Questions and Answers of Fundamentals Of Thermodynamics

Several applications of dehumidification do not rely on water condensation by cooling. A desiccant with a greater affinity to water can absorb water directly from the air accompanied by a heat
If the pressure is raised in an isothermal process, does h go up or down for a liquid or solid? What do you need to know if it is a gas phase?
Over what range of states are the various coefficients in Section 12.5 most useful?
For a liquid or a solid, is v more sensitive to T or P? How about an ideal gas?
Most equations of state are developed to cover which range of states?
Is an equation of state valid in the two-phase regions?
At which states are the departure terms for h and s small? What is Z there?
The departure functions for h and s as defined are always positive. What does that imply for the real-substance h and s values relative to ideal gas values?
What is the benefit of Kay’s rule versus a mixture equation of state?
A certain refrigerant vapor enters a steady-flow, constant-pressure condenser at 150 kPa, 70◦C, at a rate of 1.5 kg/s, and it exits as saturated liquid. Calculate the rate of heat transfer from the
Find the saturation pressure for the refrigerant R-410a at −80◦C, assuming it is higher than the triple-point temperature.
The Joule–Thomson coefficient μJ is a measure of the direction and magnitude of the temperature change with pressure in a throttling process. For any three properties x, y, z, use the mathematical
Evaluate the isothermal changes in internal energy, enthalpy, and entropy for an ideal gas.
Assume that a substance has uniform properties in all directions with V = Lx Ly Lz. Show that volume expansivity αp =3δT.
Use a truncated virial equation of state (EOS) that includes the term with B for carbon dioxide at 20◦C, 1 MPa for which B = −0.128 m3/kmol, and T(dB/dT) = 0.266 m3/kmol. Find the difference
Find changes in internal energy, enthalpy, and entropy for an isothermal process in a gas obeying the van der Waals EOS.
Consider the following EOS, expressed in terms of reduced pressure and temperature: Z = 1 + (Pr/14Tr)[1 − 6Tr −2]. What does this predict for the reduced Boyle temperature?
What is the Boyle temperature for this EOS with constants a and b: P = [RT/(v − b)] − a/v2T?
Develop expressions for isothermal changes in internal energy, enthalpy, and entropy for a gas obeying the Redlich–K wong EOS.
Oxygen in a rigid tank with 1 kg is at 160 K, 4 MPa. Find the volume of the tank by iterations using the Redlich–K wong EOS. Compare the result with the ideal gas law.
A flow of oxygen at 230 K, 5 MPa is throttled to 100 kPa in a steady-flow process. Find the exit temperature and the specific entropy generation using the Redlich–K wong EOS and ideal gas heat
How low should the pressure be so that nitrous oxide (N2O) gas at 278.6 K can be treated as an ideal gas with 5% accuracy or better?
Nitrous oxide (N2O) at 278.6 K is at a pressure so that it can be in a two-phase state. Find the generalized enthalpy departure for the two saturated states of liquid and vapor.
The new refrigerant R-152a is used in a refrigerator with an evaporator at −20◦C and a condenser at 30◦C. What are the high and low pressures in this cycle?
A 4-m3 storage tank contains ethane gas at 10 MPa, 100◦C. Using the Lee–Kesler EOS, find the mass of the ethane.
The ethane gas in the storage tank from the previous problem is cooled to 0◦C. Find the new pressure.
A geothermal power plant uses butane as saturated vapor at 80◦C into the turbine, and the condenser operates at 30◦C. Find the reversible specific turbine work.
Consider the following EOS, expressed in terms of reduced pressure and temperature: Z = 1 + (Pr/14Tr)[1 − 6Tr−2]. What does this predict for the enthalpy departure at Pr = 0.4 and Tr = 0.9? What
A very-low-temperature refrigerator uses neon. From the compressor, the neon at 1.5 MPa, 80 K goes through the condenser and comes out as saturated liquid at 40 K. Find the specific heat transfer
Find the heat of evaporation, hfg, for isobutane (Tc = 408.2 K, Pc = 3.65 MPa, M = 58.124) at 12.6◦C from the generalized charts and compare to the values in the CATT3 computerized tables.
A cylinder contains ethylene,C2H4, at 1.536MPa, −13◦C. It is now compressed isothermally in a reversible process to 5.12 MPa. Find the specific work and heat transfer.
A cylinder contains ethylene,C2H4, at 1.536MPa, −13◦C. It is now compressed in a reversible isobaric (constant-P) process to saturated liquid. Find the specific work and heat transfer.
