be approximated as a 1.5-m-wide, 2-m-long flat surface is to move through water at 15°C at speeds up to 45 km/h. Determine the friction drag exerted on the
A 2-m-high, 4-m-wide rectangular advertisement panel is attached to a 4-m-wide, 0.15-m-high rectangular concrete block (density 5 2300 kg/m3) by two 5-cm-diameter, 4-m-high (exposed part) poles, as
A 1.2-m-external-diameter spherical tank is located outdoors at 1 atm and 25°C and is subjected to winds at 48 km/h. Determine the drag force exerted on it by the wind.
Consider a blimp that can be approximated as a 3-m diameter, 8-m long ellipsoid and is connected to the ground. On a windless day, the rope tension due to the net buoyancy effect is measured to be
An airplane has a mass of 50,000 kg, a wing area of 300 m2, a maximum lift coefficient of 3.2, and a cruising drag coefficient of 0.03 at an altitude of 12,000 m. Determine(a) The takeoff speed at
A small airplane has a total mass of 1800 kg and a wing area of 42 m2. Determine the lift and drag coefficients of this airplane while cruising at an altitude of 4000 m at a constant speed of 280
Consider a light plane that has a total weight of 11,000 N and a wing area of 39 m2and whose wings resemble the NACA 23012 airfoil with no flaps. Using data from Fig. 11€“45, determine the
The NACA 64(l)–412 airfoil has a lift-to-drag ratio of 50 at 0° angle of attack, as shown in Fig. 15–43. At what angle of attack does this ratio increase to 80?
Reconsider Prob. 15–80. Using an appropriate software, investigate the effect of passenger count on the takeoff speed of the aircraft. Let the number of passengers vary from 0 to 500 in increments
A jumbo jet airplane has a mass of about 400,000 kg when fully loaded with over 400 passengers and takes off at a speed of 250 km/h. Determine the takeoff speed when the airplane has 100 empty seats.
An airplane is consuming fuel at a rate of 7 gal/min when cruising at a constant altitude of 10,000 ft at constant speed. Assuming the drag coefficient and the engine efficiency to remain the same,
Consider an airplane whose takeoff speed is 220 km/h and that takes 15 s to take off at sea level. For an airport at an elevation of 1600 m (such as Denver), determine(a) The takeoff speed,(b) The
Consider an aircraft that takes off at 260 km/h when it is fully loaded. If the weight of the aircraft is increased by 10 percent as a result of overloading, determine the speed at which the
A small aircraft has a wing area of 35 m2, a lift coefficient of 0.45 at takeoff settings, and a total mass of 4000 kg. Determine(a) The takeoff speed of this aircraft at sea level at standard
How do flaps affect the lift and the drag of wings?
Explain why endplates or winglets are added to some airplane wings.
What is induced drag on wings? Can induced drag be minimized by using long and narrow wings or short and wide wings?
What is the effect of wing tip vortices (the air circulation from the lower part of the wings to the upper part) on the drag and the lift?
Why are flaps used at the leading and trailing edges of the wings of large aircraft during takeoff and landing? Can an aircraft take off or land without them?
Both the lift and the drag of an airfoil increase with an increase in the angle of attack. In general, which increases at a higher rate, the lift or the drag?
Air is flowing past a symmetrical airfoil at zero angle of attack. Is the(a) Lift(b) Drag acting on the airfoil zero or nonzero?
Air is flowing past a nonsymmetrical airfoil at zero angle of attack. Is the(a) Lift(b) Drag acting on the airfoil zero or nonzero?
What is stall? What causes an airfoil to stall? Why are commercial aircraft not allowed to fly at conditions near stall?
Why is the contribution of viscous effects to lift usually negligible for airfoils?
A person extends his uncovered arms into the windy air outside at 1 atm and 60°F and 25 mi/h in order to feel nature closely. Treating the arm as a 2-ft-long and 4-indiameter cylinder, determine
A 6-mm-diameter electrical transmission line is exposed to windy air. Determine the drag force exerted on a 160-m-long section of the wire during a windy day when the air is at 1 atm and 15°C and
A 2-m-long, 0.2-m-diameter cylindrical pine log (density = 513 kg/m3) is suspended by a crane in the horizontal position. The log is subjected to normal winds of 40 km/h at 5°C and 88 kPa.
