Technology & Engineering
Reversible Process
A reversible process in engineering refers to a system or operation that can be reversed without causing any net change in the system or its surroundings. It is a theoretical concept used to analyze the efficiency and performance of engineering systems, such as heat engines and refrigeration cycles. In a reversible process, the system undergoes changes in such a way that it can be returned to its original state with no net effect on the surroundings.
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10 Key excerpts on "Reversible Process"
eBook - PDF- Claus Borgnakke, Richard E. Sonntag(Authors)
- 2019(Publication Date)
- Wiley(Publisher)
A Reversible Process for a system is defined as a process that, once having taken place, can be reversed and in so doing leave no change in either system or surroundings. ......................................................................................................... .............. ....................................................... 152 CHAPTER FIVE THE SECOND LAW OF THERMODYNAMICS FIGURE 5.12 An example of an irReversible Process. Gas – Work Initial process Reverse process – Q Let us illustrate the significance of this definition for a gas contained in a cylinder that is fitted with a piston. Consider first Fig. 5.12, in which a gas, which we define as the system, is restrained at high pressure by a piston that is secured by a pin. When the pin is removed, the piston is raised and forced abruptly against the stops. Some work is done by the system, since the piston has been raised a certain amount. Suppose we wish to restore the system to its initial state. One way of doing this would be to exert a force on the piston and thus compress the gas until the pin can be reinserted in the piston. Since the pressure on the face of the piston is greater on the return stroke than on the initial stroke, the work done on the gas in this reverse process is greater than the work done by the gas in the initial process. An amount of heat must be transferred from the gas during the reverse stroke so that the system has the same internal energy as it had originally. Thus, the system is restored to its initial state, but the surroundings have changed by virtue of the fact that work was required to force the piston down and heat was transferred to the surroundings. The initial process therefore is an irReversible Process because it could not be reversed without leaving a change in the surroundings. In Fig. 5.13, let the gas in the cylinder comprise the system, and let the piston be loaded with a number of weights.
eBook - PDF- J Kestin(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
The processes which we encounter in real life are always irReversible Processes, processes during which disturbed equilibria are being equalized. Instead of using the term Reversible Process*' we can also speak of infinitely slow, quasi-static processes during which the system's capacity for performing work is fully utilized and no energy is dissipated. In spite of their not being real, Reversible Processes are most important in thermo-dynamics because definite equations can be obtained only by considering reversible changes; irreversible changes can only be described with the aid of inequalities when equilibrium thermodynamics is used. The actual criterion for a process to be reversible states that during its course there are no lasting changes of any sort in the surroundings if the process is allowed to go forward and then back to the original state. 1 + -= 1 . 6 6 1 + -= 1 . 4 0 5 '+! 1.33 3 5 6 20 THERMODYNAMICS. GENERAL CONSIDERATIONS 5. 1 A. THE REVERSIBLE ADIABATIC PROCESS The term adiabatic implies: exclusion of heat transfer to and from the body; in this connection the thermos flask invented by Dewar may be thought of. The opposite case is that of an isothermal process; in order to maintain the temperature it is necessary to allow heat to be transferred; in this connection one may imagine a water bath in which our quantity of gas is immersed. Consider a unit mass of a perfect gas and substitute dq = 0 du = c v dT into (4.2), taking into account (4.4). We then have (1) c v dT — -pdv. In order to transform this into a relation between v and p we use the equation of state (3.11 a). Instead of (1) we may write -~ c v ( p dv + v dp) + p dv = 0 re I c v H 1 p dv + c v v dp = 0 so that in view of (4.5) Cp pdv + c v vdp = 0, or, considering (4.14): ( 2 ) 7 + ^τ = ° We now assume γ to be a constant, see end of Sec. 4, so that we actually exceed the caloric assumption according to which u and hence c v , c p and γ depend on T alone.
