Thermodynamics True/False (Chapters 1, 2, 3, 4, 5, 6)

A process that violates the second law of thermodynamics violates the first law of thermodynamics.

False

Every process consistent with the conservation of energy and conservation of mass principles can actually occur in nature.

False

For a specified inlet state, exit pressure, and mass flow rate, the power input to a compressor operating adiabatically and at steady state is less than what would be required if the compression occurred isentropically.

False

Hydropower is a nonrenewable means for producing electricity.

False

If a closed system consisting of a simple compressible substance is at equilibrium, only one phase can be present.

False

If superheated water vapor at 30 MPa is cooled at constant pressure, it will eventually became saturated vapor, and with sufficient cooling, condensation to saturated liquid will occur.

False

Kilogram, second, foot, and newton are all examples of SI units.

False

Systems can be studied only from a macroscopic point of view.

False

The pound force, lbf, is equal to the pound mass, lb.

False

The thermodynamic performance of a device such as a turbine through which a mass flows is best analyzed by studying the flowing mass alone.

False

The Kelvin scale is the only absolute temperature scale.

False (Both Kelvin and Rankine are absolute temperature scales.)

Entropy is produced in every internally reversible process of a closed system.

False (By definition, there is no entropy production in an internally reversible process.)

Mass, energy, entropy, and temperature are examples of extensive properties.

False (Entropy and temperature are examples of extensive properties.)

At liquid states, the following approximation is reasonable for many engineering applications: s(T,p) ≈ s(T)g

False (For liquid states, entropy can be estimated by using the saturated liquid value at the given temperature s(T,p) ≈ s(T)f.)

The energy of an isolated system must remain constant, but the entropy can only decrease.

False (Since entropy is produced in all actual processes, the only processes that can occur are those for which the entropy of the isolated system increases; this is known as the increase of entropy principle.)

For a gas modeled as an ideal gas, cv = cp + R, where R is the gas constant for the gas.

False (The actual relationships are cp - cv = R and cp = cv + R)

The entropy change between two states of air modeled as an ideal gas can be directly read from Tables A-22 and A-22E only when the pressure at the two states is the same.

False (The entropy change between two states of air modeled as an ideal gas can be directly read from Tables A-22 and A-22E when the process experiences variable specific heats.)

The entropy of a fixed amount of an ideal gas increases in every isothermal process.

False (The entropy change in an isothermal process: Δs = -R ln(p2 / p1) = R ln(v2 / v1) implies that entropy can either increase (expansion) or decrease (compression).)

A process of a closed system that violates the second law of thermodynamics necessarily violates the first law of thermodynamics.

False (The given system interacts with one reservoir and gives work output, which violates the Second Law. First Law states: Q*h = W.)

The second Carnot corollary states that all power cycles operating between the same two thermal reservoirs have the same thermal efficiency.

False (The second Carnot corollary states that all REVERSIBILE power cycles operating between the same thermal reservoirs have the same thermal efficiency.)

The steady-state form of the control volume entropy balance requires that the total rate at which entropy is transferred out of the control volume be less than the total rate at which entropy enters.

False (The steady-state form of the control volume entropy balance requires that the rate at which entropy is transferred out must exceed the rate at which entropy enters)

One corollary of the second law of thermodynamics states that the change in entropy of a closed system must be greater than or equal to zero.

False (This would only be true for isolated systems.)

The value of the temperature expressed using the Celsius temperature scale is always higher than its value expressed using the Kelvin scale.

False (A value expressed using the Kelvin scale is always 273.15 degrees higher than its value expressed using the Celsius scale)

An open feedwater heater is a special type of counterflow heat exchanger.

False (A feedwater is a direct contact heat exchanger.)

The Clausius statement of the second law denies the possibility of transferring energy by heat from a cooler to a hotter body.

False (According to the Clausius statement, this process is possible if WORK is applied to the system.)

Where mass crosses the boundary of a control volume, the accompanying energy transfer is accounted for by the internal energy of the mass only.

False (Energy transfer includes the effects of kinetic and potential energy as well.)

For a control volume at steady state, mass can accumulate inside the control volume.

False (Flow rate in equals flow rate out at steady state.)

For gases modeled as ideal gases, the ratio of cv/cp must be greater than one.

False (It will always be less than one.)