Dust particles of diameter 0.06 mm and density 1.6 g/cm3 are unsettled during high winds and rise to a height of 200 m by the time things calm down. Estimate how long it takes for the dust particles
A 1.2-in-outer-diameter pipe is to span across a river at a 140-ft-wide section while being completely immersed in water. The average flow velocity of the water is 10 ft/s, and its temperature is
Consider 0.8-cm-diameter hail that is falling freely in atmospheric air at 1 atm and 5°C. Determine the terminal velocity of the hail. Take the density of hail to be 910 kg/m3.
A long 5-cm-diameter steam pipe passes through some area open to the wind. Determine the drag force acting on the pipe per unit of its length when the air is at 1 atm and 10°C and the wind is
A 0.1-mm-diameter dust particle whose density is 2.1 g/cm3 is observed to be suspended in the air at 1 atm and 25°C at a fixed point. Estimate the updraft velocity of air motion at that location.
In flow over cylinders, why does the drag coefficient suddenly drop when the boundary layer becomes turbulent? Isn’t turbulence supposed to increase the drag coefficient instead of decreasing it?
In flow over bluff bodies such as a cylinder, how does the pressure drag differ from the friction drag?
Why is flow separation in flow over cylinders delayed when the boundary layer is turbulent?
The weight of a thin flat plate 50 cm Ã— 50 cm in size is balanced by a counterweight that has a mass of 2 kg, as shown in Fig. P15€“54. Now a fan is turned on, and air at 1 atm
During a winter day, wind at 55 km/h, 5°C, and 1 atm is blowing parallel to a 4-m-high and 10-m-long wall of a house. Approximating the wall surfaces as smooth, determine the friction drag acting
Repeat Prob. 15–51 for water.Repeat Prob.Air at 25°C and 1 atm is flowing over a long flat plate with a velocity of 8 m/s. Determine the distance from the leading edge of the plate where the flow
Air at 25°C and 1 atm is flowing over a long flat plate with a velocity of 8 m/s. Determine the distance from the leading edge of the plate where the flow becomes turbulent, and the thickness of the
Reconsider Prob. 15€“49E. Using an appropriate software, investigate the effect of truck speed on the total drag force acting on the top and side surfaces, and the power required to
Consider a refrigeration truck traveling at 70 mi/h at a location where the air is at 1 atm and 80°F. The refrigerated compartment of the truck can be considered to be a 9-ft-wide, 8-ft-high, and
Light oil at 75°F flows over a 22-ft-long flat plate with a free-stream velocity of 6 ft/s. Determine the total drag force per unit width of the plate.
Water at 43.3°C flows over a large plate at a velocity of 30.0 cm/s. The plate is 1.0 m long (in the flow direction), and its surface is maintained at a uniform temperature of 10.0°C. Calculate the
Hot carbon dioxide exhaust gas at 1 atm is being cooled by flat plates. The gas at 220°C flows in parallel over the upper and lower surfaces of a 1.5-m-long flat plate at a velocity of 3 m/s. If the
Hot engine oil at 150°C is flowing in parallel over a flat plate at a velocity of 2 m/s. Surface temperature of the 0.5-mlong flat plate is constant at 50°C. Determine(a) The local convection heat
Parallel plates form a solar collector that covers a roof, as shown in the figure. The plates are maintained at 15°C, while ambient air at 10°C flows over the roof with V = 2 m/s. Determine
Hydrogen gas at 1 atm is flowing in parallel over the upper and lower surfaces of a 3-m-long flat plate at a velocity of 2.5 m/s. The gas temperature is 120°C and the surface temperature of the
Carbon dioxide and hydrogen as ideal gases at 1 atm and −20°C flow in parallel over a flat plate. The flow velocity of each gas is 1 m/s and the surface temperature of the 3-m-long plate is
An array of power transistors, dissipating 6 W of power each, are to be cooled by mounting them on a 25-cm Ã— 25-cm-square aluminum plate and blowing air at 35°C over the plate with a
Repeat Prob. 19€“22 for a location at an elevation of 1610 m where the atmospheric pressure is 83.4 kPa.Repeat Prob.An array of power transistors, dissipating 6 W of power each, are to be
Consider a refrigeration truck traveling at 55 mph at a location where the air temperature is 80°F. The refrigerated compartment of the truck can be considered to be a 9-ft-wide, 8-ft-high, and
Consider a hot automotive engine, which can be approximated as a 0.5-m-high, 0.40-m-wide, and 0.8-m-long rectangular block. The bottom surface of the block is at a temperature of 100°C and has an
