In this article we will consider thermodynamic processes. Let's get acquainted with their varieties and qualitative characteristics, and also study the phenomenon of circular processes that have the same parameters at the initial and final points.
Introduction
Thermodynamic processes are phenomena in which there is a macroscopic change in the thermodynamics of the entire system. 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 occurs is called the working body.
Based on the type of stability, one can distinguish between equilibrium and non-equilibrium. The equilibrium mechanism is a process in which all types of states 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 of a quasi-static nature.
Phenomenathermal type can be divided into reversible and irreversible thermodynamic processes. Reversible mechanisms are those in which the possibility is realized to carry out the process in the opposite direction, using the same intermediate states.
Adiabatic heat transfer
The adiabatic way of heat transfer is a thermodynamic process occurring on the scale of the macrocosm. Another characteristic is the lack of heat exchange with the space around.
Large-scale research into this process dates back to the beginning of the eighteenth century.
Adiabatic types of processes are a special case of the polytropic form. This is due to the fact that in this form the gas heat capacity is zero, which means it is a constant value. It is possible to reverse such a process 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 recognize adiabatic processes only in reversible ones.
Thermodynamic process of an ideal type gas in the form of an adiabatic phenomenon describes the Poisson equation.
Isochoric system
The isochoric mechanism 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.
Thermodynamic process of an ideal gas in isochoric form, allows moleculesmaintain proportions in relation to temperature. This is due to Charles' law. For real gases, this dogma of science does not apply.
Isobar system
The isobaric system is presented as a thermodynamic process that occurs in the presence of a constant pressure outside. I.p. flow at a sufficiently slow pace, allowing the pressure within the system to be considered constant and corresponding to the external pressure, can be considered reversible. Also, such phenomena include the case in which the change in the above-mentioned process proceeds at a low rate, which makes it possible to consider the pressure constant.
Perform I.p. possible in a system supplied (or removed) to the heat dQ. To do this, it is necessary to expand the work Pdv and change the internal type of energy dU, T.
e.dQ,=Pdv+dU=TdS
Changes in entropy level – dS, T – absolute value of temperature.
Thermodynamic processes of ideal gases in the isobaric system determine the proportionality of volume with temperature. Real gases will use up a certain amount of heat to make changes in the average type of energy. The work of such a phenomenon is equal to the product of external pressure and changes in volume.
Isothermal phenomenon
One of the main thermodynamic processes is its isothermal form. It occurs in physical systems, with a constant temperature.
To realize this phenomenonthe system, as a rule, is transferred to a thermostat, with a huge thermal conductivity. The mutual exchange of heat proceeds at a sufficient rate to overtake the rate of the process itself. The temperature level of the system is almost indistinguishable from the thermostat readings.
It is also possible to carry out the process of an isothermal nature using heat sinks and (or) sources, controlling the temperature constancy using thermometers. One of the most common examples of this phenomenon is the boiling of liquids under conditions of constant pressure.
Isentropic phenomenon
The isentropic form of thermal processes proceeds under conditions of constant entropy. Mechanisms of a thermal nature can be obtained using the Clausius equation for reversible processes.
Only reversible adiabatic processes can be called isentropic. The Clausius inequality states that irreversible types of thermal phenomena cannot be included here. However, the constancy of entropy can also be observed in an irreversible thermal phenomenon, if the work in the thermodynamic process on entropy is done in such a way that it is immediately removed. Looking at thermodynamic diagrams, lines representing isentropic processes can be referred to as adiabats or isentropes. More often they resort to the first name, which is caused by the inability to correctly depict the lines on the diagram characterizing the process of an irreversible nature. The explanation and further exploitation of isentropic processes are of great importance.value, as it is often used in achieving goals, practical and theoretical knowledge.
Isenthalpy type of process
Isenthalpy process is a thermal phenomenon observed in the presence of constant enthalpy. Calculations of its indicator are made thanks to the formula: dH=dU + d(pV).
Enthalpy is a parameter that can be used to characterize a system in which changes are not observed upon returning to the reverse state of the system itself and, accordingly, are equal to zero.
The isenthalpy phenomenon of heat transfer can, for example, manifest itself in the thermodynamic process of gases. When molecules, for example, ethane or butane, "squeeze" through a partition with a porous structure, and heat exchange between the gas and the heat around is not observed. This can be observed in the Joule-Thomson effect used in the process of obtaining ultra-low temperatures. Isenthalpy processes are valuable because they make it possible to lower the temperature within the environment without wasting energy.
Polytropic form
A characteristic of a polytropic process is its ability to change the physical parameters of the system, but leave the heat capacity index (C) constant. Diagrams that display 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 =const. P - pressure indicators, V - volumetric value of gas.
Process ring
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 a process that takes place in real thermal mechanisms that convert heat into mechanical work.
The working body is part of the components of each such machine.
A reversible thermodynamic process is presented as a cycle, which has paths both forward and backward. Its position lies in a closed system. The total coefficient of system entropy does not change with the repetition of each cycle. For a mechanism in which heat transfer occurs only between a heating or refrigeration 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 reservoir of heat is reached. 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 by a number of calculations and experiments that the reversible cycle has the highest degree of efficiency.
