{"id":17256,"date":"2018-03-19T07:39:32","date_gmt":"2018-03-19T07:39:32","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=17256"},"modified":"2022-11-10T12:28:31","modified_gmt":"2022-11-10T12:28:31","slug":"thermodynamic-processes","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/thermodynamic-processes\/","title":{"rendered":"Thermodynamic Processes"},"content":{"rendered":"
<\/div>\n
A thermodynamic process<\/strong> is defined as a change from one equilibrium macrostate to another macrostate. The initial<\/strong> and final states<\/strong> are the defining elements of the process.<\/div><\/div>\n

\"Thermodynamic<\/a> During such a process, \u00a0a system starts from initial state i<\/strong>, described by a pressure pi<\/sub><\/a><\/strong>, a volume Vi<\/sub><\/a><\/strong> and a temperature Ti<\/sub><\/a><\/strong>, passes through various quasi-static states<\/strong> to a final state f<\/strong>, described by a pressure pf<\/sub><\/strong>, a volume Vf<\/sub><\/strong>, and a temperature Tf<\/sub><\/strong>. In this process, energy<\/a> may be transferred from or into the system and can be done by or on the system. One example of a thermodynamic process is increasing the pressure of gas while maintaining a constant temperature. In the following section, examples of thermodynamic processes are of the highest importance in the engineering of heat engines<\/a>.<\/p><\/div><\/div>

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Types of Thermodynamic Processes<\/h2>\n<\/div><\/div>
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Reversible Process<\/h2>\n

In thermodynamics, a reversible process<\/strong> is defined as a process that can be reversed<\/strong> by inducing infinitesimal changes<\/strong> to some property of the system. In so doing, it leaves no change in either the system or surroundings. During the reversible process, the system\u2019s entropy<\/strong><\/a><\/b>\u00a0does not increase,<\/strong> and the system is in thermodynamic equilibrium<\/a> with its surroundings.

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Irreversible Process<\/h2>\n<\/p>

In thermodynamics, an irreversible process<\/strong> is defined as a process that cannot be reversed, which cannot return both the system and the surroundings to their original conditions.<\/p>\n

During irreversible process<\/strong> the entropy<\/strong><\/a> of the system increases<\/strong>.

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Cyclic Process<\/h2>\n<\/p>

A process that eventually returns a system to its initial state is called a cyclic process<\/strong>. After a cycle, all the properties have the same value they had at the beginning. For such a process, the final state<\/strong> is the same as the initial state<\/strong>, so the total internal energy<\/strong><\/a> change must be zero.<\/p>\n

It must be noted, according to the second law of thermodynamics<\/a><\/strong>, not all heat provided to a cycle can be transformed into an equal amount of work. Some\u00a0heat rejection<\/strong> must take place.\u00a0The thermal efficiency<\/strong><\/a>, \u03b7<\/em><\/strong>th<\/sub><\/em><\/strong>, of any heat engine as the ratio of the work<\/a> it does, W<\/strong>, to the heat<\/a> input at the high temperature, QH<\/sub>.\u00a0 \u03b7<\/em>th<\/sub><\/em>\u00a0= W\/QH<\/sub><\/strong>.<\/p><\/div><\/div>

\n

See also: Reversible Process<\/a><\/p>\n

See also: Irreversible Process<\/a><\/p>\n

See also: Cyclic Process<\/a><\/p>\n

\"Isentropic<\/a>
The isentropic process is a special case of adiabatic processes. It is a reversible adiabatic process. An isentropic process can also be called a constant entropy process.<\/figcaption><\/figure>\n
\"Cyclic<\/a>
A process that eventually returns a system to its initial state is called a cyclic process.<\/figcaption><\/figure>\n<\/div><\/div>
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Isentropic Process<\/h2>\n

An isentropic process<\/strong><\/a> is a thermodynamic process<\/strong>\u00a0in which the entropy<\/strong> <\/a>of the fluid or gas remains constant. It means the isentropic process<\/strong> is a special case of an adiabatic process<\/strong> in which there is no transfer of heat or matter. It is a reversible adiabatic process<\/strong>. An isentropic process<\/strong> can also be called a constant entropy process. In engineering, such an idealized process is very useful for comparison with real processes.<\/p>\n

See also: Isentropic Process<\/a>\u00a0

<\/span>Main characteristics of isentropic process<\/div>
\n
\"Isentropic<\/a>
Table of main characteristics<\/figcaption><\/figure>\n<\/div><\/div><\/div>
<\/div><\/p><\/div><\/div>
\n
\"P-V<\/a>
P-V diagram of an isentropic expansion of helium (3 \u2192 4) in a gas turbine.<\/figcaption><\/figure>\n<\/div><\/div>
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Adiabatic Process<\/h2>\n

