Thermo - Final

The quality of saturated liquid is ___.

0

The quality of saturated vapor is ___.

1

Select the appropriate definition for a turbine.

A device in which power is developed as a result of a gas or liquid passing through a set of blades attached to a shaft free to rotate.

Select the appropriate definition for a compressor

A device in which work is done on a gas to increase the pressure and/ or elevation.

Select the appropriate definition for a pump.

A device in which work is done on a liquid to increase the pressure and/ or elevation.

Select the appropriate definition for a diffuser.

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

Select the appropriate definition for a nozzle.

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

Uses of the second law of thermodynamics include ___.

All of the answers are correct. Defining the Kelvin scale, predicting the direction of processes, developing means for evaluating internal energy in terms of more readily measured properties

Irreversibilities present in an internal combustion engine include:

All of the answers are correct. Friction, heat transfer, chemical reaction

Which of the following are true statements about a system at the dead state?

All of the answers are correct. It is in thermal equilibrium with the environment, it is in mechanical equilibrium with the environment, the value of the thermomechanical contribution to exergy is zero.

Which irreversibilities are present during the operation of a cell phone?

All of the answers are correct: heat transfer between the cell phone and its surroundings, electric current flow through a resistance, spontaneous chemical reaction in the battery

Which of the following terms is defined as: "The state when a system is at T0 and p0 and at rest relative to the exergy reference environment."

Dead State

Which of the following terms is defined as: "The state when a system is at To and Po and at rest relative to the exergy reference environment."

Dead state

For a closed system, as the exergy reference environment temperature ___, the exergy destruction rate decreases.

Decreases

The time rate of change of the energy contained within a one-inlet, one-exit control volume at time t equals ___.

Equation:

Which expression is used to determine the exergy of the steam within the tank?

Esteam= msteam [(u1-uo) + Po(v1-vo) - To(s1-so)]

Which of the following terms is defined as: "The maximum theoretical work obtainable from an overall system consisting of a system and the environment as the system comes to equilibrium with the environment."

Exergy

A nozzle can be modeled as a throttling process. T/F

False

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

False

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

False

As velocity decreases in a diffuser, pressure decreases. T/F

False

Cooling of computer components achieved by a fan-induced air flow falls within the realm of radiation heat transfer. T/F

False

Exergy can be transferred to, and from, closed systems accompanying heat transfer, work, and mass flow.

False

For a control volume at steady state, mass can accumulate within the control volume. T/F

False

Generally, only one design solution is feasible based on the design constraints related to economics, safety, environmental impact, and so on. T/F

False

In a throttling process, energy and exergy are conserved.

False

Mass, volume, energy, entropy, and exergy are all intensive properties.

False

Since exergy is an extensive property, it is not possible to work with it on a unit mass or molar basis.

False

Temperature is an extensive property. T/F

False

The Kelvin scale is the only absolute temperature scale. T/F

False

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

False

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

False

The specific enthalpy is defined as h = u - pv. T/F

False

When a closed system is at the dead state, it is in thermal and mechanical equilibrium with the exergy reference environment, and the values of the system's energy and thermomechanical exergy are each zero.

False

Which of the following terms is defined as: "The exergy associated with mass entering or exiting a control volume."

Flow exergy

Which of the following statements does not describe the exergy reference environment?

It is incompressible.

The h-s diagram is commonly known as the ___ diagram.

Mollier

A closed system undergoes a process for which S2 = S1. Must the process be internally reversible?

No

The following term reduces to zero within the steady-state form of the closed system exergy rate balance.

The time rate of the change of exergy within the closed system.

Which of the following terms is defined as: "The consideration of costs when it comes to the design and operation of thermal systems."

Thermoeconomics

At every state, exergy cannot be negative; yet exergy change between two states can be positive, negative, or zero.

True

Exergy destruction is proportional to entropy production.

True

Exergy is destroyed by irreversibilities. T/F

True

Exergy transfer accompanying heat transfer is a function of the environment temperature and the temperature of the boundary where heat transfer occurs.

