Transformation of energy

Thermal energy and combustion.
Effects of thermodynamics


Thermodynamic processes

Thermodynamic processes

In physics, the thermodynamic process is called the evolution of certain quantities (or properties) properly thermodynamic relative to a particular thermodynamic system. From the point of view of thermodynamics, these transformations must proceed from a state of initial equilibrium to a final one; that is, that the magnitudes that undergo a variation when passing from one state to another must be perfectly defined in said initial and final states.

In this way the thermodynamic processes can be interpreted as the result of the interaction of one system with another after being eliminated some ligature between them, so that finally the systems are in balance (mechanical, thermal and / or material) with each other.

In a less abstract way, a thermodynamic process can be seen as changes in a system, from initial conditions to other final conditions, due to its destabilization.

A thermodynamic system is in principle in a state of thermodynamic equilibrium when the main variables of the system (ie pressure, volume and temperature) do not experience any additional variation over time.

In the event that two or all of the above variables change (the variation of only one of them is impossible because they are all interconnected by an inverse or direct proportion ratio) we are in the presence of a thermodynamic transformation, which leads the system towards a another balance point.

The initial and final state of a transformation are identified by two pairs of values of the three quantities that define the state of a body: pressure, volume or temperature.

A thermodynamic transformation can take place:

  • Exchanging work, but without heat exchanges (for an adiabatic system: adiabatic transformation)
  • Exchanging heat, but without exchanging work; (for example, for an Isocora transformation)
  • Exchanging work and heat (for example, for an isobaric transformation or an isotherm)

A thermodynamic transformation can be reversible or irreversible. All real transformations are irreversible, since frictions can not be completely eliminated, so the condition of reversibility is only a theoretical approximation.

The most important processes of thermodynamic transformation are the following:

Isothermal processes

Isothermal processes are processes in which the temperature does not change.

An isothermal process is a transformation of a system in which the temperature remains constant: & Delta; T = 0. This happens when the system is in contact with an external source capable of exchanging heat with the system (yielding or providing heat) and the system evolves very slowly allowing the interior temperature to equalize the outside temperature (through the transmission of heat in the right direction: from the hottest part to the coldest).

In an adiabatic process, the exact opposite happens. There is no heat transmission (Q = 0).

Isobaric processes

Isobaric processes are processes in which the pressure does not vary. In other words, an isobaric process is a thermodynamic transformation that occurs at constant pressure.

When a perfect gas evolves isobarically from a state A to a state B, the associated temperature and volume follow Charles's law

Isochoric processes

Isochoric processes are processes in which the volume remains constant.

An isochoric process, also called isometric or isovolumic process is a thermodynamic process in which the volume remains constant. This implies that the process does not perform pressure-volume work.

Adiabatic processes

Adiabatic processes are processes in which there is no heat transfer.

An adiabatic process is one in which the system (generally, a fluid that does not exchange heat with its environment.) An adiabatic process that is, in addition, reversible, is an isentropic process.

The opposite end, in which the maximum heat transfer takes place, causing the temperature to remain constant, is called an isothermal process. The term adiabatic refers to elements that prevent the transfer of heat with the environment. An isolated wall is quite close to an adiabatic limit.

Another example is the adiabatic flame temperature, which is the temperature that a flame could reach if there was no loss of heat to the environment. In air conditioning, the processes of humidification (contribution of water vapor) are adiabatic, since there is no heat transfer, despite the fact that the air temperature and its relative humidity can be varied.

Adiabatic heating and cooling are processes that commonly occur due to the change in the pressure of a gas. This can be quantified using the law of ideal gases.

Diathermic processes

Diathermic processes are processes that allow heat to pass easily.

Isoentropic processes

Isentropic processes are adiabatic and reversible processes. Processes in which entropy does not vary.

In thermodynamics, an isentropic process, sometimes called an isentropic process, is one in which the entropy of the fluid that forms the system remains constant.

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Last review: January 2, 2018