Questions and Answers of Thermodynamics An Engineering Approach

A mixture of 1 mol of H2 and 1 mol of Ar is heated at a constant pressure of 1 atm until 10 percent of H2 dissociates into monatomic hydrogen (H). Determine the final temperature of the mixture.
In your own words, write a summary of the differences between incompressible flow, subsonic flow, and supersonic flow.
Assuming you have a thermometer and a device to measure the speed of sound in a gas, explain how you can determine the mole fraction of helium in a mixture of helium gas and air.
Find out if there is a supersonic wind tunnel on your campus. If there is, obtain the dimensions of the wind tunnel and the temperatures and pressures as well as the Mach number at several locations
Argon gas is approaching a converging–diverging nozzle with a low velocity at 20°C and 150 kPa, and it leaves the nozzle at a supersonic velocity. If the cross-sectional area of the throat is
Air is flowing in a wind tunnel at 12°C and 66 kPa at a velocity of 190 m/s. The Mach number of the flow is(a) 0.56(b) 0.65(c) 0.73(d) 0.87(e) 1.7
Air is flowing in a wind tunnel at 25°C, 95 kPa, and 250 m/s. The stagnation pressure at the location of a probe inserted into the flow section is(a) 184 kPa(b) 96 kPa(c) 161 kPa(d) 122 kPa(e) 135
Air flows through a converging–diverging nozzle in which the exit area is 2.896 times the throat area. Upstream of the nozzle entrance, the velocity is negligibly small and the pressure and
Air is cooled as it flows through a 30-cm-diameter duct. The inlet conditions are Ma1 = 1.2, T01 = 350 K, and P01 = 240 kPa and the exit Mach number is Ma2 = 2.0. Disregarding frictional effects,
Helium enters a nozzle at 0.5 MPa, 600 K, and a velocity of 120 m/s. Assuming isentropic flow, determine the pressure and temperature of helium at a location where the velocity equals the speed of
Nitrogen enters a steady-flow heat exchanger at 150 kPa, 10°C, and 100 m/s, and it receives heat in the amount of 150 kJ/kg as it flows through it. The nitrogen leaves the heat exchanger at 100 kPa
The thrust developed by the engine of a Boeing 777 is about 380 kN. Assuming choked flow in the nozzles, determine the mass flow rate of air through the nozzle. Take the ambient conditions to be 215
Steam enters a converging nozzle at 5.0 MPa and 400°C with a negligible velocity, and it exits at 3.0 MPa. For a nozzle exit area of 75 cm2, determine the exit velocity, mass flow rate, and exit
Air flows with negligible friction through a 6-indiameter duct at a rate of 9 lbm/s. The temperature and pressure at the inlet are T1 = 800 R and P1 = 30 psia, and the Mach number at the exit is Ma2
Reconsider Prob. 17–90. Calculate the entropy changes of air and helium across the normal shock.Data From Reconsider Prob. 17–90:Air flowing steadily in a nozzle experiences a normal shock at a
Air flowing at 40 kPa, 210 K, and a Mach number of 3.4 impinges on a two-dimensional wedge of half-angle 8°. Determine the two possible oblique shock angles, βweak and βstrong, that could be
Air at 12 psia, 30°F, and a Mach number of 2.0 is forced to turn upward by a ramp that makes an 8° angle off the flow direction. As a result, a weak oblique shock forms. Determine the wave angle,
Air enters a converging–diverging nozzle with low velocity at 2.4 MPa and 120°C. If the exit area of the nozzle is 3.5 times the throat area, what must the back pressure be to produce a normal
Quiescent carbon dioxide at 900 kPa and 500 K is accelerated isentropically to a Mach number of 0.6. Determine the temperature and pressure of the carbon dioxide after acceleration.
The Airbus A-340 passenger plane has a maximum takeoff weight of about 260,000 kg, a length of 64 m, a wingspan of 60 m, a maximum cruising speed of 945 km/h, a seating capacity of 271 passengers, a
Repeat Prob. 17–24 for helium gas.Data Form Repeat Prob. 17–24:Air expands isentropically from 2.2 MPa and 77°C to 0.4 MPa. Calculate the ratio of the initial to the final speed of sound.
Carbon dioxide enters an adiabatic nozzle at 800 K with a velocity of 50 m/s and leaves at 400 K. Assuming constant specific heats at room temperature, determine the Mach number(a) At the inlet(b) At
Products of combustion enter a gas turbine with a stagnation pressure of 0.90 MPa and a stagnation temperature of 840°C, and they expand to a stagnation pressure of 100 kPa. Taking k = 1.33 and R =
Air flows through a device such that the stagnation pressure is 0.4 MPa, the stagnation temperature is 400°C, and the velocity is 520 m/s. Determine the static pressure and temperature of the air at
What is dynamic temperature?
