Questions and Answers of Fundamentals Of Thermal-Fluid Sciences

A geothermal district heating system involves the transport of geothermal water at 110°C from a geothermal well to a city at about the same elevation for a distance of 12 km at a rate of 1.5 m3/s in
A 4-m-high and 6-m-long wall is constructed of two large 0.8-cm-thick steel plates (k = 15 W/m⋅K) separated by 1-cmthick and 22-cm-wide steel bars placed 99 cm apart. The remaining space
What is lumped system analysis? When is it applicable?
Plasma spraying is a process used for coating a material surface with a protective layer to prevent the material from degradation. In a plasma spraying process, the protective layer in powder form is
Consider a spherical shell satellite with outer diameter of 4 m and shell thickness of 10 mm that is reentering the atmosphere. The shell satellite is made of stainless steel with properties of
A large cast iron container (k = 52 W/m⋅K and α = 1.70 ×  10−5 m2/s) with 4-cm-thick walls is initially at a uniform temperature of 0°C and is filled with ice at 0°C. Now the
Why do skiers get sunburned so easily?
Electricity is generated and transmitted in power lines at a frequency of 50 Hz (1 Hz = 1 cycle per second). Determine the wavelength of the electromagnetic waves generated by the
What is the crossed-strings method? For what kinds of geometries is the crossed-strings method applicable?
A furnace is shaped like a long semi cylindrical duct of diameter D = 15 ft. The base and the dome of the furnace have emissivities of 0.5 and 0.9 and are maintained at uniform temperatures of
A shell-and-tube heat exchanger is used for heating 14 kg/s of oil (cp = 2.0 kJ/kg⋅K) from 20°C to 46°C. The heat exchanger has one shell pass and six tube passes. Water enters the shell side
The boiling temperature of nitrogen at atmospheric pressure at sea level (1 atm pressure) is − 196° C. Therefore, nitrogen is commonly used in low-temperature scientific studies since the
A 4-mm-diameter spherical ball at 50°C is covered by 1-mm-thick plastic insulation (k = 0.13 W/m⋅K). The ball is exposed to a medium at 15°C, with a combined convection and radiation heat
Obtain a relation for the fin efficiency for a fin of constant cross-sectional area Ac, perimeter p, length L, and thermal conductivity k exposed to convection to a medium at T∞ with a heat
Two very long, slender rods of the same diameter and length are given. One rod (Rod 1) is made of aluminum and has a thermal conductivity k1  = 200 W/m ⋅ K, but the thermal conductivity of Rod
A turbine blade made of a metal alloy (k = 17 W/m⋅K) has a length of 5.3 cm, a perimeter of 11 cm, and a cross-sectional area of 5.13 cm2 . The turbine blade is exposed to hot gas from the
Pipes with inner and outer diameters of 50 mm and 60 mm, respectively, are used for transporting superheated vapor in a manufacturing plant. The pipes with thermal conductivity of 16 W/m⋅K are
The plumbing system of a house involves a 0.5-m section of a plastic pipe (k = 0.16 W/m⋅K) of inner diameter 2 cm and outer diameter 2.4 cm exposed to the ambient air. During a cold and windy
A 12-cm-long bar with a square cross section, as shown in Fig. P17–133, consists of a 1-cm-thick copper layer (k = 380 W/m⋅K) and a 1-cm-thick epoxy composite layer (k = 0.4 W/m⋅K).
