Thermodynamic system
It uses the concept of thermodynamic processes, by which bodies pass from one equilibrium state to another by transfer of matter and energy between them.The term 'thermodynamic system' is used to refer to bodies of matter and energy in the special context of thermodynamics.Example theories and modeling approaches include the GENERIC formalism for complex fluids, viscoelasticity, and soft materials.For many non-equilibrium thermodynamical problems, an approximately defined quantity called 'time rate of entropy production' is very useful.Theoretical studies of thermodynamic processes in the period from the first theory of heat engines (Saadi Carnot, France, 1824) to the theory of dissipative structures (Ilya Prigozhin, Belgium, 1971) mainly concerned the patterns of interaction of thermodynamic systems with the environment.If the process of converting one type of energy into another takes place inside a thermodynamic system, for example, in chemical reactions, in electric or pneumatic motors, when one solid body rubs against another, then the processes of energy release or absorption will occur, and the thermodynamic system will always tend to a non-equilibrium state with respect to the environment.In isolated systems it is consistently observed that as time goes on internal rearrangements diminish and stable conditions are approached.Pressures and temperatures tend to equalize, and matter arranges itself into one or a few relatively homogeneous phases.A system in which all processes of change have gone practically to completion is considered in a state of thermodynamic equilibrium.[5][6][7] According to Bailyn, the commonly rehearsed statement of the zeroth law of thermodynamics is a consequence of this fundamental postulate.Non-equilibrium thermodynamics allows its state variables to include non-zero fluxes, which describe transfers of mass or energy or entropy between a system and its surroundings.[10][11][12][13][14] Often a wall restricts passage across it by some form of matter or energy, making the connection indirect.For example, in a reciprocating engine, a fixed wall means the piston is locked at its position; then, a constant volume process may occur.The walls of a closed system allow transfer of energy as heat and as work, but not of matter, between it and its surroundings.[22][23] Anything that passes across the boundary and effects a change in the contents of the system must be accounted for in an appropriate balance equation.Electrical energy travels across the boundary to produce a spark between the electrodes and initiates combustion.For infinitesimal changes the first law for closed systems may stated: If the work is due to a volume expansion byIn this case, the fact that the system is closed is expressed by stating that the total number of each elemental atom is conserved, no matter what kind of molecule it may be a part of.In the attempt to justify the postulate of entropy increase in the second law of thermodynamics, Boltzmann's H-theorem used equations, which assumed that a system (for example, a gas) was isolated.That is all the mechanical degrees of freedom could be specified, treating the walls simply as mirror boundary conditions.However, if the stochastic behavior of the molecules in actual walls is considered, along with the randomizing effect of the ambient, background thermal radiation, Boltzmann's assumption of molecular chaos can be justified.Isolated systems can exchange neither matter nor energy with their surroundings, and as such are only theoretical and do not exist in reality (except, possibly, the entire universe).By suitable thermodynamic operations, the pure substance reservoir can be dealt with as a closed system.Its internal energy and its entropy can be determined as functions of its temperature, pressure, and mole number.The intensive variable is called the chemical potential; for component substance i it is usually denoted μi.The theory can be generalized,[31][32][33] to consider any deviations from the equilibrium state, such as structure of the system, gradients of temperature, difference of concentrations of substances and so on, to say nothing of degrees of completeness of all chemical reactions, to be internal variables.are determined as The stationary states of the system exist due to exchange of both thermal energy (The sum of the last terms in the equations presents the total energy coming into the system with the stream of particles of substances.The middle terms in equations (2) and (3) depict energy dissipation (entropy production) due to the relaxation of internal variablesThis approach to the open system allows describing the growth and development of living objects in thermodynamic terms.
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