CHAPTER 5

Question 1

Considered to be the most fundamental law of science.

Answer 1

The Second Law of Thermodynamics

Question 2

CP Snow in his Two Cultures wrote:

Answer 2

“Not knowing the Second Law of Thermodynamics is like never having read a work of Shakespeare”.

Question 3

Einstein regarded Thermodynamics

Answer 3

“A law is more impressive the greater the simplicity of its premises, the more different are the kinds of things it relates, and the more extended its range of applicability. (..) It is the only physical theory of universal content, which I am convinced, that within the framework of applicability of its basic concepts will never be overthrown.”

Question 4

In fact in modern times the second law of
thermodynamics is being used to even explain popular theories like

Answer 4

Big bang, expansion of the cosmos and how the time is fast tickling away towards the “heat death” of the universe.

Question 5

1st Aspects of the Second Law

Answer 5

1. Predicting the direction of processes.

Question 6

2nd Aspects of the Second Law

Answer 6

2. Establishing conditions for equilibrium.

Question 7

3rd Aspects of the Second Law

Answer 7

3. Determining the best theoretical performance of cycles, engines, and other devices.

Question 8

4th Aspects of the Second Law

Answer 8

4. Evaluating quantitatively the factors that preclude the attainment of the best theoretical performance level.

Question 9

5th Aspects of the Second Law

Answer 9

5. Defining a temperature scale independent of the properties of any thermometric substance.

Question 10

6th Aspect of the Second Law

Answer 10

6. Developing means for evaluating properties such as u and h in terms of properties that are more readily obtained experimentally.

Additional Uses:

It also has been used in philosophy, economics, and other disciplines far removed from engineering thermodynamics.

Question 11

Three alternative statements of the second law of thermodynamics:

Answer 11

1. Clausius statement
2. Kelvin–Planck statement
3. Entropy statement

Question 12

Clausius Statement of the second law of thermodynamics

Answer 12

“It is impossible for any system to operate in such a way that the sole result would be an energy transfer by heat from a cooler to a hotter body.

Question 13

Kelvin–Planck Statement of the second law of thermodynamics

Answer 13

“It is impossible for any system to operate in a thermodynamic cycle and deliver a net amount of energy by work to its surroundings while receiving energy by heat transfer from a single thermal reservoir.”

Question 14

Entropy Statement of the second law of thermodynamics

Answer 14

“It is impossible for any system to operate in a way that entropy is destroyed.”

Question 15

One of Europe’s elite theoretical physicists, was born in Köslin, Poland, in 1822.

Answer 15

Rudolf Julius Emanuel Clausius

Question 16

German Physicist and Mathematician

Answer 16

Rudolf Julius Emanuel Clausius

Question 17

Contributed to the theory of electrolysis (the breaking down of a compound by electricity)

Answer 17

Rudolf Julius Emanuel Clausius

Question 18

A special kind of system that always remains at constant temperature even though energy is added or removed by heat transfer.

Answer 18

Thermal reservoir/ reservoir

Question 19

Thermodynamic cycle

Answer 19

Sequence of processes that begins
and ends at the same state.

Question 20

Analytical form of the Kelvin–Planck statement:

Answer 20

Wcycle ≤ 0 (Single Reservoir)

Question 21

Lord Kelvin (1824-1907)

Answer 21

Devising the absolute temperature scale, now called the ‘Kelvin scale’

Question 22

Formulating the second law of thermodynamics

Answer 22

Lord Kelvin (1824-1907)

Question 23

Working to install telegraph
cables under the Atlantic.

Answer 23

Lord Kelvin (1824-1907)

Question 24

In 1884 Kelvin travelled to the United States to give a series of lectures. These were enthusiastically received, and were published in 1904 as the ‘Baltimore Lectures’

Answer 24

Lord Kelvin (1824-1907)

Question 25

Max Karl Ernst Ludwig Planck

Answer 25

born in Kiel, Germany, on April 23, 1858

Question 26

Who was able to deduce the relationship between the energy and the frequency of radiation.

Answer 26

Max Karl Ernst Ludwig Planck

Question 27

Who studied at the Universities of Munich and Berlin, where his teachers included Kirchhoff and Helmholtz, and received his doctorate of philosophy at Munich in 1879.

Answer 27

Max Karl Ernst Ludwig Planck

Question 28

Mass and energy are familiar examples of extensive properties of systems. What is another example of extensive property?

Answer 28

Entropy

Question 29

Like mass and energy, what can be transferred across the system boundary?

Answer 29

Entropy

Question 30

There is a single means of entropy transfer—namely, entropy transfer accompanying heat transfer.