An insulated piston/cylinder contains saturated vapor carbon dioxide at 0◦C and a volume of 20 L. The external force on the piston is slowly decreased, allowing the carbon dioxide to expand until
The refrigerant fluid R-123 (see Table A.2) is used in a refrigeration system that operates in the ideal refrigeration cycle, except that the compressor is neither reversible nor adiabatic. Saturated
A2-kg mixture of 50% argon and 50% nitrogen by mole is in a tank at 2 MPa, 180 K. How large is the volume using a model of (a) ideal gas and (b) Kay’s rule with generalized
A 2-kg mixture of 50% argon and 50% nitrogen by mole is in a tank at 2 MPa, 180 K. How large is the volume using a model of (a) Ideal gas and (b) Van der Waals’ EOS with a, b for a
A 2-kg mixture of 50% argon and 50% nitrogen by mole is in a tank at 2 MPa, 180 K. How large is the volume using a model of (a) Ideal gas and (b) The Redlich–Kwong EOS with a, b for a
Saturated liquid ethane at T1 = 14◦C is throttled into a steady-flow mixing chamber at the rate of 0.25 kmol/s. Argon gas at T2 = 25◦C, 800 kPa, enters the chamber at the rate 0.75 kmol/s. Heat
A piston/cylinder contains a gas mixture, 50% carbon dioxide and 50% ethane (C2H6) (mole basis), at 700 kPa, 35◦C, at which point the cylinder volume is 5 L. The mixture is now compressed to 5.5MPa
Find an expression for the change in Helmholtz function for a gas with an EOS as P(v − b) = RT.
Assume a Helmholtz equation aswhere C0, C1, and C2 are constants and T0 and ρ0 are reference values for temperature and density (see Eqs. 12.92–12.95). Find the properties P, u, and s from this
A new compound is used in an ideal Rankine cycle where saturated vapor at 200◦C enters the turbine and saturated liquid at 20◦C exits the condenser. The only properties known for this compound
One kilogram per second water enters a solar collector at 40◦C and exits at 190◦C, as shown in Fig. P12.143. The hot water is sprayed into a direct-contact heat exchanger (no mixing of the two
Find the saturation pressure for refrigerant R-410a at −100 F, assuming it is higher than the triple-point temperature.
Determine the volume expansivity, αp, and the isothermal compressibility, βT , for water at 50 F, 500 lbf/in.2 and at 400 F, 1500 lbf/in.2 using the steam tables.
A cylinder fitted with a piston contains liquid methanol at 70 F, 15 lbf/in.2 and volume 1 ft3. The piston is moved, compressing the methanol to 3000 lbf/in.2 at constant temperature. Calculate the
Liquid methanol at 77 F has an adiabatic compressibility of 7.1 × 1026 in.2/lbf. What is the speed of sound? If it is compressed from 15 psia to 1500 psia in an insulated piston/cylinder, what is
Calculate the difference in internal energy of the ideal gas value and the real gas value for carbon dioxide at the state 70 F, 150 lbf/in.2, as determined using the virial EOS. At this state B =
How low should the pressure be so that nitrous oxide (N2O) gas at 501.6 R can be treated as an ideal gas with 5% accuracy or better?
Nitrous oxide (N2O) at 501.6 R is at a pressure that so it can be in a two-phase state. Find the generalized enthalpy departure for the two saturated states of liquid and vapor.
The new refrigerant R-152a is used in a refrigerator with an evaporator temperature of −10 F and a condensing temperature of 90 F. What are the high and low pressures in this cycle?
Find the heat of evaporation hfg for isobutane (Tc = 735.8 R, Pc = 529.4 psia, M = 58.124) at 54.7 F from the generalized charts and compare to the values in the CATT3 computerized tables.
Carbon dioxide collected from a fermentation process at 40 F, 15 lbf/in.2, should be brought to 438 R, 590 lbf/in.2, in a steady-flow process. Find the minimum work required and the heat transfer
A4-lbm mixture of50%argon and50%nitrogen by mole is in a tank at 300 psia, 320 R. How large is the volume using a model of (a) Ideal gas and (b) Kay’s rule with generalized
A new compound is used in an ideal Rankine cycle where saturated vapor at 400 F enters the turbine and saturated liquid at 70 F exits the condenser. The only properties known for this compound are a
Write a program to obtain a plot of pressure versus specific volume at various temperatures (all on a generalized reduced basis) as predicted by the van der Waals EOS. Temperatures less than the
We wish to determine the isothermal compressibility, βT , for a range of states of liquid water. Use the menu-driven software or write a program to determine this at a pressure of 1 MPa and at 25
Supercritical fluid chromatography is an experimental technique for analyzing compositions of mixtures. It utilizes a carrier fluid, often carbon dioxide, in the dense fluid region just above the
It is desired to design a portable breathing system for an average-sized adult. The breather will store liquid oxygen sufficient for a 24-hour supply and will include a heater for delivering oxygen
Liquid nitrogen is used in cryogenic experiments and applications where a nonoxidizing gas is desired. Size a tank to hold 500 kg to be placed next to a building and estimate the size of an
The speed of sound is used in many applications. Make a list of the speed of sound at P0, T0 for gases, liquids, and solids. Find at least three different substances for each phase. List a number of
Propane is used as a fuel distributed to the end consumer in a steel bottle. Make a list of design specifications for these bottles and give characteristic sizes and the amount of propane they can
Is mass conserved in combustion? Is the number of moles constant?
Does all combustion take place with air?
How does the dewpoint change as the equivalence ratio goes from 0.9 to 1 to 1.1?
If the nitrogen content of air can be lowered, will the adiabatic flame temperature increase or decrease?
Does the enthalpy of combustion depend on the air–fuel ratio?
