Physics
Energy Dissipation
Energy dissipation refers to the process by which energy is transformed from one form to another and eventually lost as heat. This occurs when energy is transferred from a system to its surroundings, resulting in a decrease in the system's total energy. Energy dissipation is an important concept in physics, as it plays a role in many natural phenomena and technological applications.
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6 Key excerpts on "Energy Dissipation"
eBook - PDF- Marco Aurélio dos Santos Bernardes(Author)
- 2011(Publication Date)
- IntechOpen(Publisher)
Therefore, we anticipate that the concepts of entransy and entransy dissipation may help us to gain more profound insight on thermodynamics in particular and on science in general. 2. The application of entransy dissipation theory in heat convection In this section, the entransy dissipation theory developed in Section 1 are applied to analyze the heat convection. 2.1 Introduction The entropy and entropy generation can help us to deeply understand the momentum and heat transfer (Bejan, 1982; Herwig, 2010). Bejan (1982) realized that in order to improve the performance of the heat transfer enhancement or thermal insulation equipments, one need to reduce the entropy generation rate. Similarly, according to the definition of entransy dissipation given in Section 1.3, it is required to minimize the entransy dissipation rate for achieving the best heat transfer enhancement and thermal insulation. Therefore, it is of great value to derive the expression of the local rate of entransy dissipation rate for heat convection. Xu et al. (2009) have managed to get an expression of the local rate of entransy dissipation rate for heat convection. However, it lacks the theoretical basis in this derivation. In Section 2.2 with the help of the second law of thermodynamics in terms of entransy and entransy dissipation established in Section 1.3 we will make the derivation more rigorously. 2.2 Local thermodynamic entransy dissipation in heat convection The infinitesimal element as shown in Fig. 1 is an open thermodynamic system, where [ , ] T x y v v is the velocity, [ , ] T x y q q is the heat flux. For this system, we assume that the thermodynamic state is irrelevant with the position, but relevant with time. By the second law of thermodynamics for the open system expressed as Eqs.
- Roberto Villaverde(Author)
- 2009(Publication Date)
- CRC Press(Publisher)
These mechanical devices resist the motion and absorb or dissipate part of the energy transmitted to a structure during an earthquake by mechanisms that involve the yielding of metallic elements, sliding friction, the motion of a piston within a viscous fluid, or the deformation of viscoelastic materials. This design concept is based on the premise that earthquakes are a dynamic load and that the effect of dynamic loads on a system is reduced by the damping forces present in it. It implies, therefore, an increase in these damping forces through the addition of supplemental dampers or energy-absorbing devices to a level that would keep the structure and its nonstructural components virtually undamaged during a strong earthquake. Different from the base isolation concept, however, Energy Dissipation devices do not intercept the earthquake energy entering a structure. Instead, they allow the free transfer of this energy into the structure and partially dissipate it in the form of heat. Different from the base-isolation concept, too, these devices can be effective not only against earthquake ground motions but also against wind-induced vibrations. The incorporation of Energy Dissipation devices has for long been recognized as an effective means of controlling excessive vibration in mechanical systems, with the use of shock absorbers in motor vehicles being perhaps the best-known example. The purpose of this chapter is to describe the basic concepts behind the supplemental Energy Dissipation technology. First, a review on the influence damping has in the dynamic behavior of structures and the physical consequences of adding Energy Dissipation devices to a structure is presented. Then, a description of some of the most commonly used Energy Dissipation devices is given. Specifically, friction, viscoelastic, fluid, and hysteretic dampers are described. Thereafter, a description of the techniques that may be used to model and analyze structures with added energy
- Michael M. Khonsari, Mehdi Amiri(Authors)
- 2012(Publication Date)
- CRC Press(Publisher)
For example, in dealing with plastic deformation of solids, the density of dislocations is identified as an internal variable. Other examples of internal variables can be found in Lebon, Jou, and Casas-Vazquez. From the foregoing discussion, it can be concluded that to characterize irreversible pro-cesses, the specific free energy should be supported with a complementary function which takes into account the effect of, for example, internal variable, plastic deformation, and heat conduction. The complementary function is represented by the dissipation potential , Φ , as a measure of exhaustion of the system’s lifespan. Note that the dissipation function is not a state function. Unlike the free energy function, which describes only the initial and final states of the system, Φ describes the evolution of the system during the process. Therefore, for a given system, Φ depends on the process path. Consider, for example, a solid block sliding a distance ∆ x on a surface with velocity, V, as shown in Figure 3.2. The dissipative process in sliding is friction and the amount of work during the process is ∆ W = – F f ∆ x (3.2) where the negative sign means the direction of the friction force is opposite to that of the sliding. The rate of Energy Dissipation during sliding, ∆ W/ ∆ t, is Φ = Δ Δ = -Δ Δ = ⋅ W t F x t F V f f (3.3) It can be seen from Equation (3.3) that the dissipation function during this sliding friction process is defined as the inner product of two vectors: the nonconservative friction force, F f , and the rate of a time-dependent kinematical parameter, ∆ x/ ∆ t . The product defines the dissipation of energy. This example shows that, in general, it is possible to define the dissipation function as the product of the dissipative forces and the rate of kinematic parameters.