Answer 30

Closed System

Question 31

Unlike mass and energy, which are conserved, entropy is ________ within systems whenever nonidealities (called irreversibilities) such as friction are present

Answer 31

Produced

Question 32

Reversible process

Answer 32

A process that can be reversed without leaving any trace on the surroundings. It means both system and surroundings are returned to their initial states at the end of the reverse process. *Do not occur *Idealizations of actual processes. *Things happen very slowly, without any resisting force, without any space limitation *Everything happens in a highly organized way

Question 33

Irreversible process

Answer 33

*One in which heat is transferred through a finite temperature. *Processes that are not reversible are called irreversible.

Question 34

2 Types of Reversible Process

Answer 34

1. Internally 2. Externally Both are Totally Reversible

Question 35

If no irreversibilities occur within the boundaries of the system. *System undergoes through a series of equilibrium states, and when the process is reversed, the system passes through exactly the same equilibrium states while returning to its initial state.

Answer 35

Internally Reversable Process

Question 36

If no irreversibilities occur outside the system boundaries during the process. *Heat transfer between a reservoir and a system is an externally reversible process if the surface of contact between the system and reservoir is at the same temperature.

Answer 36

Externally Reversible Process

Question 37

2 Types of Irreversible Process

Answer 37

1. External irreversibilities 2. Internal irreversibilities

Question 38

These are associated with dissipating effects outside the working fluid. Example: Mechanical friction occurring during a process due to some external source.

Answer 38

External Irreversibilities

Question 39

These are associated with dissipating effects within the working fluid. Example: Unrestricted expansion of gas, viscosity and inertia of the gas

Answer 39

Internal Irreversibilities

Question 40

For two thermal reservoirs, a hot reservoir and a cold reservoir, The thermal efficiency of the cycle is:

Answer 40

n = Wcycle/QH = 1 - Qc/QH

Question 41

For a refrigeration cycle the coefficient of performance (COP) is

Answer 41

B = Qc/Wcycle =Qc/QH-Qc

Question 42

The coefficient of performance (COP) for a heat pump cycle is

Answer 42

y = QH/Wcycle = QH/QH-Qc

Question 43

Corollaries of the Second Law for Refrigeration and Heat Pump Cycles 1. The coefficient of performance of an __________ refrigeration cycle is __________ than the coefficient of performance of a __________ refrigeration cycle when each operates between the same two thermal reservoirs. 2. _______ reversible refrigeration cycles operating between the same two thermal reservoirs have the _______ coefficient of performance.

Answer 43

* Irreversible * Always Less * Reversible * All * Same

Question 43

Maximum Performance Measures for Cycles Operating Between Two Reservoirs

Answer 43

* The discussion continues in this section with the development of expressions for the maximum thermal efficiency of power cycles and the maximum coefficients of performance of refrigeration and heat pump cycles in terms of reservoir temperatures evaluated on the Kelvin scale. * These expressions can be used as standards of comparison for actual power, refrigeration, and heat pump cycles.

Question 43

Thermal efficiency of a system undergoing a reversible power cycle while operating between thermal reservoirs at temperatures 𝑇𝐻 and 𝑇𝐶 . (Carnot Efficiency)

Answer 43

nmax = 1 - Tc/TH * The value of the Carnot efficiency increases as 𝑻𝑯 increases and/or 𝑻𝑪 decreases.

Question 44

Coefficient of performance of any system undergoing a reversible refrigeration cycle while operating between the two reservoirs:

Answer 44

Bmax = TC/TH-TC * Note that the temperatures used to evaluate βmax and γmax must be absolute temperatures on the Kelvin or Rankine scale.

Question 45

Coefficient of performance of any system undergoing a reversible heat pump cycle while operating between the two reservoirs

Answer 45

ymax = TH/TH-TC * Note that the temperatures used to evaluate βmax and γmax must be absolute temperatures on the Kelvin or Rankine scale.

Question 46

The _________________ of the refrigerator is __________ for a reversible refrigeration cycle operating between reservoirs at the same two temperatures. That is, __________ are present within the system.

Answer 46

* Coefficient of Performance * Less Than * Irreversible

Question 47

Carnot Cycle In a Carnot cycle, the system executing the cycle undergoes a series of four internally reversible processes

Answer 47

* Two adiabatic processes * Alternated with two isothermal processes. * An ideal reversible closed thermodynamic cycle

Question 48

The four processes of the cycle are: Process 1–2: The gas is compressed ____________ to state 2, where the temperature is TH. Process 2–3: The assembly is placed in contact with the reservoir at TH . The gas expands ______________ while receiving energy QH from the hot reservoir by heat transfer. Process 3–4: The assembly is again placed on the insulating stand and the gas is allowed to continue to expand _____________ until the temperature drops to TC. Process 4–1: The assembly is placed in contact with the reservoir at TC. The gas is compressed _____________ to its initial state while it discharges energy QC to the cold reservoir by heat transfer.

Answer 48

* Process 1-2: Adiabatically (Adiabatic Compression) * Process 2-3: Isothermally (Isothermal Expansion) * Process 3-4: Adiabatically (Adiabatic Expansion) * Process 4-1: Isothermally (Isothermal Compression)