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physics
thermodynamics

Thermodynamics An Engineering Approach 8th edition Yunus A. Cengel, Michael A. Boles - Solutions

Calculate the absolute pressure, P1, of the manometer shown in Fig. P1 - 78 in kPa. The local atmospheric pressure is 758 mmHg.
Consider the manometer in Fig. P1-78. If the specific weight of fluid A is 100 kN/m3, what is the absolute pressure, in kPa, indicated by the manometer when the local atmospheric pressure is 90 kPa?
A mass of 5 kg of saturated water vapor at 300 kPa is heated at constant pressure until the temperature reaches 200oC. Compute the work done by the steam during this procedure.
Consider the manometer in Fig. P1-78. If the specific weight of fluid B is 20 kN/m3, what is the absolute pressure, in kPa, indicated by the manometer when the local atmospheric pressure is 720 mmHg?
Consider the system shown in Fig. P1-81. If a change of 0.7 kPa in the pressure of air causes the brine-mercury interface in the right column to drop by 5 mm in the brine level in the right column while the pressure in the brine pipe remains constant, determine the ratio of A2/A1.
What is the value of the engineering software packages in (a) engineering education and (b) engineering practice?
Determine a positive real root of this equation using EES:2x3- 10x0.5 - 3x = - 3
Solve this system of two equations with two unknowns using EES: x3 - y2 = 7.75 3xy + y = 3.5
Solve this system of three equations with three unknowns using EES: x2y - z = 1 x - 3y0.5 + xz = - 2 x + y - z = 2
Solve this system of three equations with three unknowns using EES: 2x - y + z = 7 3x2 + 3y = z + 3 xy + 2z = 4
Specific heat is defined as the amount of energy needed to increase the temperature of a unit mass of a substance by one degree. The specific heat of water at room temperature is 4.18 kJ/kg·°C in SI unit system. Using the unit conversion function capability of EES, express the specific heat of
The weight of bodies may change somewhat from one location to another as a result of the variation of the gravitational acceleration g with elevation. Accounting for this variation using the relation in Prob. 1-8, determine the weight of an 80-kg person at sea level (z = 0), in Denver (z = 1610 m),
A man goes to a traditional market to buy a steak for dinner. He finds a 12-oz steak (1 lbm 5 16 oz) for $5.50. He then goes to the adjacent international market and finds a 300-g steak of identical quality for $5.20. Which steak is the better buy?
1-m3 of saturated liquid water at 200°C is expanded isothermally in a closed system until its quality is 80 percent. Determine the total work produced by this expansion, in kJ.
What is the weight of a 1-kg substance in N, kN, kg·m/s2, kgf, lbm·ft/s2, and lbf?
A hydraulic lift is to be used to lift a 2500 kg weight by putting a weight of 25 kg on a piston with a diameter of 10 cm. Determine the diameter of the piston on which the weight is to be placed.
The efficiency of a refrigerator increases by 3 percent for each °C rise in the minimum temperature in the device. What is the increase in the efficiency for each (a) K, (b) °F, and (c) R rise in temperature?
Hyperthermia of 5°C (i.e., 5°C rise above the normal body temperature) is considered fatal. Express this fatal level of hyperthermia in (a) K, (b) °F, and (c) R.
A house is losing heat at a rate of 1800 kJ/h per °C temperature difference between the indoor and the outdoor temperatures. Express the rate of heat loss from this house per (a) K, (b) °F, and (c) R difference between the indoor and the outdoor temperature.
The average temperature of the atmosphere in the world is approximated as a function of altitude by the relation Tatm = 288.15 - 6.5z where Tatm is the temperature of the atmosphere in K and z is the altitude in km with z = 0 at sea level. Determine the average temperature of the atmosphere
Joe Smith, an old-fashioned engineering student, believes that the boiling point of water is best suited for use as the reference point on temperature scales. Unhappy that the boiling point corresponds to some odd number in the current absolute temperature scales, he has proposed a new absolute
It is well-known that cold air feels much colder in windy weather than what the thermometer reading indicates because of the "chilling effect" of the wind. This effect is due to the increase in the convection heat transfer coefficient with increasing air velocities. The equivalent wind chill
Reconsider Prob. 1-97E. Using EES (or other) software, plot the equivalent wind chill temperatures in °F as a function of wind velocity in the range of 4 to 40 mph for the ambient temperatures of 20, 40, and 60°F. Discuss the results.