- Jonathan Wickert, Jonathan Wickert, Kemper Lewis(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
We took a very similar viewpoint in Chapter 4 when we used free body diagrams to examine forces acting on structures and machines. In that case, all forces that crossed an imaginary boundary drawn around the body were included on the diagram, and other effects were disregarded. In much the same way, engineers analyze thermal and energy systems by isolating a system from its surroundings and identifying heat that flows into or out of the system, work that is performed on the surroundings (or vice versa), and potential or kinetic energy levels that change within the system. At a high level of abstraction, consider the thermal and energy system sketched in Figure 7.8. The quantity of heat Q , which may have been produced by burning a fuel, flows into the system. The heat can be transferred by the processes of conduction, convection, or radiation. At the same time, the system performs mechanical work W as an output. In addition, it is possible that the internal energy of the system changes by the amount labeled as D U in Figure 7.8. The internal energy change could correspond to the temperature of the system being raised (in which case thermal energy is stored), to its kinetic energy ( U k ) changing, or to changes in its gravitational ( U g ) or elastic ( U e ) potential energy. The first law of thermodynamics states that these three quantities balance according to Q 5 W 1 D U (7.9) System First law of thermodynamics Heat supplied to the system, Q Work performed by the system, W System Surroundings Internal energy change D U Figure 7.8 Schematic of the first law for energy balance in a thermal and energy system. Copyright 201 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience.
- Jonathan Wickert, Kemper Lewis, Jonathan Wickert(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
We took a very similar viewpoint in Chapter 4 when we used free body diagrams to examine forces acting on structures and machines. In that case, all forces that crossed an imaginary boundary drawn around the body were included on the diagram, and other effects were disregarded. In much the same way, engineers analyze thermal and energy systems by isolating a system from its surroundings and identifying heat that flows into or out of the system, work that is performed on the surroundings (or vice versa), and potential or kinetic energy levels that change within the system. At a high level of abstraction, consider the thermal and energy system sketched in Figure 7.8. The quantity of heat Q, which may have been produced by burning a fuel, flows into the system. The heat can be transferred by the processes of conduction, convection, or radiation. At the same time, the system performs mechanical work W as an output. In addition, it is possible that the internal energy of the system changes by the amount labeled as DU in Figure 7.8. The internal energy change could correspond to the temperature of the system being raised (in which case thermal energy is stored), to its kinetic energy (U k ) changing, or to changes in its gravitational (U g ) or elastic (U e ) potential energy. The first law of thermodynamics states that these three quantities balance according to Q 5 W 1 DU (7.9) System First law of thermodynamics Heat supplied to the system, Q Work performed by the system, W System Surroundings Internal energy change DU Figure 7.8 Schematic of the first law for energy balance in a thermal and energy system. Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience.
eBook - PDFThermodynamics
Concepts and Applications
- Stephen R. Turns(Author)
- 2006(Publication Date)
- Cambridge University Press(Publisher)
FIGURE 4.2 Energy storage in the vibrating lattice of a solid. formal definition of heat [2] is the following: Heat is energy transferred, without transfer of mass, across the boundary of a system (or across a control surface) because of a temperature difference between the system and the surroundings or a temperature gradient at the boundary. Because of the importance of this definition, let us elaborate some of the important implications: First, heat occurs only at the boundary of a system; that is, it is a boundary phenomenon. As a consequence, a system cannot contain heat. The addition of heat to a system with all else held constant, however, increases the energy of a system, and, conversely, heat removal from a system decreases the energy of a system. Another important element in this definition of heat is that the “driving force” for this energy exchange is a temperature difference or temperature gradient. Other energy transfers across a system boundary may occur, but only heat is controlled solely by a temperature difference. We can gain some physical insight into this boundary energy exchange by examining the molecular processes involved. The energy exchange proper is carried out by the collision of molecules in which the higher kinetic energy molecules, in general, impart some of their energy to the lower kinetic energy molecules. Because the higher kinetic energy molecules are at a higher temperature than the lower energy molecules, the direction of the energy exchange is from high temperature to low temperature. A more rigorous treatment of this process would involve the subject of irreversible thermodynamics [5–7] and is beyond the scope of this book. Semantics In spite of our attempts here to be very precise about the definition of heat, some semantic problems arise out of traditions and nomenclature developed prior to the advent of modern thermodynamic principles. Specifically, in the common term heat transfer, the word transfer is redundant.
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