eBook - PDFLectures on Theoretical Physics
Thermodynamics and Statistical Mechanics
- Arnold Sommerfeld, F. Bopp, J. Meixner, J. Kestin(Authors)
- 2012(Publication Date)
- Academic Press(Publisher)
The processes which we encounter in real life are always irReversible Processes, processes during which disturbed equilibria are being equalized. Instead of using the term “Reversible Process” we can also speak of infinitely slow, quasi-static processes during which the system’s capacity for performing work is fully utilized and no energy is dissipated. In spite of their not being real, Reversible Processes are most important in thermo-dynamics because definite equations can be obtained only by considering reversible changes; irreversible changes can only be described with the aid of inequalities when equilibrium thermodynamics is used. The actual criterion for a process to be reversible states that during its course there are no lasting changes of any sort in the surroundings if the process is allowed to go forward and then back to the original state. 20 THERMODYNAMICS. GENERAL CONSIDERATIONS A. T he r e v e r s i b l e a d i a b a t i c p r o c e s s The term adiabatic implies: exclusion of heat transfer to and from the body; in this connection the thermos flask invented by Dewar may be thought of. The opposite case is that of an isothermal process; in order to maintain the temperature it is necessary to allow heat to be transferred; in this connection one may imagine a water bath in which our quantity of gas is immersed. Consider a unit mass of a perfect gas and substitute dq = 0 du = cv dT into (4.2), taking into account (4.4). We then have (1) cv d T = -p dv. In order to transform this into a relation between v and p we use the equation of state (3.11 a). Instead of (1) we may write °v ( P dv + v dp) + pdv = 0 K ic· + f): j cv -j -----J p dv — )— cv v dp ■ so that in view of (4.5) Cp p dv + cv v dp = 0, or, considering (4.14): dp dv (2) 7 + > Ί γ = ° We now assume γ to be a constant, see end of Sec. 4, so that we actually exceed the caloric assumption according to which u and hence cv, cp and y depend on T alone.
No longer available |Learn more- Irving Granet, Maurice Bluestein(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
Reversible Process: Any process performed so that the system and all its surroundings can be restored to their initial states by performing the process in reverse. second law of thermodynamics: Heat cannot, of itself, pass from a lower temperature to a higher temperature. thermal efficiency: The ratio of the net work of a cycle to the heat added to the cycle. Equations Developed in This Chapter Net work output η = × net work output heat added 100 (4.1) Thermal efficiency η = -× = -× Q Q Q Q Q in r in r in 100 1 100 (4.2) Kelvin temperature function Q Q T T 1 2 1 2 = (4.6) Efficiency of a reversible cycle η = -× = -× T T T T T 1 2 1 2 1 100 1 100 (4.7a) Entropy ∆ ∆ S Q T s q T = = or Reversible Process (4.8) Entropy change s s c T T 2 1 2 1 -= ln (4.14) General property relation T s u p v J ∆ ∆ ∆ = + (4.16) General property relation T s h v p J ∆ ∆ ∆ = + (4.23) General property relation (SI) T ∆ s = ∆ h – v ∆ p (4.23a) Entropy increase principle ∆ S ≥ 0 for all isolated systems (4.24) QUESTIONS 4.1 Can a heat engine do anything other than deliver work? 4.2 Define a cycle. 4.3 Thermal efficiency is defined to be the ratio of net work to heat added in a cycle. Would you think that this is an appropriate definition to be used when a refrig-erator is being discussed? 175 The Second Law of Thermodynamics 4.4 Do you know of any process in nature that is reversible? 4.5 There are four distinct events that occur in the Carnot cycle. Starting with the heat reception event, name and describe each one. 4.6 There are three conclusions reached from the Carnot cycle regarding reversible cycles. What are they? 4.7 What was the contribution by Kelvin? 4.8 What two factors determine the limiting efficiency of any cycle? 4.9 How does the combination of the work of Kelvin and Carnot help in the design of power cycles? 4.10 The statement has been made that entropy is a property.
- S. Bobby Rauf(Author)
- 2021(Publication Date)
- River Publishers(Publisher)
The system and the surroundings can be restored to their initial states at the conclusion of a Reversible Process. No heat is wasted in a Reversible Process, there-fore, the machine or engine’s ef fciency is maximized. One of the attributes of a Reversible Process can be stated, math-ematically, as follows: Δ S = 0 IrReversible Process A thermodynamic process that is not reversible is referred to as an irReversible Process. In addition to the fact that heat is or can be wasted in an irrevers-ible process, there is a net change in entropy of the system. In other words: Δ S ≠ 0 | Irreversible Ideal Heat Engine, Ideal Heat Engine Cycle and Energy Flow Since the purpose of most engines is to convert one form of ener- 165 Thermodynamic Processes gy to another and perform work, an ideal heat engine’s function can be simplifed and understood through examination of heat/energy fow diagram in Figure 8-9. As depicted in Figure 8-9, a heat engine performs the conversion of heat energy to mechanical work, driven by the temperature gradient between the higher heat content heat source and a lower heat content point referred to as the heat sink. Ideal heat engine cycle and the fow of heat and energy in an ideal heat engine can be illustrated better through examination of the Heat Engine Energy Flow Diagram in Figure 8-9, and Heat Engine Pro-cess Flow Diagram in Figure 8-10, conjunctively. As the heat energy is transferred from the heat source to a heat sink, through a mechanical device, such as a turbine, a substantial por-Figure 8-9. Heat Engine Energy Flow Diagram Figure 8-10. Heat Engine Process Flow Diagram 166 Thermodynamics Made Simple for Energy Engineers tion of the heat energy is transformed into mechanical energy or work. This is analogous to the fow of electrical current in an electrical circuit where current is driven by the electromotive force, or voltage differ-ence between the positive terminal and the negative terminals of the voltage source.