Air at 1 atm is flowing in parallel over a 3-mlong flat plate with a velocity of 7 m/s. The air has a free stream temperature of 120°C and the surface temperature of the plate is maintained at
The local atmospheric pressure in Denver, Colorado (elevation 1610 m), is 83.4 kPa. Air at this pressure and at 30°C flows with a velocity of 6 m/s over a 2.5-m × 8-m flat plate whose temperature
Warm air is blown over the inner surface of an automobile windshield to defrost ice accumulated on the outer surface of the windshield. Consider an automobile windshield (kw = 0.8 Btu/h·ft·R) with
The top surface of the passenger car of a train moving at a velocity of 70 km/h is 2.8 m wide and 8 m long. The top surface is absorbing solar radiation at a rate of 200 W/m2, and the temperature of
Solar radiation is incident on the glass cover of a solar collector at a rate of 700 W/m2. The glass transmits 88 percent of the incident radiation and has an emissivity of 0.90. The entire hot water
Liquid mercury at 250°C is flowing with a velocity of 0.3 m/s in parallel over a 0.1-m-long flat plate where there is an unheated starting length of 5 cm. The heated section of the flat plate is
A 15 mm × 15 mm silicon chip is mounted such that the edges are flush in a substrate. The chip dissipates 1.4 W of power uniformly, while air at 20°C (1 atm) with a velocity of 25 m/s is used to
The upper surface of a metal plate is being cooled with parallel air flow while its lower surface is subjected to a uniform heat flux of 810 W/m2. The air has a free stream velocity and temperature
Air is flowing in parallel over the upper surface of a flat plate with a length of 4 m. The first half of the plate length, from the leading edge, has a constant surface temperature of 50°C. The
A 15-cm × 15-cm circuit board dissipating 20 W of power uniformly is cooled by air, which approaches the circuit board at 20°C with a velocity of 6 m/s. Disregarding any heat transfer from the back
A long 8-cm-diameter steam pipe whose external surface temperature is 90°C passes through some open area that is not protected against the winds. Determine the rate of heat loss from the pipe per
A heated long cylindrical rod is placed in a cross flow of air at 20°C (1 atm) with velocity of 10 m/s. The rod has a diameter of 5 mm and its surface has an emissivity of 0.95. If the surrounding
A person extends his uncovered arms into the windy air outside at 54°F and 20 mph in order to feel nature closely. Initially, the skin temperature of the arm is 86°F. Treating the arm as a
Reconsider Prob. 19€“44E. Using an appropriate software, investigate the effects of air temperature and wind velocity on the rate of heat loss from the arm. Let the air temperature vary
A 6-mm-diameter electrical transmission line carries an electric current of 50 A and has a resistance of 0.002 ohm/m length. Determine the surface temperature of the wire during a windy day when the
Reconsider Prob. 19€“47. Using an appropriate software, investigate the effect of the wind velocity on the surface temperature of the wire. Let the wind velocity vary from 10 km/h to 80
A long aluminum wire of diameter 3 mm is extruded at a temperature of 280°C. The wire is subjected to cross air flow at 20°C at a velocity of 6 m/s. Determine the rate of heat transfer from
Consider a person who is trying to keep cool on a hot summer day by turning a fan on and exposing his entire body to air flow. The air temperature is 85°F and the fan is blowing air at a velocity
A 0.4-W cylindrical electronic component with diameter 0.3 cm and length 1.8 cm and mounted on a circuit board is cooled by air flowing across it at a velocity of 240 m/min. If the air temperature is
Consider a 50-cm-diameter and 95-cm-long hot water tank. The tank is placed on the roof of a house. The water inside the tank is heated to 80°C by a flat-plate solar collector during the day. The
Reconsider Prob. 19–53. Using an appropriate software, plot the temperature of the tank as a function of the cooling time as the time varies from 30 min to 5 h and discuss the results.Reconsider
During a plant visit, it was noticed that a 12-m-long section of a 10-cm-diameter steam pipe is completely exposed to the ambient air. The temperature measurements indicate that the average
A 10-cm-diameter, 30-cm-high cylindrical bottle contains cold water at 3°C. The bottle is placed in windy air at 27°C. The water temperature is measured to be 11°C after 45 min of cooling.