A vertical piston-cylinder device contains a gas at a pressure of 100 kPa. The piston has a mass of 5 kg and a diameter of 12 cm. Pressure of the gas is to be increased by placing some weights on the piston. Determine the local atmospheric pressure and the mass of the weights that will double the
What is total energy? Identify the different forms of energy that constitute the total energy.
A person gets into an elevator at the lobby level of a hotel together with his 30-kg suitcase, and gets out at the 10th floor 35 m above. Determine the amount of energy consumed by the motor of the elevator that is now stored in the suitcase.
Reconsider Prob. 2 - 99. Using EES (or other) software, investigate the effect of the convection heat transfer coefficient and surface emissivity on the heat transfer rate from the ball. Let the heat transfer coefficient vary from 5 to 30 W/m2·8C. Plot the rate of heat transfer against the
A 1000-W iron is left on the ironing board with its base exposed to the air at 23oC. The convection heat transfer coefficient between the base surface and the surrounding air is 20 W/m2·8C. If the base has an emissivity of 0.4 and a surface area of 0.02 m2, determine the temperature of the
A 7-cm-external-diameter, 18-m-long hot-water pipe at 808C is losing heat to the surrounding air at 5oC by natural convection with a heat transfer coefficient of 25W/m2·oC. Determine the rate of heat loss from the pipe by natural convection, in kW.
A thin metal plate is insulated on the back and exposed to solar radiation on the front surface. The exposed surface of the plate has an absorptivity of 0.8 for solar radiation. If solar radiation is incident on the plate at a rate of 450 W/m2 and the surrounding air temperature is 25oC, determine
Reconsider Prob. 2 - 103. Using EES (or other) software, investigate the effect of the convection heat transfer coefficient on the surface temperature of the plate. Let the heat transfer coefficient vary from 10 to 90 W/m2·oC. Plot the surface temperature against the convection heat transfer
The outer surface of a spacecraft in space has an emissivity of 0.6 and an absorptivity of 0.2 for solar radiation. If solar radiation is incident on the spacecraft at a rate of 1000 W/m2, determine the surface temperature of the spacecraft when the radiation emitted equals the solar energy
Reconsider Prob. 2-105. Using EES (or other) software, investigate the effect of the surface emissivity and absorptivity of the spacecraft on the equilibrium surface temperature. Plot the surface temperature against emissivity for solar absorptivities of 0.1, 0.5, 0.8, and 1, and discuss the results
A hollow spherical iron container whose outer diameter is 40 cm and thickness is 0.4 cm is filled with iced water at 08C. If the outer surface temperature is 38C, determine the approximate rate of heat loss from the sphere, and the rate at which ice melts in the container.
Consider a vertical elevator whose cabin has a total mass of 800 kg when fully loaded and 150 kg when empty. The weight of the elevator cabin is partially balanced by a 400-kg counterweight that is connected to the top of the cabin by cables that pass through a pulley located on top of the elevator
Consider a homeowner who is replacing his 25-yearold natural gas furnace that has an efficiency of 55 percent. The homeowner is considering a conventional furnace that has an efficiency of 82 percent and costs $1600 and a highefficiency furnace that has an efficiency of 95 percent and costs $2700.
Electric power is to be generated by installing a hydraulic turbine-generator at a site 120 m below the free surface of a large water reservoir that can supply water at a rate of 2400 kg/s steadily. Determine the power generation potential.
The energy contents, unit costs, and typical conversion efficiencies of various energy sources for use in water heaters are given as follows: 1025 Btu/ft3, $0.012/ft3, and 85 percent for natural gas; 138,700 Btu/gal, $2.2/gal, and 75 percent for heating oil; and 1 kWh/kWh, $0.11/kWh, and 90 percent
A homeowner is considering these heating systems for heating his house: Electric resistance heating with $0.12/ kWh and 1 kWh 5 3600 kJ, gas heating with $1.24/therm and 1 therm 5 105,500 kJ, and oil heating with $2.3/gal and 1 gal of oil 5 138,500 kJ. Assuming efficiencies of 100 percent for the
The U.S. Department of Energy estimates that 570,000 barrels of oil would be saved per day if every household in the United States lowered the thermostat setting in winter by 6 ºF (3.3ºC). Assuming the average heating season to be 180 days and the cost of oil to be $110/barrel, determine how much
The U.S. Department of Energy estimates that up to 10 percent of the energy use of a house can be saved by caulking and weatherstripping doors and windows to reduce air leaks at a cost of about $90 for materials for an average home with 12 windows and 2 doors. Caulking and weatherstripping every
The force required to compress the gas in a gas spring a distance x is given by F = constant/xk where the constant is determined by the geometry of this device and k is determined by the gas used in the device. One such device has a constant of 200 lbf·in1.4 and k 5 1.4. Determine the work, in
A man weighing 180 lbf pushes a block weighing 100 lbf along a horizontal plane. The dynamic coefficient of friction between the block and plane is 0.2. Assuming that the block is moving at constant speed, calculate the work required to move the block a distance of 100 ft considering (a) The man
A diesel engine with an engine volume of 4.0 L and an engine speed of 2500 rpm operates on an air-fuel ratio of 18 kg air/kg fuel. The engine uses light diesel fuel that contains 750 ppm (parts per million) of sulfur by mass. All of this sulfur is exhausted to the environment where the sulfur is
Leaded gasoline contains lead that ends up in the engine exhaust. Lead is a very toxic engine emission. The use of leaded gasoline in the United States has been unlawful for most vehicles since the 1980s. However, leaded gasoline is still used in some parts of the world. Consider a city with 70,000
Consider a TV set that consumes 120 W of electric power when it is on and is kept on for an average of 6 hours per day. For a unit electricity cost of 12 cents per kWh, determine the cost of electricity this TV consumes per month (30 days).