eBook - ePubMaterials Kinetics
Transport and Rate Phenomena
- John C. Mauro(Author)
- 2020(Publication Date)
- Elsevier(Publisher)
For a system to undergo a Reversible Process, it must never leave equilibrium and must not increase the entropy of the universe. A Reversible Process should occur infinitely slowly and due to an infinitesimally small driving force. Owing to the infinitely slow nature of a Reversible Process, all of the changes that occur in the system are in thermodynamic equilibrium with each other. If the process is also adiabatic, i.e., if the heat content of the system remains constant during the process, then the Reversible Process is also isentropic, meaning that the entropy of the system itself also remains constant. The phenomenon of undergoing a Reversible Process is called reversibility. An example of a hypothetical Reversible Process is shown in Figure 2.1, where a gas is compressed by frictionless mechanical loading of sand, one grain at a time. The process is reversible because the perturbation of a single grain of sand is so small that the system can respond with an infinitesimally small change in its state, never leaving equilibrium. After the sand grains have compressed the gas, the process can be reversed by slowly removing each grain of sand, one at a time. The initial thermodynamic state of the universe is fully recovered after the grains of sand are removed. Of course, Reversible Processes primarily exist in a hypothetical ideal universe. In reality, nearly all processes are irreversible, where the initial state of the universe cannot be restored from the final state. During an irReversible Process, the various intermediate states of the system are not in equilibrium with each other. As a result, the entropy of the universe increases during an irReversible Process and cannot be restored to its initial value. The phenomenon of a system undergoing an irReversible Process is called irreversibility. An example of an irReversible Process is depicted in Figure 2.2, where a gas is compressed suddenly by dropping an anvil
eBook - PDF- R. Prasad(Author)
- 2016(Publication Date)
- Cambridge University Press(Publisher)
Introduction to the Thermodynamics of IrReversible Processes 12.0 Introduction It may be recalled that both classical and quantum thermodynamics consider systems in equilibrium, although theoretically the state of equilibrium takes an infinite time to reach. As such, the classical and quantum thermodynamics describe idealized systems that, in general, do not exist. The concept of reversibility is also very intimately related to the concept of equilibrium as any Reversible Process passes through a succession of equilibrium states. The fact is that most of the real life phenomenon are non-equilibrium processes and hence irreversible. The branch of science that deals with the flow of energy and mass or both of them between non-equilibrium systems via irreversible paths is called the thermodynamics of irReversible Processes. Now there are two possibilities: the non- equilibrium systems involved in the irReversible Processes are only marginally away from their equilibrium states or they are far away from their equilibrium states. In the former case the thermodynamics is called the linear thermodynamics of irReversible Processes while in the latter case it is termed as the non- linear thermodynamics of irReversible Processes. Before the modern tools of handling irReversible Processes were developed, the method for treating a general problem of thermodynamics was to separate out the truly reversible and irreversible components of the problem and work out the thermodynamics of the truly reversible component ignoring the irreversible component. In some cases both the truly reversible and the irreversible components were analyzed in the frame work of equilibrium thermodynamics. This methodology, though basically wrong, yielded correct results some times, but in some other cases it led to results that were not consistent with observations. However, need for a separate frame work for the treatment of irReversible Processes was felt even earlier, and it was L.
