thermo final
Which of the following results in the highest heat transfer from a rigid combustor? "Complete" combustion products at dew point temperature "Complete" combustion products below dew point temperature "Complete" combustion products at adiabatic flame temperature "Complete" combustion products above adiabatic flame temperature
"Complete" combustion products below dew point temperature
If the air temperature of dead state is 20oC and pressure is 1 atm, which of the following states has the lowest exergy? (a) A state at 20oC and 1 atm (b) A state at 0oC and 1 atm (c) A state at 0 K and 1 atm
(a) A state at 20oC and 1 atm
What happens to entropy of air during an isothermal expansion process? (a) Increases (b) Decreases (c) Remains the same
(a) Increases
A cold storage warehouse refrigerates meat in a compartment to -40oC, a deep freezer chills fish in a compartment to -22oC and a wine cooler chills wine in a compartment to 8oC. If they consume the same amount of electricity, operate under the same environmental temperature at 25oC, and have same heat transfer, which has highest exergetic (2nd law) efficiency? (a) The cold storage warehouse (b) The deep freezer (c) The wine cooler
(a) The cold storage warehouse
If humid air at 30oC and 85% relative humidity is cooled and dehumidified by a cooling coil, the relative humidity of the air will (a) increase (b) decrease (c) remain the same
(a) increase
Two air steams with different temperature but the same relative humidity are mixed adiabatically in an air conditioning system. The relative humidity of the mixture will (a) increase (b) decrease (c) remain the same
(a) increase
Backwork ratio for the Brayton cycle is ___________ that for the Rankine cycle.
(a) much larger than
Which of the following approximations is used in the Clausius-Clapeyron equation? (a) vg = RT/p (b) pressure change cannot be too large (c) temperature change cannot be too large (d) all of the above
(a) vg = RT/p
Which of the following is a product of complete stoichiometric combustion of a hydrocarbon fuel? (a) CO (b) H2O (c) C (d) O2
(b) H2O
For an open system, ___________ process of air compression requires least work input.
(b) Isothermal
A rigid tank that contains a mixture of two ideal gases is chilled to a lower temperature and pressure. Assuming there are no reactions, the partial pressure of each component will (a) increase (b) decrease (c) remain the same
(b) decrease
If propane in a rigid container leaks out of the container at constant rate, then the propane within the container is at (a) steady state (b) transient state (c) a state that cannot be determined
(b) transient state
] One kmol/s of gaseous CH4 and 150% theoretical air flow into a steady state combustor. The product contains ___________.
(c) CO2, H2O, O2, N2
System (1) undergoes a reversible process and System (2) an irreversible process from the same initial state to the same final state. Which of the following is correct? (a) System (1) has a higher final specific exergy than System (2) (b) System (2) has a higher final specific exergy than System (1) (c) System (1) has the same final specific exergy as System (2)
(c) System (1) has the same final specific exergy as System (2)
Two kmol of H2 is burned in a closed system. Which case would lead to the highest adiabatic flame temperature? (a) combustion with 100% theoretical air (b) combustion with 100% excess air (c) combustion with one kmol of O2
(c) combustion with one kmol of O2
For a vapor-compression heat pump cycle, the coefficient of performance is the magnitude of the heat transfer to or from the ___________ divided by the pump work.
(c) condenser
Which of the following results in the highest adiabatic flame temperature when a fuel is burned? (2 points) 100% Theoretical Air 200% Theoretical Air 100% Theoretical Oxygen 50% Theoretical Air
100% Theoretical Oxygen
Gaseous methane is burned with excess air to produce an equilibrium mixture of H2O(g), CO2, CO, O2, N2, and NO. How many equilibrium constant equations are needed to calculate the equilibrium composition? (2 points)
2
Methane burns completely with dry air in a constant-pressure combustor. Which of the following has a lower dew point temperature for combustion products?
200% theoretical air
The Purdue power plant uses heat produced from combustion of natural gas to generate 20 MW of electrical power each day with a generation efficiency of 30%. (i) Find the energy released by the combustion process:
66.67 MW
Consider a given fuel burning with 100% dry air. Which of the following is correct?
