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THERMODYNAMICS > CHAPTER 5 > Flashcards

CHAPTER 5 Flashcards

1
Q

Considered to be the most fundamental law of science.

A

The Second Law of Thermodynamics

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2
Q

CP Snow in his Two Cultures wrote:

A

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

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3
Q

Einstein regarded Thermodynamics

A

“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.”

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4
Q

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

A

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

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5
Q

1st Aspects of the Second Law

A
  1. Predicting the direction of processes.
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6
Q

2nd Aspects of the Second Law

A
  1. Establishing conditions for equilibrium.
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7
Q

3rd Aspects of the Second Law

A
  1. Determining the best theoretical performance of cycles, engines, and other devices.
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8
Q

4th Aspects of the Second Law

A
  1. Evaluating quantitatively the factors that preclude the attainment of the best theoretical performance level.
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9
Q

5th Aspects of the Second Law

A
  1. Defining a temperature scale independent of the properties of any thermometric substance.
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10
Q

6th Aspect of the Second Law

A
  1. 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.

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11
Q

Three alternative statements of the second law of thermodynamics:

A
  1. Clausius statement
  2. Kelvin–Planck statement
  3. Entropy statement
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12
Q

Clausius Statement of the second law of thermodynamics

A

“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.

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13
Q

Kelvin–Planck Statement of the second law of thermodynamics

A

“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.”

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14
Q

Entropy Statement of the second law of thermodynamics

A

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

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15
Q

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

A

Rudolf Julius Emanuel Clausius

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16
Q

German Physicist and Mathematician

A

Rudolf Julius Emanuel Clausius

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17
Q

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

A

Rudolf Julius Emanuel Clausius

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18
Q

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

A

Thermal reservoir/ reservoir

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19
Q

Thermodynamic cycle

A

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

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20
Q

Analytical form of the Kelvin–Planck statement:

A

Wcycle ≤ 0 (Single Reservoir)

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21
Q

Lord Kelvin (1824-1907)

A

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

22
Q

Formulating the second law of thermodynamics

A

Lord Kelvin (1824-1907)

23
Q

Working to install telegraph
cables under the Atlantic.

A

Lord Kelvin (1824-1907)

24
Q

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’

A

Lord Kelvin (1824-1907)

25
Q

Max Karl Ernst Ludwig Planck

A

born in Kiel, Germany, on April 23, 1858

26
Q

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

A

Max Karl Ernst Ludwig Planck

27
Q

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.

A

Max Karl Ernst Ludwig Planck

28
Q

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

A

Entropy

29
Q

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

A

Entropy

30
Q

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

A

Closed System

31
Q

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

A

Produced

32
Q

Reversible process

A

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

33
Q

Irreversible process

A

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

34
Q

2 Types of Reversible Process

A
  1. Internally
  2. Externally

Both are Totally Reversible

35
Q

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.

A

Internally Reversable Process

36
Q

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.

A

Externally Reversible Process

37
Q

2 Types of Irreversible Process

A
  1. External irreversibilities
  2. Internal irreversibilities
38
Q

These are associated with dissipating effects outside the working fluid.

Example:
Mechanical friction occurring during a process due to some external source.

A

External Irreversibilities

39
Q

These are associated with dissipating effects within the working fluid.

Example:
Unrestricted expansion of gas, viscosity and inertia of the gas

A

Internal Irreversibilities

40
Q

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

A

n = Wcycle/QH = 1 - Qc/QH

41
Q

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

A

B = Qc/Wcycle =Qc/QH-Qc

42
Q

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

A

y = QH/Wcycle = QH/QH-Qc

43
Q

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.
A
  • Irreversible
  • Always Less
  • Reversible
  • All
  • Same
43
Q

Maximum Performance Measures for Cycles Operating Between Two Reservoirs

A
  • 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.
43
Q

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

A

nmax = 1 - Tc/TH

  • The value of the Carnot efficiency increases as 𝑻𝑯 increases and/or 𝑻𝑪 decreases.
44
Q

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

A

Bmax = TC/TH-TC

  • Note that the temperatures used to
    evaluate βmax and γmax must be
    absolute temperatures on the Kelvin or
    Rankine scale.
45
Q

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

A

ymax = TH/TH-TC

  • Note that the temperatures used to
    evaluate βmax and γmax must be
    absolute temperatures on the Kelvin or
    Rankine scale.
46
Q

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.

A
  • Coefficient of Performance
  • Less Than
  • Irreversible
47
Q

Carnot Cycle

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

A
  • Two adiabatic processes
  • Alternated with two isothermal processes.
  • An ideal reversible closed thermodynamic
    cycle
48
Q

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.

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

THERMODYNAMICS (2 decks)

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