A transparent film is to be bonded onto the top surface of a solid plate inside a heated chamber. For the bond to cure properly, a temperature of 70°C is to be maintained at the bond, between the
To defrost ice accumulated on the outer surface of an automobile windshield, warm air is blown over the inner surface of the windshield. Consider an automobile windshield with thickness of 5 mm and
The wall of a refrigerator is constructed of fiberglass insulation (k = 0.035 W/m⋅K) sandwiched between two layers of 1-mm-thick sheet metal (k = 15.1 W/m⋅K). The refrigerated space is
Consider a house that has a 10-m × 20-m base and a 4-m-high wall. All four walls of the house have an R-value of 2.31m2⋅°C/ W . The two 10-m × 4-m walls have no windows. The third wall
The thermal contact conductance at the interface of two 1-cm-thick aluminum plates is measured to be 11,000 W/m2 ⋅K. Determine the thickness of the aluminum plate whose thermal resistance is equal
A 1-mm-thick copper plate (k = 401 W/m⋅K) is sandwiched between two 7-mm-thick epoxy boards (k = 0.26 W/m⋅K) that are 15 cm × 20 cm in size. If the thermal contact conductance on
A 4-m-high and 6-m-wide wall consists of a long 15-cm × 25-cm cross section of horizontal bricks (k = 0.72 W/m⋅K) separated by 3-cm-thick plaster layers (k = 0.22 W/m⋅K). There are also
Consider a 1.5-m-high electric hot-water heater that has a diameter of 40 cm and maintains the hot water at 60°C. The tank is located in a small room whose average temperature is 27°C, and the heat
The heat generated in the circuitry on the surface of a silicon chip (k = 130 W/m⋅K) is conducted to the ceramic substrate to which it is attached. The chip is 6 mm × 6 mm in size
In the metal processing industry, heat treatment of metals is commonly done using electrically heated draw batch furnaces. Consider a furnace that is situated in a room with surrounding air
Consider a sealed 20-cm-high electronic box whose base dimensions are 40 cm × 40 cm placed in a vacuum chamber The emissivity of the outer surface of the box is 0.95. If the electronic
A 1.4-m-long, 0.2-cm-diameter electrical wire extends across a room that is maintained at 20° C. Heat is generated in the wire as a result of resistance heating, and the surface temperature of the
An aluminum pan whose thermal conductivity is 237 W/m⋅K has a flat bottom with diameter 15 cm and thickness 0.4 cm. Heat is transferred steadily to boiling water in the pan through its bottom at a
A paratrooper and his 7-m-diameter parachute weigh 1200 N. Taking the average air density to be 1.2 kg/m3, determine the terminal velocity of the paratrooper. -7 m 1200 N FIGURE P15-93
An automotive engine can be approximated as a 0.4-m-high, 0.60-m-wide, and 0.7-m-long rectangular block. The ambient air is at 1 atm and 15°C. Determine the drag force acting on the bottom surface
Stokes’ law can be used to determine the viscosity of a fluid by dropping a spherical object in it and measuring the terminal velocity of the object in that fluid. This can be done by plotting the
A 7-ft-diameter spherical tank completely submerged in fresh water is being towed by a ship at 8 ft/s. Assuming turbulent flow, determine the required towing power.
An airplane has a mass of 48,000 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 2.4-in-diameter smooth ball rotating at 500 rpm is dropped in a water stream at 60°F flowing at 4 ft/s. Determine the lift and the drag force acting on the ball when it is first dropped in the
Air is flowing past a spherical ball. Is the lift exerted on the ball zero or nonzero? Answer the same question if the ball is spinning.
The forming section of a plastics plant puts out a continuous sheet of plastic that is 1.2 m wide and 2 mm thick at a rate of 18 m/min. The sheet is subjected to airflow at a velocity of 4 m/s on
During major windstorms, high vehicles such as RVs and semis may be thrown off the road and boxcars off their tracks, especially when they are empty and in open areas. Consider a 6000-kg semi that is
Suzy likes to drive with a silly sun ball on her car antenna. The frontal area of the ball is A = 2.08 × 10−3 m2. As gas prices rise, her husband is concerned that she is wasting fuel because of
The resultant of the pressure and wall shear forces acting on a body is measured to be 430 N, making 30° with the direction of flow. Determine the drag and the lift forces acting on the body. FIGURE
What is terminal velocity? How is it determined?
Which bicyclist is more likely to go faster: one who keeps his head and his body in the most upright position or one who leans down and brings his body closer to his knees? Why?