To protect the atmosphere, it has been suggested that hydrogen be used as a fuel in aircraft that fly at high elevations. This would avoid the formation of carbon dioxide and other carbon-based
Automobiles are major emitters of air pollutants such as NOx, CO, and hydrocarbons (HC). Find out the legal limits of these pollutants in your area, and estimate the total amount of each pollutant,
One means of producing liquid oxygen from atmospheric air is to take advantage of the phase-equilibrium properties of oxygen–nitrogen mixtures. This system is illustrated in Fig. P16–122. In this
An article that appeared in the Reno Gazette-Journal on May 18, 1992, quoted an inventor as saying that he had turned water into motor vehicle fuel in a breakthrough that would increase engine
An engineer suggested that high-temperature disassociation of water be used to produce a hydrogen fuel. A reactor–separator has been designed that can accommodate temperatures as high as 4000 K and
A gas turbine (Brayton cycle) at a natural gas pipeline pumping station uses natural gas (methane) as its fuel. Air is drawn into the turbine at 101 kPa and 25°C; and the pressure ratio of the
Repeat Prob. 16–100 for a relative humidity of 25 percent.Data From Q#100:Consider a glass of water in a room at 25°C and 100 kPa. If the relative humidity in the room is 70 percent and the water
Reconsider Prob. 16–95. What is the equilibrium mole fraction of the water vapor?Data From Q#95:Determine the equilibrium constant for the reaction CH4 + 2O2 ⇌ CO2 + 2H2O when the reaction occurs
One lbmol of refrigerant-134a is mixed with 1 lbmol of water in a closed container which is maintained at 14.7 psia and 77°F. Determine the mole fraction of the refrigerant-134a in the liquid phase
At what temperature will the gaseous phase of an oxygen– nitrogen mixture at 100 kPa have a nitrogen mole fraction of 30 percent? What is the mass fraction of the oxygen in the liquid phase at this
A liquid-vapor mixture of refrigerant-134a is at –10°C with a quality of 40 percent. Determine the value of the Gibbs function, in kJ/kg, when the two phases are in equilibrium. R-134a -10°C x=
Calculate the value of the Gibbs function for saturated refrigerant-134a at 0°C as a saturated liquid, saturated vapor, and a mixture of liquid and vapor with a quality of 30 percent. Demonstrate
Will a fuel burn more completely at 2000 or 2500 K?
What is the importance of the van’t Hoff equation?
A mixture of 2 mol of CO2 and 1 mol of O2 is heated to 2800 K at a pressure of 4 atm. Determine the equilibrium composition of the mixture, assuming that only CO2, CO, O2, and O are present.
A mixture of ideal gases is blended in a rigid vessel that is initially evacuated and is maintained at a constant temperature of 20°C. First, nitrogen is added until the pressure is 110 kPa, next
A mixture of ideal gases is blended in a rigid vessel that is initially evacuated and is maintained at a constant temperature of 20°C. First, nitrogen is added until the pressure is 110 kPa, next
Consider the reaction 2H2O ⇌ 2H2 + O2 at 4000 K and 10 kPa. How will the amount of hydrogen gas produced change if inert nitrogen is mixed with the water vapor such that the original mole
Consider the reaction 2H2O ⇌ 2H2 + O2 at 4000 K and 10 kPa. Will the amount of hydrogen gas produced be increased when the reaction occurs at 100 kPa rather than 10 kPa?
An inventor claims she can produce hydrogen gas by the reversible reaction 2H2O ⇌ H2 + O2. Determine the mole fractions of the hydrogen and oxygen produced when this reaction occurs at 4000 K and
Use the Gibbs function to determine the equilibrium constant of the H2O ⇌ H2 + 1/2 O2 reaction at(a) 1440 R(b) 3960 R.How do these compare to the equilibrium constants of Table A–28? TABLE A-28
A mixture of ideal gases consists of the following gases by mole fraction: 10 percent CO2, 60 percent H2O, and 30 percent CO. Determine the Gibbs function of the CO in this mixture when the mixture
At what temperature will oxygen be 15 percent disassociated at(a) 3 psia(b) 100 psia?