Why do some fuels not have entries for liquid fuel in Table 13.3?
Is a heating value a fixed number for a fuel?
Is an adiabatic flame temperature a fixed number for a fuel?
A welder uses a bottle with acetylene and a bottle with oxygen. Why should he use the oxygen bottle instead of air?
Some gas welding is done using bottles of fuel, oxygen, and argon. Why do you think argon is used?
Is combustion a reversible process?
Is combustion with more than 100% theoretical air more or less reversible?
In a picnic grill, gaseous propane is fed to a burner together with stoichiometric air. Find the air–fuel ratio on a mass basis and the total reactant mass for 1 kg of propane burned.
A mixture of fuels is E85, which is 85% ethanol and 15% gasoline (assume octane) by mass. Find the A/F ratio on a mass basis for stoichiometric combustion.
A Pennsylvania coal contains 74.2% C, 5.1% H, 6.7% O (dry basis, mass percent) plus ash and small percentages of N and S. This coal is fed into a gasifier along with oxygen and steam, as shown in
Liquid propane is burned with dry air. A volumetric analysis of the products of combustion yields the following volume percent composition on a dry basis: 8.6% CO2, 0.6% CO, 7.2% O2, and 83.6% N2.
The coal gasifier in an integrated gasification combined cycle (IGCC) power plant produces a gas mixture with the composition:This gas is cooled to 40◦C, 3MPa, and theH2S and NH3 are removed in
The hot exhaust gas from an internal-combustion engine is analyzed and found to have the following percent composition on a volumetric basis at the engine exhaust manifold: 10% CO2, 2% CO, 13% H2O,
Acetylene gas, C2H2, is burned with stoichiometric air in a torch. The reactants are supplied at the reference conditions P0, T0. The products come out from the flame at 2500 K after some heat loss
Hydrogen is burned with stoichiometric air in a steady-flow process in which the reactants are supplied at 100 kPa, 298 K. The products are cooled to 800 K in a heat exchanger. Find the heat transfer
Natural gas (methane) is burned with stoichiometric air, reactants supplied at the reference conditions P0, T0 in a steady-flow burner. The products come out at 800 K. If the burner should deliver 10
Liquid methanol is burned with stoichiometric air, both supplied at P0, T0 in a constant-pressure process, and the products exit a heat exchanger at 900 K. Find the heat transfer per kmol fuel.
A rigid container has a 1:1 mole ratio of propane and butane gas together with a stoichiometric ratio of air at P0, T0. The charge burns, and there is heat transfer to a final temperature of 1000 K.
In a gas turbine, natural gas (methane) and stoichiometric air flow into the combustion chamber at 1000 kPa, 500 K. Secondary air (see Fig. P13.51), also at 1000 kPa, 500 K, is added right after the
Find the enthalpy of combustion and the heating value for pure carbon.
Acetylene gas, C2H2, is burned with stoichiometric air in a torch. The reactants are supplied at the reference conditions P0, T0. The products come out from the flame at 2800 K after a heat loss by
Some type of wood can be characterized as C1H1.5O0.7 with a lower heating value of 19 500 kJ/kg. Find its formation enthalpy.
Agriculturally derived butanol, C4H10O, with a molecular mass of 74.12, also called biobutanol, has a lower heating value LHV =33 075 kJ/kg for liquid fuel. Find its formation enthalpy.
In a picnic grill, gaseous propane and stoichiometric air are mixed and fed to a burner, both at P0, T0. After combustion, the products cool down and exit at 500 K. How much heat transfer was given
E85 is a liquid mixture of 85% ethanol and 15% gasoline (assume octane) by mass. Find the lower heating value for this blend.
Gaseous propane and stoichiometric air are mixed and fed to a burner, both at P0, T0. After combustion, the products eventually cool down to T0.How much heat was transferred for 1 kg propane?
In an experiment, a 1:1 mole ratio propane and butane is burned in a steady flow with stoichiometric air. Both fuels and air are supplied as gases at 298 K and 100 kPa. The products are cooled to
Natural gas, we assume methane, is burned with 200% theoretical air, shown in Fig. P13.75, and the reactants are supplied as gases at the reference temperature and pressure. The products are flowing
Gasoline, C7H17, is burned in a steady-state burner with stoichiometric air at P0, T0, shown in Fig. P13.77. The gasoline is flowing as a liquid at T0 to a carburetor, where it is mixed with air to
An isobaric combustion process receives gaseous benzene, C6H6, and air in a stoichiometric ratio at P0, T0. To limit the product temperature to 2000 K, liquid water is sprayed in after the
A liquid fuel similar to diesel, n-dodecaneC12H26, is sent into a carburetor, where it is vaporized and mixed with air in a stoichiometric ratio. The liquid fuel and air are supplied at T0 and 100
A mixture of fuels is E85, which is 85% ethanol and 15% gasoline (assume octane) by mass. Assume we put the fuel and air, both at T0, P0, into a carburetor and vaporize the fuel as we mix it with
Hydrogen gas is burned with pure O2 in a steady flow burner, shown in Fig. P13.82, where both reactants are supplied in a stoichiometric ratio at the reference pressure and temperature. What is the

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