Water is pumped from a 200-ft-deep well into a 100-ft-high storage tank. Determine the power, in kW, that would be required to pump 200 gallons per minute.
At a certain location, wind is blowing steadily at 10 m/s. Determine the mechanical energy of air per unit mass and the power generation potential of a wind turbine with 60-m diameter blades at that location. Take the air density to be 1.25 kg/m3.
A grist mill of the 1800s employed a water wheel that was 14 m high; 320 liters per minute of water flowed on to the wheel near the top. How much power, in kW, could this water wheel have produced?
Windmills slow the air and cause it to fill a larger channel as it passes through the blades. Consider a circular windmill with a 7-m-diameter rotor in a 8 m/s wind on a day when the atmospheric pressure is 100 kPa and the temperature is 208C. The wind speed behind the windmill is measured at 6.5
In a hydroelectric power plant, 65 m3/s of water flows from an elevation of 90 m to a turbine, where electric power is generated. The overall efficiency of the turbine - generator is 84 percent. Disregarding frictional losses in piping, estimate the electric power output of this plant.
The demand for electric power is usually much higher during the day than it is at night, and utility companies often sell power at night at much lower prices to encourage consumers to use the available power generation capacity and to avoid building new expensive power plants that will be used only
The pump of a water distribution system is powered by a 15-kW electric motor whose efficiency is 90 percent. The water flow rate through the pump is 50 L/s. The diameters of the inlet and outlet pipes are the same, and the elevation difference across the pump is negligible. If the pressures at the
On a hot summer day, the air in a well-sealed room is circulated by a 0.50-hp fan driven by a 65 percent efficient motor. (Note that the motor delivers 0.50 hp of net shaft power to the fan.) The rate of energy supply from the fanmotor assembly to the room is (a) 0.769 kJ/s (b) 0.325 kJ/s (c)
A fan is to accelerate quiescent air to a velocity to 12 m/s at a rate of 3 m3/s. If the density of air is 1.15 kg/m3, the minimum power that must be supplied to the fan is (a) 248 W (b) 72 W (c) 497 W (d) 216 W (e) 162 W
A 2-kW electric resistance heater in a room is turned on and kept on for 50 min. The amount of energy transferred to the room by the heater is (a) 2 kJ (b) 100 kJ (c) 3000 kJ (d) 6000 kJ (e) 12,000 kJ
A 900-kg car cruising at a constant speed of 60 km/s is to accelerate to 100 km/h in 4 s. The additional power needed to achieve this acceleration is (a) 56 kW (b) 222 kW (c) 2.5 kW (d) 62 kW (e) 90 kW
The elevator of a large building is to raise a net mass of 400 kg at a constant speed of 12 m/s using an electric motor. Minimum power rating of the motor should be (a) 0 kW (b) 4.8 kW (c) 47 kW (d) 12 kW (e) 36 kW
A water jet that leaves a nozzle at 60 m/s at a flow rate of 120 kg/s is to be used to generate power by striking the buckets located on the perimeter of a wheel. Determine the power generation potential of this water jet.