An adiabatic process<\/strong><\/a> is a thermodynamic process<\/a>\u00a0in which there is no heat transfer<\/strong> into or out of the system (Q = 0). The system can be considered to be perfectly insulated<\/strong>. In an adiabatic process, energy is transferred only as work. The assumption of no heat transfer is very important since we can use the adiabatic approximation only in very rapid processes<\/strong>. There is not enough time for the transfer of energy as heat to take place to or from the system in these rapid processes.<\/p>\n

In real devices (such as turbines, pumps, and compressors), heat losses<\/strong> and losses in the combustion process occur. Still, these losses are usually low compared to overall energy flow, and we can approximate some thermodynamic processes by the adiabatic process.<\/p>\n

See also: Adiabatic Process<\/a>\u00a0

<\/span>Main characteristics of adiabatic process<\/div>
\n
\"Main<\/a>
Main characteristics of adiabatic process<\/figcaption><\/figure>\n<\/div><\/div><\/div>
<\/div><\/p><\/div><\/div>
\n
\"Isentropic<\/a>
Isentropic vs. adiabatic expansion.<\/figcaption><\/figure>\n<\/div><\/div>
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Isothermal Process<\/h2>\n

An isothermal process<\/strong><\/a> is a thermodynamic process<\/strong><\/a> in which the system\u2019s temperature<\/b>\u00a0remains constant<\/strong> (T = const). The heat transfer into or out of the system typically must happen at such a slow rate to continually adjust to the temperature of the reservoir through heat exchange. In each of these states, the thermal equilibrium<\/strong><\/a> is maintained.<\/p>\n

The case n = 1 <\/em><\/strong>corresponds to an isothermal<\/strong> (constant-temperature) process for an ideal gas and a polytropic process. In contrast to the adiabatic process<\/strong><\/a>, in which n = \u03ba<\/i><\/strong>\u00a0 and <\/em>a system exchanges no heat with its surroundings (Q = 0; <\/em>\u2206T\u22600<\/em>)<\/em>, in an isothermal process, there is no change in the internal energy (due to \u2206T=0) and therefore <\/em>\u0394U = 0 (for ideal gases) and Q \u2260 0.<\/em> An adiabatic process is not necessarily an isothermal process, nor is an isothermal process necessarily adiabatic.<\/p>\n

See also:\u00a0Isothermal Process<\/a>\u00a0

<\/span>Main characteristics of Isothermal process<\/div>
\n
\"Isothermal<\/a>
Isothermal process – main characteristics<\/figcaption><\/figure>\n<\/div><\/div><\/div>
<\/div><\/p><\/div><\/div>
\n
\"Boyle-Mariotte<\/a>
Boyle-Mariotte Law. For a fixed mass of gas at a constant temperature, the volume is inversely proportional to the pressure. Source: grc.nasa.gov NASA copyright policy states that \u201cNASA material is not protected by copyright unless noted\u201d.<\/figcaption><\/figure>\n<\/div><\/div>
<\/div>\n

Isobaric Process<\/h2>\n

An isobaric process<\/strong><\/a> is a thermodynamic process<\/a>\u00a0in which the pressure<\/strong><\/a> of the system remains constant<\/strong> (p = const). The heat transfer into or out of the system does work but also changes the internal energy of the system.<\/p>\n

Since there are changes in internal energy<\/a> (dU) and changes in system volume (\u2206V), engineers often use the enthalpy<\/strong><\/a> of the system, which is defined as:<\/p>\n

H = U + pV<\/strong><\/em><\/p>\n

In many thermodynamic analyses, it is convenient to use enthalpy<\/strong> instead of internal energy, especially in the first law of thermodynamics<\/strong><\/a>.<\/p>\n

In engineering, both important thermodynamic cycles (Brayton and Rankine cycle<\/strong>) are based on two isobaric processes<\/strong>. Therefore\u00a0the study of this process is crucial for power plants.<\/p>\n

See also: Isobaric Process<\/a>\u00a0

<\/span>Main characteristics of Isobaric Process<\/div>
\n
\"Isothermal<\/a>
Isothermal process – main characteristics<\/figcaption><\/figure>\n<\/div><\/div><\/div>
<\/div><\/p><\/div><\/div>
\n
\"Charles's<\/a>
For a fixed mass of gas at constant pressure, the volume is directly proportional to the Kelvin temperature. Source: grc.nasa.gov NASA copyright policy states that \u201cNASA material is not protected by copyright unless noted\u201d.<\/figcaption><\/figure>\n<\/div><\/div>
<\/div>\n