True

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

True

For heat pumps, the coefficient of performance gamma is always greater than or equal to one. T/F

True

For one-dimensional flow, mass flow rate is the product of density, area, and velocity. T/F

True

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

True

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

True

In principle, expansion or compression work can be evaluated us integral pdV for both actual and quasiequilibrium expansion processes. T/F

True

Pressure is an intensive property. T/F

True

Referring to the figure, if the air in the tank were at a pressure below the atmospheric pressure, air would flow spontaneously spontaneously into the tank from the surrounding atmosphere until the pressure in the tank equaled that of the atmosphere. T/F

True

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

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. T/F

True

The specific volume is the reciprocal of the density. T/F

True

The units of exergy are the same as those of energy.

True

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

True

To define exergy, we think of two systems: a system of interest and an exergy reference environment.

True

Volume is an extensive property. T/F

True

Volumetric flow rate is expressed in units of m3/s or ft3/s. T/F

True

According to the increase of entropy principle, is it possible for the entropy of a system to increase?

Yes

Whenever heat transfer occurs for a closed system, there is a corresponding entropy transfer. Are the directions the same?

Yes

In regard to the exergy of a system, when the system is at rest relative to its environment, the values of its kinetic and potential energies are ___.

Zero

If a process is modeled as occurring without heat transfer, the process is said to be an ___ process.

adiabatic

A control volume is a system that ___.

allows a transfer of matter across its boundary.

The terms in the energy balance for a closed system are:

change in energy, amount of energy transfer by heat, amount of energy transfer by work

A subcooled liquid is alternatively referred to as a ___ liquid.

compressed

A gas contained within a piston-cylinder assembly undergoes Process 1-2-3 shown on the pressure-volume diagram in the following figure. Process 1-2-3 is:

constant-pressure expansion followed by a constant-volume process

The mode of energy transfer between a solid at a temperature Tb and an adjacent gas or liquid at another temperature Tf is commonly referred to as ___ heat transfer.

convection

Are the kinetic and gravitational potential energies of a closed system intensive of extensive properties?

extensive

The coefficient of performance of a reversible refrigeration cycle is always ___ the coefficient of performance of an irreversible refrigeration cycle when each operates between the same two thermal reservoirs.

greater than

For a one-inlet, one-exit control volume at steady state, the specific entropy at the exit must be ___ the specific entropy at the inlet if there is no heat transfer.

greater than or equal to

A flow idealized as a throttling process through a device has ___.

h2 = h1 and p2 < p1

For heating a home, does electrical resistance baseboard heating or a heat pump use less electricity?

heat pump

Total energy is the sum of:

internal energy, kinetic energy, and potential energy

A throttling process is ___.

irreversible.

SI base units include ___.

kelvin (K), meter (m), second (s)

Kinetic energy is a function of:

mass and velocity

Potential energy is a function of:

mass, acceleration of gravity, and elevation

According to the sign convention for heat transfer, energy transfer by heat from the system to its surroundings is considered ___.

negative

A closed system undergoes a process in which work is done of the system and heat transfer Q occurs only at a location on the boundary where the temperature is Tb. Determine whether the entropy change of the system is positive, negative, zero, or indeterminate. Internal irreversibilities present, Q > 0.

positive

The line labeled a on the figure is a line of constant ___.

pressure

The list consisting only of intensive properties is ___.

pressure, temperature, specific volume

A substance that is uniform and invariable in chemical composition is called a ___ substance.

pure

A system is said to be at ___ if none of its properties changes with time.

steady state

___ means all properties are unchanging in time.

steady state

Referring to the figure, the thermal efficiency at point b is greater than the thermal efficiency at point a because ___.

the value of Th increases

Which relationship is used to determine the specific internal energy at the dead state?

uo ~ uf(To)

Specific volume on a molar basis, v-, is related to specific volume on a mass, v, basis by ___.

v- = vM