Water is transported by gravity through a 10-cm-diameter 550-m-long plastic pipe with an elevation gradient of 0.01 (i.e., an elevation drop of 1 m per 100 m of pipe length). Taking ρ = 1000 kg/m3
Water at 15°C is drained from a large reservoir using two horizontal plastic pipes connected in series. The first pipe is 13 m long and has a 10-cm diameter, while the second pipe is 35 m long and
A horizontal pipe has an abrupt expansion from D1 = 5 cm to D2 = 10 cm. The water velocity in the smaller section is 8 m/s and the flow is turbulent. The pressure in the smaller section is P1 = 410
Consider the fully developed flow of glycerin at 40°C through a 70-m-long, 4-cm-diameter, horizontal, circular pipe. If the flow velocity at the centerline is measured to be 6 m/s, determine the
Water shoots out of a large tank sitting on a cart with frictionless wheels. The water jet velocity is Vj = 7.00 m/s, its cross-sectional area is Aj = 20.0 mm2, and the momentum-flux correction
Consider an airplane with a jet engine attached to the tail section that expels combustion gases at a rate of 18 kg/s with a velocity of V = 300 m/s relative to the plane. During landing, a thrust
A 5-cm-diameter horizontal jet of water with a velocity of 30 m/s relative to the ground strikes a flat plate that is moving in the same direction as the jet at a velocity of 20 m/s. The water
Water enters a 7-cm-diameter pipe steadily with a uniform velocity of 2 m/s and exits with the turbulent flow velocity distribution given by u = umax(1 − r/R)1/7. If the pressure drop along the
A horizontal water jet impinges against a vertical flat plate at 30 ft/s and splashes off the sides in the vertical plane. If a horizontal force of 500 lbf is required to hold the plate against the
The water level in a tank is 70 ft above the ground. A hose is connected to the bottom of the tank, and the nozzle at the end of the hose is pointed straight up. The tank is at sea level, and the
Water is pumped from a lower reservoir to a higher reservoir by a pump that provides 23 kW of useful mechanical power to the water. The free surface of the upper reservoir is 57 m higher than the
A 78-percent-efficient 12-hp pump is pumping water from a lake to a nearby pool at a rate of 1.2 ft3/s through a constant- diameter pipe. The free surface of the pool is 32 ft above that of the lake.
Water flows at a rate of 0.040 m3/s in a horizontal pipe whose diameter is reduced from 15 cm to 8 cm by a reducer. If the pressure at the centerline is measured to be 480 kPa and 440 kPa before and
What is useful pump head? How is it related to the power input to the pump?
In cold climates, water pipes may freeze and burst if proper precautions are not taken. In such an occurrence, the exposed part of a pipe on the ground ruptures, and water shoots up to 55 m. Estimate
The water in a 25-m-deep reservoir is kept inside by a 90-m-wide wall whose cross section is an equilateral triangle, as shown in Fig. P11–47. Determine (a) the total force (hydrostatic +
The air velocity in a duct is measured by a Pitot-static probe connected to a differential pressure gage. If the air is at 13.4 psia absolute and 70°F and the reading of the differential pressure
An airplane is flying at an altitude of 10,500 m. Determine the gage pressure at the stagnation point on the nose of the plane if the speed of the plane is 450 km/h. How would you solve this problem
An air-standard cycle is executed within a closed piston–cylinder system and consists of three processes as follows:1-2 V = constant heat addition from 100 kPa and 27°C to 850
Air (cp = 1.005 kJ/kg·°C) is to be preheated by hot exhaust gases in a crossflow heat exchanger before it enters the furnace. Air enters the heat exchanger at 95 kPa and 20°C at a rate of 1.6
A mass of 25 lbm of helium undergoes a process from an initial state of 50 ft3/lbm and 60°F to a final state of 20 ft3/ lbm and 240°F. Determine the entropy change of helium during this process,
A cone floats in the glycerin (SG = 1.26), as shown in the figure. Find the mass of the cone. SG= 1.26/ FIGURE P11-37 R- h = 30 cm 60 cm
One of the common procedures in fitness programs is to determine the fat-to-muscle ratio of the body. This is based on the principle that the muscle tissue is denser than the fat tissue, and, thus,
It is estimated that 90 percent of an iceberg’s volume is below the surface, while only 10 percent is visible above the surface. For seawater with a density of 1025 kg/m3, estimate the density of
A room in the lower level of a cruise ship has a 40-cm-diameter circular window. If the midpoint of the window is 2 m below the water surface, determine the hydrostatic force acting on the window,
A fluid between two very long parallel plates is heated in a way that its viscosity decreases linearly from 0.90 Pa⋅s at the lower plate to 0.50 Pa⋅s at the upper plate. The spacing between the
A 200-kg granite rock (ρ = 2700 kg/m3) is dropped into a lake. A man dives in and tries to lift the rock. Determine how much force the man needs to apply to lift it from the bottom of the lake. Do
The analysis of a propeller that operates in water at 60°F shows that the pressure at the tips of the propeller drops to 0.1 psia at high speeds. Determine if there is a danger of cavitation for
Contrary to what you might expect, a solid steel ball can float on water due to the surface tension effect. Determine the maximum diameter of a steel ball that would float on water at 10°C. What
A 0.018-in-diameter glass tube is inserted into mercury, which makes a contact angle of 140° with glass. Determine the capillary drop of mercury in the tube at 68°F.