Isochoric Process<\/h2>\n

An isochoric process<\/strong> <\/a>is a thermodynamic process in which the volume<\/strong> of the closed system remains constant<\/strong> (V = const). It describes the behavior of gas inside the container that cannot be deformed. Since the volume remains constant, the heat transfer into or out of the system does not the p\u2206V work<\/a>\u00a0but only changes the system\u2019s internal energy<\/strong><\/a> (the temperature).<\/p>\n

In engineering internal combustion engines<\/strong>, isochoric processes are very important for their thermodynamic cycles (Otto and Diesel cycle). Therefore the study of this process is crucial for automotive engineering.<\/p>\n

See also:\u00a0Isochoric Process<\/a>\u00a0

<\/span>Main characteristics of Isochoric Process<\/div>
\n
\"Isochoric<\/a>
Isochoric process – main characteristics<\/figcaption><\/figure>\n<\/div><\/div><\/div>
<\/div><\/p><\/div><\/div>
\n
\"Guy-Lussac's<\/a>
For a fixed mass of gas at constant volume, the pressure is directly proportional to the Kelvin temperature.<\/figcaption><\/figure>\n<\/div><\/div>
<\/div>\n

Polytropic Process<\/h2>\n

A polytropic process<\/strong><\/a> is any thermodynamic process that can be expressed by the following equation:<\/span><\/strong><\/p>\n

pVn<\/sup> = constant<\/span><\/strong><\/em><\/p>\n

The polytropic process<\/strong> can describe gas expansion and compression, which include heat transfer<\/strong>. The exponent n<\/strong> is known as the polytropic index, <\/strong>and it may take on any value from 0 to \u221e, depending on the particular process.<\/p>\n

See also:\u00a0Polytropic Process<\/a>\u00a0

<\/span>Main characteristics of Polytropic Process<\/div>
\n
\"Polytropic<\/a>
Polytropic process – main characteristics<\/figcaption><\/figure>\n<\/div><\/div><\/div>
<\/div><\/p><\/div><\/div>
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\"polytropic<\/a>
Polytropic processes with various polytropic indexes.<\/figcaption><\/figure>\n<\/div><\/div>
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Throttling Process \u2013 Isenthalpic Process<\/h2>\n

A throttling process<\/strong><\/a> is a thermodynamic process<\/strong><\/a>\u00a0in which the enthalpy<\/strong><\/a> of the gas or medium remains constant (h = const)<\/strong>. The throttling process<\/strong> is one of the isenthalpic processes<\/strong>. During the throttling process, no work<\/strong> is done by or on the system (dW = 0), and usually, there is no heat transfer<\/strong> (adiabatic<\/strong>) from or into the system (dQ = 0). On the other, the throttling process cannot be isentropic. It is a fundamentally irreversible process<\/strong><\/a>. Characteristics of throttling process:<\/p>\n

    \n
  1. No Work Transfer<\/li>\n
  2. No Heat Transfer<\/li>\n
  3. Irreversible Process<\/li>\n
  4. Isenthalpic Process<\/li>\n<\/ol>\n

    Throttling of the wet steam<\/a> is also associated with the conservation of enthalpy<\/strong>. But in this case, a reduction in pressure<\/strong> causes an increase in vapor quality<\/strong>.<\/p>\n

    See also: Throttling Process<\/a><\/p><\/div><\/div>

    \"throttling<\/a><\/div><\/div>
    \u00a0
    <\/span>References:<\/div>
    Nuclear and Reactor Physics:<\/strong>\n
      \n
    1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading,\u00a0MA (1983).<\/li>\n
    2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.<\/li>\n
    3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.<\/li>\n
    4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering,\u00a0Springer; 4th edition, 1994, ISBN:\u00a0978-0412985317<\/li>\n
    5. W.S.C. Williams. Nuclear and Particle Physics.\u00a0Clarendon Press; 1 edition, 1991, ISBN:\u00a0978-0198520467<\/li>\n
    6. Kenneth S. Krane. Introductory Nuclear Physics, 3rd Edition, Wiley, 1987,\u00a0ISBN:\u00a0978-0471805533<\/li>\n
    7. G.R.Keepin. Physics of Nuclear Kinetics.\u00a0Addison-Wesley Pub. Co; 1st edition, 1965<\/li>\n
    8. Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.<\/li>\n
    9. U.S. Department of Energy, Nuclear Physics and Reactor Theory.\u00a0DOE Fundamentals Handbook,\u00a0Volume 1 and 2.\u00a0January\u00a01993.<\/li>\n<\/ol>\n

      <\/strong>Advanced Reactor Physics:<\/strong><\/p>\n

        \n
      1. K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.<\/li>\n
      2. K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.<\/li>\n
      3. D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.\u00a0<\/span><\/li>\n
      4. E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.<\/li>\n<\/ol>\n<\/div><\/div><\/div>