Electric power is to be generated in a hydroelectric power plant that receives water at a rate of 70 m3/s from an elevation of 65 m using a turbine-generator with an efficiency of 85 percent. When frictional losses in piping are disregarded, the electric power output of this plant is (a) 3.9 MW
Consider a refrigerator that consumes 320 W of electric power when it is running. If the refrigerator runs only one quarter of the time and the unit cost of electricity is $0.09/kWh, the electricity cost of this refrigerator per month (30 days) is (a) $3.56 (b) $5.18 (c) $8.54 (d) $9.28 (e)
A 2-kW pump is used to pump kerosene ( r 5 0.820 kg/L) from a tank on the ground to a tank at a higher elevation. Both tanks are open to the atmosphere, and the elevation difference between the free surfaces of the tanks is 30 m. The maximum volume flow rate of kerosene is (a) 8.3 L/s (b) 7.2 L/s
A glycerin pump is powered by a 5-kW electric motor. The pressure differential between the outlet and the inlet of the pump at full load is measured to be 211 kPa. If the flow ratethrough the pump is 18 L/s and the changes in elevation and the flow velocity across the pump are negligible, the
A 75-hp compressor in a facility that operates at full load for 2500 h a year is powered by an electric motor that has an efficiency of 93 percent. If the unit cost of electricity is $0.06/kWh, the annual electricity cost of this compressor is (a) $7802 (b) $9021 (c) $12,100 (d) $8389 (e)
A 10-cm high and 20-cm wide circuit board houses on its surface 100 closely spaced chips, each generating heat at a rate of 0.08 W and transferring it by convection to the surrounding air at 258C. Heat transfer from the back surface of the board is negligible. If the convection heat transfer
A 50-cm-long, 0.2-cm-diameter electric resistance wire submerged in water is used to determine the boiling heat transfer coefficient in water at 1 atm experimentally. The surface temperature of the wire is measured to be 1308C when a wattmeter indicates the electric power consumption to be 4.1 kW.
A 3-m2 hot black surface at 80oC is losing heat to the surrounding air at 25oC by convection with a convection heat transfer coefficient of 12 W/m2·oC, and by radiation to the surrounding surfaces at 158C. The total rate of heat loss from the surface is (a) 1987 W (b) 2239 W (c) 2348 W (d) 3451
Heat is transferred steadily through a 0.2-m thick 8 m 3 4 m wall at a rate of 2.4 kW. The inner and outer surface temperatures of the wall are measured to be 158C and 58C. The average thermal conductivity of the wall is (a) 0.002 W/m·8C (b) 0.75 W/m·8C (c) 1.0 W/m·8C (d) 1.5 W/m·8C (e) 3.0
The roof of an electrically heated house is 7-m long, 10-m wide, and 0.25-m thick. It is made of a flat layer of concrete whose thermal conductivity is 0.92 W/m·8C. During a certain winter night, the temperatures of the inner and outer surfaces of the roof are measured to be 158C and 48C,
Two sites are being considered for wind power generation. In the first site, the wind blows steadily at 7 m/s for 3000 hours per year, whereas in the second site the wind blows at 10 m/s for 1500 hours per year. Assuming the wind velocity is negligible at other times for simplicity, determine which
Consider a river flowing toward a lake at an average velocity of 3 m/s at a rate of 500 m3/s at a location 90 m above the lake surface. Determine the total mechanical energy of the river water per unit mass and the power generation potential of the entire river at that location.
Consider an automobile traveling at a constant speed along a road. Determine the direction of the heat and work interactions, taking the following as the system: (a) the car radiator, (b) the car engine, (c) the car wheels, (d ) the road, and (e) the air surrounding the car.
Consider an electric refrigerator located in a room. Determine the direction of the work and heat interactions (in or out) when the following are taken as the system:
An insulated room is heated by burning candles. Is this a heat or work interaction? Take the entire room, including the candles, as the system.
A small electrical motor produces 5 W of mechanical power. What is this power in (a) N, m, and s units; and (b) kg, m, and s units?
A model aircraft internal-combustion engine produces 10 W of power. How much power is this in (a) lbf·ft/s and (b) hp?
A man weighing 180 lbf is pushing a cart that weighs 100 lbf with its contents up a ramp that is inclined at an angle of 108 from the horizontal. Determine the work needed to move along this ramp a distance of 100 ft considering (a) the man and (b) the cart and its contents as the system. Express
A man weighing 180 lbf is pushing a cart that weighs 100 lbf with its contents up a ramp that is inclined at an angle of 108 from the horizontal. Determine the work needed to move along this ramp a distance of 100 ft considering (a) the man and (b) the cart and its contents as the system. Express
The force F required to compress a spring a distance x is given by F 2 F0 5 kx where k is the spring constant and F0 is the preload. Determine the work required to compress a spring whose spring constant is k 5 200 lbf/in a distance of one inch starting from its free length where F0 5 0 lbf.