Adiabatic flame temperature is higher than equilibrium flame temperature
Q6: Which of the following cause incomplete combustion? (a) Insufficient time for combustion to occur (b) Insufficient oxygen in the reactants (c) Insufficient mixing of reactants (d) All of above
All of above
Which is more likely to be found in the products of incomplete combustion of a hydrocarbon fuel, CO or OH? CO OH Insufficient Information
CO
A rigid tank that contains a mixture of two ideal gases is cooled to a lower temperature. Assuming there are no reactions, will the partial pressure of each gas component Increase Decrease Remain the same
Decrease
A saturated liquid-vapor mixture of water has a temperature of 150°C . Given no further information about the state of the mixture, which of the following thermodynamic properties can be determined?Enthalpy Specific enthalpy Pressure Specific volume
Enthalpy
Enthalpy of formation is always positive. (2 points) True False Insufficient Information
False
deltaG for a chemical reaction is always positive. (2 points) True False Insufficient Information
False
For which of the following processes is entropy always generated? Frictionless work addition Heat transfer across a finite temperature gradient Isothermal heat transfer
Heat transfer across a finite temperature gradient
Suppose a window style air conditioner is wheeled on a table into a sealed and well-insulated room, plugged in, and turned on. The air temperature of the room will: Increase Decrease Remain the same
Increase
When the air in a poorly-insulated piston-cylinder device is compressed, what happens to the air exergy? Always increase Always decrease Insufficient information
Insufficient information
A system undergoes a process from an initial state 1 to a final state 2. For the given change in entropy 2 1 S S − , for which process will the entropy generation σ12 be the greatest? Adiabatic process Isothermal heat rejection process Isothermal heat addition process
Isothermal heat rejection process
Is the statement correct: "Exergy is destroyed whenever there is a change in entropy"?
No
Is this statement correct: "If the entropy change of a process is zero, the process must be reversible"? Yes No Insufficient information
No
Is this statement correct: "The specific internal energy of an ideal gas mixture is equal to the sum of the specific internal energy of each individual gas in the mixture."? Yes No Insufficient information
No
Is this statement correct?: "According to Dalton's model, the total volume of a mixture of ideal gases is equal to the sum of partial volumes of individual gases in the mixture". Yes No
No
Is this statement correct?: "Enthalpy of formation is always negative". Yes No Insufficient information
No
Is this statement correct?: "Exergy transfer with work in a given process is always lower than the work in the process". Yes No
No
Is this statement correct?: "Heat transfer in a given process and exergy transfer associated with the heat transfer in the process always have the same sign". Yes No
No
Is this statement correct?: "If the entropy change of a system (without surroundings) during a process is negative, then the process is impossible". Yes No
No
Is this statement correct?: "In the van der Waals equation of state, the constant b accounts for intermolecular forces". Yes No Insufficient information
No
Is this statement correct?: "The exergy of a closed system A (TA > T0, PA = P0) is always higher than that of another closed system B (TB < T0, PB = P0)". Assume kinetic and potential energy effects are negligibly small for both the systems. Yes No
No
Which of the following condition will have enthalpy and entropy departure values close to 0? P <<< Pcritical, T <<< Tcritical P <<< Pcritical, T >>> Tcritical P >>> Pcritical, T >>> Tcritical P >>> Pcritical, T <<< Tcritical
P <<< Pcritical, T >>> Tcritical
What happens to specific volume of an ideal gas when the pressure is doubled and the absolute temperature is halved?
Quartered
) Which of the following is true for superheated vapor? T = Tsat, P = Psat T > Tsat, P < Psat T > Tsat, P > Psat
T > Tsat, P < Psat
Which of the following expressions is correct for moist air? Twet,bulb >Tdry,bulb >Tdewpoint Tdry,bulb >Twet,bulb >Tdewpoint Tdry,bulb >Tdewpoint> Twet,bulb
Tdry,bulb >Twet,bulb >Tdewpoint
Equilibrium flame temperature is always less than adiabatic flame temperature. (2 points) True False Insufficient Information
True
Gibbs free energy of a product mixture attains a minimum value at the condition of chemical equilibrium. (2 points) True False Insufficient Information
True
Which of the following mixing processes does not generate entropy? Two chemically different gases at the same initial pressure and temperature Two chemically identical gases at the same initial pressure and temperature Two chemically identical gases at the same initial temperature but at different initial pressures
Two chemically identical gases at the same initial pressure and temperature
(ii) (a) Which of the following is (are) correct? Circle all that apply. Dry bulb temperature is always higher than wet bulb temperature. Wet bulb temperature is approximately equal to adiabatic saturation temperature. Relative humidity is always less than 100%. Liquid water condenses below dew point temperature.
Wet bulb temperature is approximately equal to adiabatic saturation temperature. Liquid water condenses below dew point temperature.