A two-phase liquid-vapor mixture with equal volumes of saturated liquid and saturated vapor has a quality of 0.5.

False (Quality is determined by mass. X = (mg)/(mf + mg). This relationship shows that the quality will be less than 0.5 due to the fact that mg < mf.)

As velocity decreases in a diffuser, pressure decreases.

False (Remember, velocity and pressure have an inverse relationship. As one goes up, the other goes down. In the case of a diffuser, the velocity decreases. Therefore, the pressure increases.)

Temperature is an extensive property.

False (Temperature does not depend on the size of the system and therefore is intensive.)

According to Archimedes' principle, the magnitude of the buoyant force acting on a submerged body is equal to the weight of the body

False (The buoyant force has a magnitude equal to the weight of the displaced liquid)

A diffuser is a flow passage of varying cross-sectional area in which the velocity of a gas or liquid increases in the direction of the flow.

False (The pressure increases through a diffuser, but the velocity decreases.)

If a system's temperature increases, it must have experienced heat transfer.

False (The temperature of a system may increase due to work transfer, as well)

A significant increase in pressure can be achieved by introducing a restriction into a line through which a gas or liquid flows.

False (This is called a throttling process. Is causes the pressure to decrease and the velocity of the flow to increase)

The specific internal energy of ammonia at 0.45 MPa and 50 *C is 1564.32 kJ/kg.

False (You have to use look up tables and use interpolation... But the specific internal energy at this pressure would actually be 1412.085 kJ/kg.)

A process that is adiabatic cannot involve work

False (adiabatic processes involve work interactions but no heat interactions between the system and its surroundings)

For closed systems undergoing processes involving internal irreversibilities, both entropy change and entropy production are positive in value.

False (Change in entropy can be negative or zero in value.)

Mass is an intensive property.

False (Mass depends on the size of the system and therefore is extensive.)

Air can always be regarded as a pure substance.

False (Not sure?)

A control volume is a special type of closed system that does not interact in any way with its surroundings.

False (This actually describes an isolated system.)

The energy of an isolated system can only increase

False (Not sure? there is not energy transfer in an isolated system, therefore no increase in energy could occur)

If a closed system undergoes a thermodynamic cycle, there can be no net work or heat transfer

False (There can be heat transfer. However, there cannot be mass transfer in a closed system.)

The total energy of a closed system can change as a result of energy transfer across the system boundary by heat and work and energy transfer accompanying mass flow across the boundary.

False (a closed system always contains the same mass; only energy can be transferred across the boundary)

The maximum thermal efficiency of any power cycle operating between hot and cold thermal reservoirs at 1000°C and 500°C, respectively, is 50%.

False. (η = 1 - Tc(K) / Th(K) = 40% (convert T to Kelvin))

A closed system always contains the same matter; there is no transfer of matter across its boundary

True

A gas can be modeled as an ideal gas with constant specific heats when Z = 1.

True

A key step in thermodynamic analysis is the careful listing of modeling assumptions.

True

A mixing chamber is a direct-contact heat exchanger.

True

A polytropic process with n = k is adiabatic.

True

A spring is compressed adiabatically and its internal energy increases

True

A two-phase liquid-vapor mixture has 0.2 kg of saturated water vapor and 0.6 kg of saturated liquid. The quality of 0.25 (25%).

True

As pressure increases toward the critical pressure, the values of vf and vg approach each other.

True

At steady state, conservation of energy asserts the total rate at which energy is transferred into the control volume equal the total rate of energy out.

True

At steady state, conservation of mass asserts the total rate at which mass enters the control volume equals the total rate at which mass exits.

True

At steady state, identical electric fans discharging air at the same temperature in New York City and Denver will deliver the same volumetric flow rate of air.

True

Atmospheric air is normally modeled as an ideal gas.

True

Body organs, such as the human heart, whose shapes change as they perform their normal functions can be studied as control volumes.

True

Both the Kelvin scale and the Rankine scale are absolute temperature scales.

True

Common heat exchanger types include direct-contact, counterflow, parallel-flow, and cross flow heat exchangers.

True

Compressor types include reciprocating, axial flow, centrifugal, and Roots type.

True

Devices that measure pressure include barometers, Bourdon tube gages, and manometers.