Determine the temperature at which 10 percent of diatomic hydrogen (H2) dissociates into monatomic hydrogen (H) at a pressure of 10 atm. Initial Equilibrium composition 10 atm 0.9H2 composition 1
The equilibrium constant for C + 1/2 O2 CO2 reaction at 100 kPa and 1600 K is Kp. Use this information to find the equilibrium constant for the following reactions at 1600 K.(a) C + 1/2 O2 ⇌ CO
An electric utility uses a Pennsylvania coal that has an ultimate analysis (by mass) of 84.36 percent C, 1.89 percent H2, 4.40 percent O2, 0.63 percent N2, 0.89 percent S, and 7.83 percent ash (non
What is oxygenated fuel? How would the heating value of oxygenated fuels compare to those of comparable hydrocarbon fuels on a unit-mass basis? Why is the use of oxygenated fuels mandated in some
A promising method of power generation by direct energy conversion is through the use of magnetohydrodynamic (MHD) generators. Write an essay on the current status of MHD generators. Explain their
One kmol of methane (CH4) is burned with an unknown amount of air during a combustion process. If the combustion is complete and there is 1 kmol of free O2 in the products, the air–fuel mass ratio
Benzene gas (C6H6) is burned with 90 percent theoretical air during a steady-flow combustion process. The mole fraction of the CO in the products is(a) 1.7%(b) 2.3%(c) 3.6%(d) 4.4%(e) 14.3%
Propane (C3H8) is burned with 125 percent theoretical air. The air–fuel mass ratio for this combustion process is(a) 12.3(b) 15.7(c) 19.5(d) 22.1(e) 23.4
Methane (CH4) is burned with 100 percent excess air, with 10 percent of the carbon forming carbon monoxide. Determine the maximum work that can be produced, in Btu/lbm fuel, when the air, fuel, and
Repeat Prob. 15–109 if 100 percent excess air is used for the combustion.Data From Q#109:n-Octane [C8H18(g)] is burned with the stoichiometric amount of air. Determine the maximum work that can be
n-Octane [C8H18(g)] is burned with the stoichiometric amount of air. Determine the maximum work that can be produced, in kJ/kg fuel, when the air, fuel, and products are all at 25°C and 1 atm.
Calculate the higher and lower heating values of gaseous methane fuel (CH4). Compare your results with the values in Table A–27.
n-Butane (C4H10) is burned with the stoichiometric amount of air in a cook stove. The products of combustion are at 1 atm pressure and 40°C. What fraction of the water in these products is liquid?
A coal from Colorado which has an ultimate analysis (by mass) of 79.61 percent C, 4.66 percent H2, 4.76 percent O2, 1.83 percent N2, 0.52 percent S, and 8.62 percent ash (non combustibles) is burned
Reconsider Prob. 15–88. The automobile engine is to be converted to natural gas (methane, CH4) fuel. Assuming that all factors remain the same, what is the maximum work that can be produced by the
n-Octane [C8H18(l)] is burned in an automobile engine with 200 percent excess air. Air enters this engine at 1 atm and 25°C. Liquid fuel at 25°C is mixed with this air before combustion. The
What does the Gibbs function of formation g̅°f of a compound represent?
Reconsider Prob. 15–82. The combustion products are expanded in an isentropic turbine to 140 kPa. Calculate the work produced by this turbine in kJ/kg fuel.Data From Q#82:A large railroad has
A large railroad has experimented with burning powdered coal in a gas turbine combustor. Fifty percent excess air was introduced to the combustor at 1380 kPa and 127°C while the powdered coal was
Methane (CH4) is burned with 300 percent excess air in an adiabatic constant-volume container. Initially, air and methane are at 1 atm and 25°C. Assuming complete combustion, determine the final
Ethyl alcohol [C2H5OH(g)] is burned with 200 percent excess air in an adiabatic, constant-volume container. Initially, air and ethyl alcohol are at 100 kPa and 25°C. Assuming complete combustion,
A fuel at 25°C is burned in a well-insulated steady flow combustion chamber with air that is also at 25°C. Under what conditions will the adiabatic flame temperature of the combustion process be a
A constant-volume tank contains a mixture of 1 lbmol of benzene (C6H6) gas and 60 percent excess air at 77°F and 1 atm. The contents of the tank are now ignited, and all the hydrogen in the fuel
Gaseous propane (C3H8) is burned in a steady-flow, constant-pressure process at 100 kPa with 200 percent theoretical air. During the combustion process, 90 percent of the carbon in the fuel is
Propane fuel (C3H8) is burned in a space heater with 50 percent excess air. The fuel and air enter this heater steadily at 1 atm and 17°C, while the combustion products leave at 1 atm and 97°C.