The surface tension of a liquid is to be measured using a liquid film suspended on a U-shaped wire frame with an 8 cm-long movable side. If the force needed to move the wire is 0.030 N, determine the
A 50-cm × 30-cm × 20-cm block weighing 150 N is to be moved at a constant velocity of 1.10 m/s on an inclined surface with a friction coefficient of 0.27. (a) Determine the force F that needs
A 1.6-mm-diameter tube is inserted into an unknown liquid whose density is 960 kg/m3, and it is observed that the liquid rises 5 mm in the tube, making a contact angle of 15°. Determine the surface
The clutch system shown in Fig. P10–24 is used to transmit torque through a 2-mm-thick oil film with μ = 0.38 N⋅s/m2 between two identical 30-cm-diameter disks. When the driving shaft rotates at
The viscosity of a fluid is to be measured by a viscometer constructed of two 75-cm-long concentric cylinders. The outer diameter of the inner cylinder is 15 cm, and the gap between the two cylinders
What is a Newtonian fluid? Is water a Newtonian fluid?
The pressure on the suction side of pumps is typically low, and the surfaces on that side of the pump are susceptible to cavitation, especially at high fluid temperatures. If the minimum pressure on
What is cavitation? What causes it?
What is the no-slip condition? What causes it?
A heat pump that operates on the ideal vapor-compression cycle with refrigerant-134a is used to heat a house and maintain it at 75°F by using underground water at 50°F as the heat source. The house
A gas turbine for an automobile is designed with a regenerator. Air enters the compressor of this engine at 100 kPa and 30°C. The compressor pressure ratio is 8; the maximum cycle temperature is
A simple ideal Rankine cycle which uses water as the working fluid operates its condenser at 40°C and its boiler at 250°C. Calculate the work produced by the turbine, the heat supplied in the
What is the difference between spark-ignition and compression- ignition engines?
What are the air-standard assumptions?
In order to cool 1 ton of water at 20°C in an insulated tank, a person pours 140 kg of ice at –5°C into the water. Determine (a) The final equilibrium temperature in the tank (b) The
A steam turbine is equipped to bleed 6 percent of the inlet steam for feedwater heating. It is operated with 4 MPa and 350°C steam at the inlet, a bleed pressure of 800 kPa, and an exhaust pressure
Air is expanded in an adiabatic turbine of 90 percent isentropic efficiency from an inlet state of 2800 kPa and 400°C to an outlet pressure of 100 kPa. Calculate the outlet temperature of air, the
A piston–cylinder device contains steam that undergoes a reversible thermodynamic cycle. Initially the steam is at 400 kPa and 350°C with a volume of 0.5 m3. The steam is first expanded
The inner and outer surfaces of a 4-m × 10-m brick wall of thickness 20 cm are maintained at temperatures of 16°C and 4°C, respectively. If the rate of heat transfer through the wall is 1800 W,
Stainless-steel ball bearings (ρ = 8085 kg/m3 and cp = 0.480 kJ/kg·°C) having a diameter of 1.8 cm are to be quenched in water at a rate of 1100 per minute. The balls leave the oven at a uniform
Steam is to be condensed in the condenser of a steam power plant at a temperature of 60°C with cooling water from a nearby lake, which enters the tubes of the condenser at 18°C at a rate of 75 kg/s
The exhaust nozzle of a jet engine expands air at 300 kPa and 180°C adiabatically to 100 kPa. Determine the air velocity at the exit when the inlet velocity is low and the nozzle isentropic
Air is compressed in a piston–cylinder device from 90 kPa and 20°C to 600 kPa in a reversible isothermal process. Determine (a) The entropy change of air (b) The work done.
A 25-kg iron block initially at 280°C is quenched in an insulated tank that contains 100 kg of water at 18°C. Assuming the water that vaporizes during the process condenses back in the tank,
An insulated piston–cylinder device contains 5 L of saturated liquid water at a constant pressure of 150 kPa. An electric resistance heater inside the cylinder is now turned on, and 1700 kJ of

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