True

For a one-inlet, on-exit control volume at steady state, the mass flow rates at the inlet and exit are equal but the inlet and exit volumetric flow rates may not be equal.

True

For a specified inlet state, exit pressure, and mass flow rate, the power developed by a turbine operating at steady state is less than if expansion occurred isentropically.

True

For a system at steady state, no property values change with time.

True

For every control volume at steady state, the total of the entering rates of mass flow equals the total of the exiting rates of mass flow.

True

For heat pumps, the coefficient of performance is always greater than or equal to one

True

For liquid water, the approximation v(T, ρ) ≈ vt(T) is reasonable for many engineering applications.

True

For one dimensional flow, mas flow rate is the product of density, area, and velocity.

True

For reversible refrigeration and heat pump cycles operating between the same hot and cold reservoirs, the relation between their coefficients of performance is gamma_max = βmax + 1.

True

For simple compressible systems, any two intensive thermodynamic properties fix the state.

True

Gage pressure indicates the difference between the absolute pressure of a system and the absolute pressure of the atmosphere existing outside the measuring device.

True

Heat transfer for internally reversible processes of closed systems can be represented as areas on T-s diagrams.

True

If a closed system undergoes a process for which the change in total energy is positive, the heat transfer must be positive

True

If a closed system undergoes a process for which the work is negative and the heat transfer is positive, the total energy of the system must increase

True

If a system is isolated from its surroundings and no changes occur in its observable properties, the system was in equilibrium at the moment it was isolated.

True

If the value of any property of a system changes with time, that system cannot be at steady state.

True

In local surroundings at standard atmospheric pressure, a gage will indicate a pressure of 0.2 atm for a refrigerant whose absolute pressure is 1.2 atm.

True

Intensive properties may be functions of both position and time, whereas extensive properties can vary only with time

True

Pressure is an intensive property.

True

Specific volume, the volume per unit of mass, is an intensive property whereas volume and mass are extensive properties.

True

System integration is the practice of combining components to achieve an overall objective.

True

Temperature is the property that is the same for each of two systems when they are in thermal equilibrium

True

The Carnot efficiency also limits the efficiency of wind turbines in generating electricity.

True

The Kelvin-Planck and Clausius statements of the second law of thermodynamics are equivalent because a violation of one statement implies the violation of the other.

True

The Rankine degree is a smaller temperature unit than the Kelvin degree.

True

The composition of a closed system cannot change

True

The following assumptions apply for a substance modeled as an incompressible substance: The specific volume (and density) is constant and the specific internal energy is a function of temperature only.

True

The human body is an example of an integrated system.

True

The kilogram for mass and the meter for length are examples of SI base units defined relative to fabricated objects.

True

The only entropy transfers to or from control volumes are those accompanying heat transfer.

True

The pressure unit psia indicates an absolute pressure expressed in pounds force per square inch

True

The pressures listed in thermodynamic tables are absolute pressures, not gage pressures.

True

The properties of velocity and elevation are not included in the specification of an intensive thermodynamic state.

True

The specific internal energy and enthalpy of an ideal gas are each functions of temperature alone, but its specific entropy depends on two independent intensive properties.

True

The specific volume is the reciprocal of the density.

True

The value of a temperature expressed using the Rankine scale is always higher than its value expressed using the Fahrenheit temperature scale.

True

The volume of a closed system can change

True

Thermal radiation can occur in a vacuum.

True

Transient operation denotes a change in a state with time.

True

Volume is an extensive property.

True

Volumetric flow rate is expressed in units of m^3/s or ft^3/s.

True

When a closed system undergoes a process between two specified states, the change in temperature between the end states is independent of details of the process.

True

When a system undergoes a Carnot cycle, no entropy is produced within the system.

True

When an ideal gas undergoes a polytropic process with n = 1, the gas temperature remains constant.

True

Work is not a property.

True

When σcycle = 0 in Eq. 5.13, the corresponding cycle is one that you will never encounter on the job.

True (A Clausius inequality of σcycle = 0 implies a reversible system, and a reversible system will never happen in the real world.)

When an isolated system undergoes a process, the values of its energy and entropy can only increase or remain the same.

True (Energy cannot increase or decrease, and entropy can only increase or remain the same.)

The change in entropy of a closed system is the same for every process between two specified end states.