An average person generates heat at a rate of 84 W while resting. Assuming one-quarter of this heat is lost from the head and disregarding radiation, determine the average surface temperature of the
An incandescent lightbulb is an inexpensive but highly inefficient device that converts electrical energy into light. It converts about 10 percent of the electrical energy it consumes into light
A 1.8-m-diameter spherical tank of negligible thickness contains iced water at 0°C. Air at 25°C flows over the tank with a velocity of 7 m/s. Determine the rate of heat transfer to the tank and the
The components of an electronic system are located in a 1.5-m-long horizontal duct whose cross section is 20 cm Ã— 20 cm. The components in the duct are not allowed to come into direct
Repeat Prob. 19€“61 for a location at 3000-m altitude where the atmospheric pressure is 70.12 kPa.
A coated sheet is being dried with hot air blowing in cross flow on the sheet surface. The surface temperature of the sheet is constant at 90°C, while the air velocity and temperature are 0.3 m/s
Reconsider Prob. 19€“63. Using an appropriate software, evaluate the hot air velocity on the convection heat transfer coefficient. By varying the hot air velocity from 0.15 to 0.35 m/s,
How is the thermal entry length defined for flow in a tube? In what region is the flow in a tube fully developed?
Consider laminar forced convection in a circular tube. Will the heat flux be higher near the inlet of the tube or near the exit? Why?
Consider turbulent forced convection in a circular tube. Will the heat flux be higher near the inlet of the tube or near the exit? Why?
What does the logarithmic mean temperature difference represent for flow in a tube whose surface temperature is constant? Why do we use the logarithmic mean temperature instead of the arithmetic mean
Consider fluid flow in a tube whose surface temperature remains constant. What is the appropriate temperature difference for use in Newton’s law of cooling with an average heat transfer coefficient?
What is the physical significance of the number of transfer units NTU = hAs /mcp? What do small and large NTU values tell about a heat transfer system?
Air enters a 25-cm-diameter 12-m-long underwater duct at 50°C and 1 atm at a mean velocity of 7 m/s, and is cooled by the water outside. If the average heat transfer coefficient is 85 W/m2∙K and
Combustion gases passing through a 3-cminternal-diameter circular tube are used to vaporize waste water at atmospheric pressure. Hot gases enter the tube at 115 kPa and 250°C at a mean velocity of 5
Repeat Prob. 19–72 for a heat transfer coefficient of 40 W/m2∙K.Combustion gases passing through a 3-cminternal-diameter circular tube are used to vaporize waste water at atmospheric pressure.
Cooling water available at 10°C is used to condense steam at 30°C in the condenser of a power plant at a rate of 0.15 kg/s by circulating the cooling water through a bank of 5-m-long
Repeat Prob. 19–74 for steam condensing at a rate of 0.60 kg/s.Cooling water available at 10°C is used to condense steam at 30°C in the condenser of a power plant at a rate of 0.15 kg/s by
Reconsider Prob. 19–74. Using an appropriate software, investigate the effect of the cooling water average (mean) velocity on the number of tubes needed to achieve the indicated heat transfer rate
Inside a condenser, there is a bank of seven copper tubes with cooling water flowing in them. Steam condenses at a rate of 0.6 kg/s on the outer surfaces of the tubes that are at a constant

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