Calculate the HHV and LHV of gaseous n-octane fuel (C8H18). Compare your results with the values in Table A–27. TABLE A-27 Properties of some common fuels and hydrocarbons Higher heating value,
Repeat Prob. 15–46 for liquid octane (C8H18).Data From Q#46:Determine the enthalpy of combustion of methane (CH4) at 25°C and 1 atm, using the enthalpy of formation data from Table A–26.
Repeat Prob. 15–46 for gaseous ethane (C2H6).Data From Q#46:Determine the enthalpy of combustion of methane (CH4) at 25°C and 1 atm, using the enthalpy of formation data from Table A–26.
Calculate the higher and lower heating values of a coal from Utah which has an ultimate analysis (by mass) of 61.40 percent C, 5.79 percent H2, 25.31 percent O2, 1.09 percent N2, 1.41 percent S, and
Reconsider Prob. 15–31. Using appropriate software, study the effects of varying the percentages of CH4, H2, and N2 making up the fuel and the product gas temperature in the range 5 to 85°C.Data
Does the enthalpy of formation of a substance change with temperature?
Determine the fuel–air ratio when coal from Colorado, which has an ultimate analysis (by mass) as 79.61 percent C, 4.66 percent H2, 4.76 percent O2, 1.83 percent N2, 0.52 percent S, and 8.62
The fuel mixer in a natural gas burner mixes methane (CH4) with air to form a combustible mixture at the outlet. Determine the mass flow rates at the two inlets needed to produce 0.5 kg/s of an ideal
Methyl alcohol (CH3OH) is burned with 50 percent excess air. The combustion is incomplete with 10 percent of the carbon in the fuel forming carbon monoxide. Calculate the mole fraction of carbon
Ethane (C2H6) is burned with 20 percent excess air during a combustion process. Assuming complete combustion and a total pressure of 100 kPa, determine(a) The air–fuel ratio(b) The dew-point
Methyl alcohol (CH3OH) is burned with the stoichiometric amount of air. Calculate the mole fractions of each of the products, and the apparent molar mass of the product gas. Also, calculate the mass
Propane fuel (C3H8) is burned with 30 percent excess air. Determine the mole fractions of each of the products. Also, calculate the mass of water in the products per unit mass of the fuel and the
Consider a fuel that is burned with (a) 130 percent theoretical air (b) 70 percent excess air. In which case is the fuel burned with more air?
Is the air–fuel ratio expressed on a mole basis identical to the air–fuel ratio expressed on a mass basis?
What are the approximate chemical compositions of gasoline, diesel fuel, and natural gas?
A hurricane is a large heat engine driven by the exchange of water with humid air. Evaporation of ocean water occurs as the air approaches the eye of the storm, and condensation occurs as rain near
The operation of a cooling tower is governed by the principles of fluid mechanics, heat transfer, and mass transfer, as well as thermodynamics. The laws of thermodynamics do place bounds on the
The condensation and even freezing of moisture in building walls without effective vapor retarders are of real concern in cold climates as they undermine the effectiveness of the insulation.
The daily change in the temperature of the atmosphere tends to be smaller in locations where the relative humidity is high. Demonstrate why this occurs by calculating the change in the temperature of
The air-conditioning needs of a large building can be met by a single central system or by several individual window units. Considering that both approaches are commonly used in practice, the right
Identify the major sources of heat gain in your house in summer, and propose ways of minimizing them and thus reducing the cooling load.
Air is cooled and dehumidified as it flows over the coils of a refrigeration system at 100 kPa from 30°C and a humidity ratio of 0.023 kg/kg dry air to 15°C and a humidity ratio of 0.015 kg/kg dry
The air in a house is at 25°C and 65 percent relative humidity. Now the air is cooled at constant pressure. The temperature at which the moisture in the air will start condensing is(a) 7.4°C(b)
A room contains 65 kg of dry air and 0.43 kg of water vapor at 25°C and 90 kPa total pressure. The relative humidity of air in the room is(a) 29.9%(b) 35.2%(c) 41.5%(d) 60.0%(e) 66.2%
An automobile air conditioner uses refrigerant-134a as the cooling fluid. The evaporator operates at 100 kPa gage and the condenser operates at 1.5 MPa gage. The compressor requires a power input of
Reconsider Prob. 14–128E. The relative humidity of the air in a home is to be restored to 60 percent by evaporating 60°F water into the air. How much heat, in Btu, is required to do this in a home
A typical winter day in Fairbanks, Alaska, has a pressure of 1 atm, a temperature of 32°F, and a relative humidity of 60 percent. What is the relative humidity inside a home where this air has been

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