(8) Which of the following is always true for moist air at atmospheric pressure? Wet bulb temperature is nearly equal to dry bulb temperature Wet bulb temperature is nearly equal to adiabatic saturation temperature Wet bulb temperature is nearly equal to dew point temperature
Wet bulb temperature is nearly equal to adiabatic saturation temperature
One kmol of H2 is burned in a closed system. Which case has the highest adiabatic flame temperature? With 100% theoretical air With 100% excess air With 0.5 kmols of pure O2
With 0.5 kmols of pure O2
For an ideal gas, are temperature and volume independent properties?
Yes
Is the exergy of a system different in different surrounding environments? Yes No Insufficient information
Yes
Is this statement correct: "Only irreversible effects destroy exergy during thermodynamic processes"? Yes No Insufficient information to judge
Yes
An ideal gas goes from State 1 to State 2 as it flows across a throttle. Which of the following statements is true? a. h2=h1 b. u2 = u1 c. s2 = s1 d. T2 < T1
a. h2=h1
The Maxwell relations are valid for . Which phrase correctly completes the previous sentence? only two-phase mixture only ideal gas all phases
all phases
The additional constants (a and b) in the van der Waals equation of state account for which of the following? (a) the volume of the individual molecules (b) the intermolecular forces (c) both the volume of the individual molecules and the intermolecular forces
both the volume of the individual molecules and the intermolecular forces
Moist air with a relative humidity ϕ=1 is compressed isothermally from State 1 to State 2. Which of the statements below is correct? a) ω2 = ω1 b) ϕ2 > ϕ1 c) ϕ2 < ϕ1 d) ω2 < ω1
d) ω2 < ω1
Consider the equilibrium reaction: H2O <> H2 + 0.5O2. What happens to the number of moles of H2 if pressure increases at constant temperature?
decrease
Methane (CH4) burns completely with x% of theoretical air. The products are subsequently cooled at a pressure of 1 bar. As x increases from 100 to 150, the corresponding dew point temperature increases decreases remains the same
decreases The mole fraction of H2O decreases as the percent of theoretical air increases from 100 to 150. Then, the partial pressure of H2O decreases, which means the dew point temperature decreases.
A closed, rigid tank contains a mixture of N2O and CO2. The mass fraction of N2O is _______ the mole fraction of N2O.
equal
True False.In turbojets, propulsive thrust force is proportional to the product of the inlet and exit air velocities.
false
True False.Lowering the average temperature of heat addition increases efficiency in a Rankine cycle.
false
True False.The Clausius-Clapeyron equation applies to phase change between any two phases.
false
True False.The maximum theoretical COP of a vapor compression system is infinite.
false
A well-insulated vessel contains two compartments with ideal gases at the same temperature and pressure in each compartment. One compartment contains O2 and the other contains CO2. When the partition dividing the two compartments is removed, the entropy of the system will increase decrease remain constant
increase
A closed, rigid tank containing a mixture of 21% O2 and 79% N2 (by mole fractions) is heated to a higher pressure and temperature. What happens to the partial pressure of O2? Assume there are no reactions.
increases
Consider the stoichiometric reaction CO2 ⇌ CO + 0.5O2. What will happen to the moles of CO2 if the pressure doubles under a constant temperature process? increases decreases remains the same
increases. Since temperature is constant, K is constant. Therefore, an increase in P will be require an increase in the moles of CO2 based on the equation of reaction equilibrium.
The van der Waals equation of state . Which phrase correctly completes the previous sentence? is less accurate than property tables is less accurate than ideal gas equation cannot be used for superheated vapor
is less accurate than property tables
The adiabatic flame temperature for a fuel lean combustion reaction is that for the same fuel with 100% theoretical air. lower than higher than the same as
lower than
Entropy departure is the difference between the entropy of a real substance and (a) the entropy of an ideal gas of the same substance at the same temperature and pressure (b) the entropy of an ideal gas of the same substance at 25oC and 1 atm (c) the entropy of an ideal gas of the same substance at its critical point
the entropy of an ideal gas of the same substance at the same temperature and pressure
True False. The back work ratio for a Rankine cycle is lower than that for a Brayton cycle.
true
True False.In a Brayton refrigeration cycle, the expansion process is achieved using a turbine
true
True False.Intercooling in a Brayton cycle requires a multi-stage compressor.
true
True False.The use of heat pumps is limited in very cold environments because of the need to expand the refrigerant to a colder temperature than the ambient environment.
true
True/False. The throttling process in heat pumps can be modeled as isenthalpic
true
