Quasistatic and reversible processes thermodynamics. There is a second notion that is just as essential to thermodynamics and just as troublesome, yet it is largely overlooked. Explanation of classical and statistical thermodynamics, advantages and disadvantages of quasiequilibrium process, open and closed system, state postulate. An example of this is quasi static compression, where the volume of a system changes at a slow rate enough to allow the pressure to remain uniform and constant throughout the system. After the gas reaches equilibrium, the properties of gas are denoted by p 1. We were discussing various important topics such as quasi static or quasi equilibrium process, work and heat transfer in thermodynamics, enthalpy and specific heat of a substance in our recent posts.
For example, in equilibrium thermodynamics, a process is allowed to include even a violent explosion that cannot be described by non equilibrium thermodynamics. In thermodynamics, a quasistatic process is a thermodynamic process that happens slowly enough for the system to remain in internal equilibrium. As with all sciences, thermodynamics is concerned with the mathematical modeling of the real world. A quasistatic process is one that minimizes disequilibrium. It is necessary that a system be quasi equilibrium before applying many of the thermodynamics relations to that system. Recall that the relaxation time is the typical timescale for the system to return to equilibrium after being suddenly disturbed see sect. The thermodynamic state of a system is defined by specifying a set of measurable properties sufficient so. Explanation of classical and statistical thermodynamics, advantages and disadvantages of quasi equilibrium process, open and closed system, state postulate.
T is increased slowly from 0 to 100o c work cannot be calculated for an irreversible process. The thermodynamic equilibrium of the system is necessary for the system to have welldefined values of macroscopic properties such as the temperature and the pressure of the system at each instant of the process. Thermodynamics often consider a system evolving from an initial equilibrium state to a final equilibrium state thermodynamic transformationvia aa reversible transformation is a. Such a process is said to be quasi static for the system. That is, doing a quasi static process, we would have change in properties. Let us consider a system of gas contained in cylinder. Therefore, quasi static processes can be shown as welldefined paths in state space of the system. In studies of the conceptual foundations of thermodynamics, the perpetually troublesome notion of entropy attracts almost all the attention. When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times, it is called a quasi static or a quasi equilibrium process.
Basic concepts of thermodynamicspolytropic process,laws of. Combining nonequilibrium, quasiequilibrium, and equilibrium processes, we can rewrite 3 du s, v, n. During quasi static process system at every moment is infinitesimally near the state of thermodynamic equilibrium. In practice, a quasi static process must be carried out on a timescale which is much longer than the relaxation time of the system. Work requires unbalanced forcespressures mechanical equilibrium.
In practice, processes that are sufficiently slow and do not involve accelerated motion of the piston, large temperature. Show that for a quasistatic adiabatic process in a. The purpose of thermodynamics is to predict the equilibrium composition of a system from the properties of its components. A paddle wheel within the tank is rotated until the pressure inside rise to 150kpa. During the process 2kj of heat is lost to the surroundings. For example you can mix two gases very slowly quasistatic but you cant reverse that easily. This is the notion of thermodynamically reversible or quasi static processes. A process that can be made to reverse its direction of flow by changing the physical conditions and it is considered that there is no dissipation if energy. Jul 24, 2019 basic concepts of thermodynamics pdf polytropic process, laws of thermodynamics td, derivations for isobaric, isochoric, adiabatic and isothermal processes. A process is quasi equilibrium if the time rate of change of the process is slow relative to the time it takes for the system to reach thermodynamic equilibrium. As the name indicates that a process takes place in a system almost in equilibrium at every time is called a quasiequilibrium process. Sep 15, 2009 using theoretically quasi static andor reversible processes to stay pretty much at equilibrium.
Heat and thermodynamics notes for iit jee, download pdf. Along a quasi static path all intermediate states are equilibrium states thus from postulate i quasi static paths. The problem of equilibrium processes in thermodynamics. This is compounded by the profusion of overlapping and. A very slow process and the system is always maintained in the thermal equilibrium. Aug 20, 2019 the slow process in which all the states through which process passes are in equilibrium with one another. Suns heat causes the metal to expand slowly at a rate such that it cant be seen. Additionally, non equilibrium states cannot be dealt with using thermodynamic equations, so the approximation of quasi equilibrium allows thermodynamic processes to be understood. When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times, it is called a quasistatic or a quasiequilibrium process. Define quasistatic or quasiequilibrium process mechanical. Reversible process the temperature is changed very slowly so that the gas sample is at a uniform temperature. Quasistatic and reversible processes video khan academy. Equilibrium thermodynamics does, however, for theoretical development, use the idealized concept of the quasi static process. An equilibrium state will be occurring in every state which is passing through the system.
Quasistatic process an overview sciencedirect topics. Quasi equilibrium is an important concept for thermodynamics, because it is impossible for any real system to remain in true equilibrium while a process occurs. Phenomenological thermodynamics of quasiequilibrium and. In order that the mathematical deductions are consistent, we need some precise definitions of the basic concepts. This process is called quasi static process or quasi equilibrium process. A reversible process is a quasi equilibrium, or quasi static, process with a more restrictive requirement. Most introductory thermodynamics, physics and physical. Quasi static process or quasi equilibrium process in. In thermodynamics, a quasi static process is a thermodynamic process that happens slowly enough for the system to remain in internal equilibrium. In general, most of the engineering processes can be treated. During such slow processes, system is in quasiequilibrium because in the process the system. Quasi static process is an idealized concept and its conditions can never be rigorously satisfied in practice. Although, it is impossible to have a system in thermodynamic equilibrium when it undergoes a process but there is an assumption with some considerations in which a process can be occurred while maintaining system in thermodynamic equilibrium.
Heat transfer requires thermal disequilibrium temperature differences. Internal energy internal heat energy of a system is the sum of all the individual kinetic energies of motion and energies of interaction potential. The following is a discussion of some of the concepts we will need. If a process is carried out in such a way that at any time the system departs only infinitesimally from the equilibrium state it is called a quasi static process. Fulllibrary nothing is so practical as a good theory. Mechanical engineering thermodynamics lec 2, pt 5 of 5. Let us imagine that we have a box of gas, and we suddenly heat one wall of the box by pushing that wall up. All reversible processes are quasistatic processes but all quasistatic are not reversible.
What are the examples of quasistatic processes in our daily. Using theoretically quasistatic andor reversible processes to stay pretty much at equilibrium. Quasi static process pdf quasi static processes, zeroth law of thermodynamics and temperature. Can only relate work to system pressure for quasi static processes. Such a process, where system process in such a manner as studied above, will be termed as quasi static process or quasi equilibrium process in the field of thermal engineering. We will discuss difference between microscopic and macroscopic approach in thermodynamics in our next post. Statistical and classical thermodynamics, quasiequilibrium. All the concepts are explained below in a detailed way. A process is quasi equilibrium if the time rate of change of the process is slow relative to the time it takes for the. Real, irreversible, quasistatic, and reversible real irreversible quasistatic reversible partially quasistatic internally reversible quasistatic processes along a quasistatic path all intermediate states are equilibrium states.
Quasistatic process means very nearly static process. Internally reversible process the internally reversible process is a quasi equilibrium process, which, once having taken place, can be reversed and in so doing leave no change in the system. Its called quasistatic because if it were truly static it would mean there would be no temperature, pressure, etc. If you reach thermal equilibrium with untidy roommate. Pdf the problem of equilibrium processes in thermodynamics. On this diagram, the differential area da under the process curve in p. Due to the weight, the gas in cylinder is compressed.
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