Chapter 7

Question 1

Clausius equality

Answer 1

The equality in the Clausius inequality holds for totally or just internally reversible cycles and the inequality for the irreversible ones

Question 2

____ is an extensive property of a system

Answer 2

Entropy

Question 3

The entropy change between two specified states…

Answer 3

Is the same whether the process is reversible or irreversible

Question 4

Internally reversible isothermal heat transfer process

Answer 4

This equation is particularly useful for determining the entropy changes of thermal energy reservoirs

Question 5

The net change in volume (a property) during a cycle is always ____

Answer 5

Zero

Question 6

The increase of entropy principle

Answer 6

The equality holds for an internally reversible process and the inequality for an irreversible process

Some entropy is generated or created during an irreversible process, and this generation is due entirely to the presence of irreversibilities

The entropy generation Sgen is always a positive quantity or zero

Question 7

The entropy change of an isolated system…

Answer 7

The sum of the entropy changes of its components, and is never less than zero

Question 8

A system and its surroundings form an ______

Answer 8

Isolated system

Question 9

Sgen > 0

Answer 9

Irreversible process

Question 10

Sgen = 0

Answer 10

Reversible process

Question 11

Sgen < 0

Answer 11

Impossible process

Question 12

The entropy change of a system can be _____

Answer 12

Negative

Question 13

Can entropy generation (Sgen) be negative?

Answer 13

No

Question 14

Entropy

Answer 14

1. Processes can occur in a direction only, not in any direction.
2. Entropy is a nonconserved property and there is no such thing as the conservation of entropy principle
3. The performance of engineering systems is degraded by the presence of irreversibilities and entropy is a measure of the magnitudes of the irreversibilities during that process. It is also used to establish criteria for the performance of engineering devices

Question 15

Processes can occur in a direction only, not in any direction

Answer 15

A process must proceed in the direction that complies with the increase of entropy principle (Sgen >= 0)

A process that violates this principle is impossible

Question 16

Entropy is a non-conserved property

Answer 16

Entropy is conserved during the idealized reversible processes only and increases during all actual processes

Question 17

Entropy change of pure substances

Answer 17

Entropy is a property, and thus the value of entropy of a system is fixed once the state of the system is fixed

Determined from the tables

Question 18

A process during which the entropy remains constant

Answer 18

Isentropic process

Question 19

Isentropic process

Answer 19

During an internally reversible, adiabatic process

Appears as a vertical line segment on a T-s diagram

Question 20

On a T-s diagram, the area under the process curve represents…

Answer 20

The heat transfer for internally reversible processes

Question 21

Mollier diagram

Answer 21

The h-s diagram

Question 22

For adiabatic steady-flow devices, h-s diagrams

Answer 22

The vertical distance (change in h) is a measure of work

The horizontal distance (change in s) is a measure of irreversibilities

Question 23

The level of molecular disorder (entropy) of a substance _______ as it melts or evaporates

Answer 23

Increases

Question 24

A pure crystalline substance at absolute zero temperature is in perfect order and its entropy is zero

Answer 24

The third law of thermodynamics

Question 25

Disorganized energy

Answer 25

Does not create must useful effect, no matter how large it is

Question 26

In the absence of friction, raising a weight by a rotating shaft...

Answer 26

Does not create any disorder (entropy) and energy is not degraded during this process

Question 27

The paddle-wheel work done on a gas...

Answer 27

Increases the level of disorder (entropy) of the gas and energy is degraded during this process

Question 28

During a heat transfer process, the net entropy ____

Answer 28

Increases Hot body - decreases Cold body - increases

Question 29

T ds Relations

Answer 29

Valid for both reversible and irreversible processes and for both closed and open systems

Question 30

Liquids and solids can be approximated as _____ since their specific volumes remain nearly constant during a process

Answer 30

Incompressible substances

Question 31

For solids and liquids, an isentropic process is also ____

Answer 31

Isothermal

Question 32

A reversible turbine delivers more work than an irreversible one if...

Answer 32

Both operate between the same end states

Question 33

The adiabatic compression requires the ____ work

Answer 33

Maximum

Question 34

The isothermal compression requires the ____ work

Answer 34

Minimum

Question 35

The gas is compression in stages and cooled between each stage by passing it through a heat exchanger called an ____

Answer 35

Intercooling

Question 36

To minimize compression work during two-stage compression, the pressure ratio across each stage of the compressor...

Answer 36

Must be the same

Question 37

Isentropic process

Answer 37

Involves no irreversibilities Serves as the ideal process for adiabatic devices

Question 38

Can you use isentropic efficiency for a non-adiabatic compressor?

Answer 38

No

Question 39

Can you use isothermal efficiency for an adiabatic compressor?

Answer 39

Yes

Question 40

Compressors are sometimes intentionally cooled to...

Answer 40

Minimize the work input

Question 41

Mechanisms of Entropy Transfer

Answer 41

1. Heat transfer | 2. Mass flow

Question 42

Entropy transfer by work

Answer 42

0