True (Entropy is a state function, meaning that the entropy of a specified state depends only on a state of that system.)

One statement of the second law of thermodynamics recognizes that the extensive property entropy is produced within systems whenever internal irreversibilities are present.

True (Entropy is produced within the system due to irreversibility's, which are caused by friction and other nonidealities.)

Friction associated with flow of fluids through pipes and around objects is one type of irreversibility.

True (Friction is one of eight types of irreversibilities.)

In statistical thermodynamics, entropy is associated with the notion of microscopic disorder.

True (In a spontaneous process of an isolated system, the system moves toward equilibrium and the entropy increases. From the microscopic viewpoint, this is equivalent to saying that as an isolated system moves toward equilibrium our knowledge of the condition of individual particles making up the system decreases, which corresponds to an increase in microscopic disorder and a related increase in entropy.)

There are no irreversibilities within a system undergoing an internally reversible process.

True (In general, internally reversible refers to a system which can be reverted back to its original state.)

When left alone, systems tend to undergo spontaneous changes until equilibrium is attained, both internally and with their surroundings.

True (In some cases, equilibrium is reached quickly, in others it's achieves slowly.)

The Carnot cycle is represented on a T-s diagram as a rectangle.

True (Note: A Carnot cycle is defined as two adiabatic processes and two isothermal processes.)

A closed system can experience a decrease in entropy only when there is heat transfer from the system to its surroundings during the process.

True (Since entropy transfer accompanies the heat transfer, system entropy decreases.)

The T dS equations are fundamentally important in thermodynamics because of their use in deriving important property relations for pure, simple compressible systems.

True (The T dS equations allow entropy changes to be evaluated from other more readily determined property data. NOTE: In addition, they are used as a point of departure for deriving many important property relations for pure, simple com- pressible systems, including means for constructing the property tables giving u, h, and s.)

The entropy of a fixed amount of an incompressible substance increases in every process for which temperature increases.

True (The entropy change for an incompressible substance, s2 - s1 = c ln(T2 / T1), implies that Δs and ΔT are directly proportional.)

When a net amount of work is done on a closed system undergoing an internally reversible process, a net heat transfer of energy from the system also occurs.

True (The net work of any cycle is equal to the net heat transfer.)

In an adiabatic and internally reversible process of a closed system the entropy remains constant.

True (This process is called isentropic (constant entropy).)

The entropy change of a closed system during a process can be greater than, equal to, or less than zero.

True (When a closed system undergoing an internally reversible process receives energy by heat transfer, the system experiences an increase in entropy. Conversely, when energy is removed from the system by heat transfer, the entropy of the system decreases. In an adiabatic internally reversible process, entropy remains constant.)

The maximum coefficient of performance of any refrigeration cycle operating between cold and hot reservoirs at 40°F and 80°F, respectively, is closely 12.5.

True (β = Tc / (Th - Tc) = 12.49.)

Carbon dioxide (CO2) at 320 K and 55 bar can be modeled as an ideal gas.

True (320 K is above the critical temperature and 55 bar is below the critical pressure.)

When a substance undergoes a throttling process through a valve, the specific enthalpies of the substance at the valve inlet and exit are equal.

True (The equation for a throttling process is h1 = h2)

For any cycle, the net amounts of energy transfer by heat and work are equal.

True (In a cycle, Qcyc = Wcyc)

In principle, expansion or compression work can be evaluated using ∫ p dV for both actual and quasi-equilibrium expansion processes.

True.

Only changes in the internal energy of a system between two states have significance; no significance can be attached to the internal energy at a state.

True.

The change in entropy of a closed system is the same for every process between two specified states.

True. (Since entropy is a property, the change in entropy of a system in going from one state to another is the same for all processes, both internally reversible and irreversible, between these two states.)

In principle, the Clausius inequality applies to any cycle.

True. (∮(δQ / T)b = -σ is for any cycle.)

Internally reversible processes do not actually occur but serve as hypothetical limiting cases as internal irreversibilities are reduced further and further.

True. (All actual processes are irreversible, but a reversible process may be used to approximate a process.)

The increase of entropy principle states that the only processes of an isolated system that are possible are those for which the entropy increases.

True. (Since entropy is produced in all actual processes, the only processes that can occur are those for which the entropy of the isolated system increases.)