Determine the energy required to accelerate a 1300-kg car from 10 to 60 km/h on an uphill road with a vertical rise of 40 m.
Determine the torque applied to the shaft of a car that transmits 450 hp and rotates at a rate of 3000 rpm.
A spherical soap bubble with a surface-tension of 0.005 lbf/ft is expanded from a diameter of 0.5 in to 3.0 in. How much work, in Btu, is required to expand this bubble?
Determine the work required to deflect a linear spring with a spring constant of 70 kN/m by 20 cm from its rest position.
A ski lift has a one-way length of 1 km and a vertical rise of 200 m. The chairs are spaced 20 m apart, and each chair can seat three people. The lift is operating at a steady speed of 10 km/h. Neglecting friction and air drag and assuming that the average mass of each loaded chair is 250 kg,
The engine of a 1500 - kg automobile has a power rating of 75 kW. Determine the timerequired to accelerate this car from rest to a speed of 100 km/h at full power on a level road. Is your answer realistic?
Determine the power required for a 1150-kg car to climb a 100-m-long uphill road with a slope of 308 (from horizontal) in 12 s (a) at a constant velocity, (b) from rest to a final velocity of 30 m/s, and (c) from 35 m/s to a final velocity of 5 m/s. Disregard friction, air drag, and rolling
Water is being heated in a closed pan on top of a range while being stirred by a paddle wheel. During the process, 30 kJ of heat is transferred to the water, and 5 kJ of heat is lost to the surrounding air. The paddle-wheel work amounts to 500 N ˆ™ m. Determine the final energy of the
What is mechanical energy? How does it differ from thermal energy? What are the forms of mechanical energy of a fluid stream?
A vertical piston-cylinder device contains water and is being heated on top of a range. During the process, 65 Btu of heat is transferred to the water, and heat losses from the side walls amount to 8 Btu. The piston rises as a result of evaporation, and 5 Btu of work is done by the vapor. Determine
At winter design conditions, a house is projected to lose heat at a rate of 60,000 Btu/h. The internal heat gain from people, lights, and appliances is estimated to be 6000 Btu/h. If this house is to be heated by electric resistance heaters, determine the required rated power of these heaters in kW
A water pump increases the water pressure from 15 psia to 70 psia. Determine the power input required, in hp, to pump 0.8 ft3/s of water. Does the water temperature at the inlet have any significant effect on the required flow ower?
A water pump that consumes 2 kW of electric power when operating is claimed to take in water from a lake and pump it to a pool whose free surface is 30 m above the free surface of the lake at a rate of 50 L/s. Determine if this claim is reasonable.
A classroom that normally contains 40 people is to be air-conditioned with window air conditioning units of 5-kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360 kJ/h. There are 10 lightbulbs in the room, each with a rating of 100 W. The rate of heat
A university campus has 200 classrooms and 400 faculty offices. The classrooms are equipped with 12 fluorescent tubes, each consuming 110 W, including the electricity used by the ballasts. The faculty offices, on average, have half as many tubes. The campus is open 240 days a year. The classrooms
The lighting requirements of an industrial facility are being met by 700 40-W standard fluorescent lamps. The lamps are close to completing their service life and are to be replaced by their 34-W high-efficiency counterparts that operate on the existing standard ballasts. The standard and
Consider a room that is initially at the outdoor temperature of 208C. The room contains a 40-W lightbulb, a 110-W TV set, a 300-W refrigerator, and a 1200-W iron. Assuming no heat transfer through the walls, determine the rate of increase of the energy content of the room when all of these electric
Consider a fan located in a 3 ft 3 × 3 ft square duct. Velocities at various points at the outlet are measured, and the average flow velocity is determined to be 22 ft/s. Taking the air density to 0.075lbm/ft3, estimate the minimum electric power consumption of the fan motor.
The 60-W fan of a central heating system is to circulate air through the ducts. The analysis of the flow shows that the fan needs to raise the pressure of air by 50 Pa to maintain flow. The fan is located in a horizontal flow section whose diameter is 30 cm at both the inlet and the outlet.
Natural gas, which is mostly methane CH4, is a fuel and a major energy source. Can we say the same about hydrogen gas, H2?
The driving force for fluid flow is the pressure difference, and a pump operates by raising the pressure of a fluid (by converting the mechanical shaft work to flow energy). A gasoline pump is measured to consume 3.8 kW of electric power when operating. If the pressure differential between the

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