In this article we will consider thermodynamic processes. We will get acquainted with their varieties and qualitative characteristics, and also study the phenomenon of circular processes that have the same parameters at the start and end points.
Introduction
Thermodynamic processes are called phenomena in which a macroscopic change in the thermodynamics of the entire system occurs. The presence of a difference between the initial and final state is called an elementary process, but it is necessary that this difference be infinitely small. The area of space within which this phenomenon takes place is called the working fluid.
By type of stability, one can distinguish between equilibrium and nonequilibrium. The equilibrium mechanism is a process during which all types of state through which the system flows are related to the equilibrium state. The implementation of such processes occurs when the change proceeds rather slowly, or, in other words, the phenomenon is quasistatic in nature.
The thermal type phenomenon can be divided into reversible and irreversible thermodynamic processes. Mechanisms are considered to be reversible, in which the ability to carry out the process in the opposite direction, using the same intermediate states, is realized.
Adiabatic heat transfer
The adiabatic path of heat transfer is a thermodynamic process occurring on a macrocosm scale. Another characteristic is the lack of heat exchange with the space around.
Large-scale research in the field of this process leaves the start of development in the early eighteenth century.
Adiabatic types of processes are a special case of a polytropic form. This is due to the fact that in this form the gas heat capacity is equal to zero, and therefore a constant value. A similar process can be reversed only if there is a point of equilibrium of all moments in time. Changes in the entropy index are not observed in this case or proceed too slowly. There are a number of authors who admit adiabatic processes only in reversible ones.
The thermodynamic process of an ideal type gas in the form of an adiabatic phenomenon describes the Poisson equation.
Isochoric system
The mechanism of the isochoric type is a thermodynamic process based on a constant volume. It can be observed in gases or liquids that have been sufficiently heated in a vessel with a constant volume.
The thermodynamic process of an ideal gas in an isochoric form allows molecules to maintain proportions in relation to temperature. This is subject to Charles's law. For real gases, this dogma of science is not applicable.
Isobaric system
The isobaric system is presented in the form of a thermodynamic process that occurs in the presence of constant pressure from the outside. Flow I.p. at a fairly slow pace, allowing the pressure within the system to be considered constant, and the corresponding indicator of external pressure can be considered reversible. Also to such phenomena can be attributed the case in which a change in the above-mentioned process proceeds at a low speed, allowing us to consider the pressure constant.
Implement I.p. it is possible in a system supplied (or diverted) to the heat dQ. For this, it is necessary to expand the work of Pdv and change the internal type of energy dU, T.
Changes in the entropy level - dS, T - absolute temperature value.
The thermodynamic processes of ideal gases in the isobaric system determine the proportionality of the volume with temperature. Real gases use a certain amount of heat to make changes in the average type of energy. The work of this phenomenon is equal to the indicator of the product of pressure from the outside, by changes in volume.
Isothermal phenomenon
One of the main thermodynamic processes is its isothermal form. It occurs in physical systems, with a constant temperature indicator.
To implement this phenomenon, the system, as a rule, is transferred to a thermostat, with a huge indicator of thermal conductivity. Mutual heat exchange proceeds at a sufficient speed to overtake the rate of the process itself. The temperature level of the system is almost no different from the thermostat.
It is also possible to carry out the process of isothermal nature using heat sinks and (or) sources, controlling the constancy of temperature using thermometers. One of the most common examples of this phenomenon is the boiling of liquids under constant pressure.
Isoentropic phenomenon
The isoentropic form of thermal processes proceeds under conditions of a constant value of entropy. Thermal mechanisms can be obtained using Clausius equality for reversible processes.
Only reversible adiabatic processes can be called isentropic. Clausius inequality claims that irreversible types of thermal phenomena cannot be related here. However, the constancy of entropy can also be observed with an irreversible thermal phenomenon, if the work in the thermodynamic process on entropy is carried out so that it is immediately removed. Looking at thermodynamic diagrams, lines representing isoentropic processes can be referred to as adiabats or isoentropes. They often resort to the first name, which is caused by the lack of the ability to correctly draw lines on a diagram characterizing an irreversible process. The explanation and further exploitation of isoentropic processes are of great importance, as it is often used in achieving goals, practical and theoretical knowledge.
Isoenthalpic type of process
The isoenthalpy process is a thermal phenomenon observed in the presence of enthalpy in a constant value. Calculations of its indicator are made thanks to the formula: dH = dU + d (pV).
Enthalpy is a parameter with which you can characterize a system in which changes are not observed when the system returns to the inverse state and, accordingly, are equal to zero.
The isoenthalpic heat transfer phenomenon can exemplify itself in the thermodynamic process of gases. When molecules, such as ethane or butane, “squeeze” through a porous septum, and heat exchange between gas and heat is not observed around. This can be observed in the Joule-Thomson effect used in the process of obtaining ultra-low temperature indicators. Isoenthalpic processes are valuable due to the fact that they make it possible to lower the temperature within the medium without wasting energy for this.
Polytropic form
A characteristic of the polytropic process is its ability to change the physical parameters of the system, but leave the heat capacity index (C) at a constant value. Diagrams depicting thermodynamic processes in this form are called polytropic. One of the simplest examples of reversibility is reflected in ideal gases and is determined using the equation: pV n = const. P - pressure indicators, V - volumetric value of gas.
The "ring" of the process
Thermodynamic systems and processes can form cycles that have a circular shape. They always have identical indicators in the initial and final parameters that evaluate the state of the body. Such qualitative characteristics include monitoring pressure, entropy, temperature, and volume.
The thermodynamic cycle finds itself in the expression of a model of the process occurring in real thermal mechanisms that turn heat into mechanical type work.
The working fluid is part of the components of each such machine.
A reversible thermodynamic process is presented in the form of a cycle, which has paths both in the direction straight and back. Its position lies in a closed type system. The total coefficient of systemic entropy during the repetition of each cycle does not change. In a mechanism in which heat transfer occurs only between a heating or refrigerating apparatus and a working fluid, reversibility is possible only during the Carnot cycle.
There are a number of other cyclic phenomena that can only be reversed when the introduction of an additional heat reservoir is achieved. Such sources are called regenerators.
An analysis of the thermodynamic processes during which regeneration occurs shows us that they are all common in the Reutlinger cycle. It has been proved in a number of calculations and experiments that a reversible cycle has the greatest degree of efficiency.