eBook - ePubApplied Thermodynamics
Availability Method And Energy Conversion
- Kam W. Li, KamW. Li(Authors)
- 2018(Publication Date)
- Routledge(Publisher)
Figure 2-3 indicates the difference between the reversible and irreversible heat transfer processes from body A to body B. While the actual heat transfer process is characterized by a finite temperature difference, the reversible heat transfer process is characterized by an infinite number of fictitious bodies between the actual bodies A and B, each fictitious body performing heat source and sink functions and reducing the temperature by an infinitesimal amount in the direction of heat flow. Like the quasi-static process, the reversible heat transfer process is an ideal process.Figure 2-3 Reversible and irreversible heat transfer processes: (a) irreversible heat transfer, (b) reversible heat transfer processFigure 2-4 shows a hot body being cooled in its environment. This actual heat transfer process is not reversible. To make the process entirely reversible, one can install a Carnot engine between the hot body and the environment. Because the Carnot engine is a reversible device, all processes in the Carnot system must be reversible. In other words, the hot body loses heat to its environment by δQh in a Reversible Process and, as a result, produces reversible work of δWc (i.e., Carnot work). If the hot body has a finite capacity and its temperature is decreased in the heat transfer process, one can make the process reversible by using an infinite number of Carnot engines between the hot body and its environment, one engine operating at a time and having the hot-body temperature reduced by an infinitesimal amount. The sum of all these Carnot engine outputs will be the reversible work in this process.Figure 2-4 Reversible and irreversible heat transfer process between a hot body and its environment.Figure 2-5(a) presents a typical heat exchanger in which heat is transferred from a high temperature stream to a low temperature stream. The heat transfer process can be made entirely reversible by placing an infinite number of Carnot engines between the streams. As shown in Fig. 2-5(b)
eBook - PDFThermodynamics
From Concepts to Applications, Second Edition
- Arthur Shavit, Chaim Gutfinger(Authors)
- 2008(Publication Date)
- CRC Press(Publisher)
237 10 Availability, Exergy, and Irreversibility The first law of thermodynamics constitutes a balance between the change of energy and the interactions of work and heat. From the point of view of the first law the two inter-actions are equivalent with no distinction between them. Hence, one cannot determine whether a process is efficient or not on the basis of the first law alone. In previous chapters we have seen that Reversible Processes do better thermodynami-cally than irReversible Processes. We have introduced the concept of isentropic efficiency to compare a real, adiabatic steady-state process, such as expansion in a turbine, with a reversible adiabatic process between the same pressures. The deviation of the isentropic efficiency from unity was considered a measure of the relative loss of work in the control volume. It may be questioned whether this is a good way of evaluating losses. For example, con-sider a steam turbine operating adiabatically between two given pressures, p 1 and p 2 . The lower the effectiveness, the higher the loss. One might believe that if the effectiveness of the turbine were zero, the loss would be complete, that is, all the potential for work would be lost. This chapter shows that such a statement is too simplistic and does not consider all the real loss aspects. Indeed, the steam at the exit of a turbine with zero effectiveness could still be used to produce work, albeit not directly in a turbine. This chapter deals with the thermodynamic limits of performance of a system between given end states, and introduces an alternative, more exact method, for evaluating losses in real processes based on the second law of thermodynamics. We define new concepts such as availability, exergy, and irreversibility that describe the ability of a system to pro-duce work, and provide a measure for the loss of this ability in real processes. We also offer a method for assessing the performance of a system based on exergy analysis.
eBook - PDF- William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
The entropy change of a system under a Reversible Process is given by ΔS = ∫ A B dQ/T . • A system’s change in entropy between two states is independent of the reversible thermodynamic path taken by the system when it makes a transition between the states. 4.7 Entropy on a Microscopic Scale • Entropy can be related to how disordered a system is—the more it is disordered, the higher is its entropy. In any irReversible Process, the universe becomes more disordered. • According to the third law of thermodynamics, absolute zero temperature is unreachable. CONCEPTUAL QUESTIONS 4.1 Reversible and IrReversible Processes 1. State an example of a process that occurs in nature that is as close to reversible as it can be. 4.2 Heat Engines 2. Explain in practical terms why efficiency is defined as W/Q h . 4.3 Refrigerators and Heat Pumps 3. If the refrigerator door is left open, what happens to the temperature of the kitchen? 4. Is it possible for the efficiency of a reversible engine to be greater than 1.0? Is it possible for the coefficient of performance of a reversible refrigerator to be less than 1.0? 4.4 Statements of the Second Law of Thermodynamics 5. In the text, we showed that if the Clausius statement is false, the Kelvin statement must also be false. Now show the reverse, such that if the Kelvin statement is false, it follows that the Clausius statement is false. 6. Why don’t we operate ocean liners by extracting heat from the ocean or operate airplanes by extracting heat from the atmosphere? 7. Discuss the practical advantages and disadvantages of heat pumps and electric heating. 8. The energy output of a heat pump is greater than the energy used to operate the pump. Why doesn’t this statement violate the first law of thermodynamics? 9. Speculate as to why nuclear power plants are less efficient than fossil-fuel plants based on temperature arguments. 10. An ideal gas goes from state ( p i , V i ) to state ( p f , V f ) when it is allowed to expand freely.
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