Non-Flow Processes

8 Key excerpts on "Non-Flow Processes"

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  General Thermodynamics

  • Donald Olander(Author)
  • 2007(Publication Date)
  • CRC Press

    (Publisher)

  Although never completely attainable, nearly isentropic processes are of enormous practical importance. The passage of steam through a well-designed turbine or the flow of a liquid through an efficient pump represent processes that are close to isentropic, or its synonym, adiabatic-reversible. • Cyclical processes are combinations of “one-way” processes such as those described above that return the system to its original state. The path followed by the working fluid in an electric power plant or in a refrigerator or air conditioner are common cyclical processes. 16 General Thermodynamics Figure 1.10 illustrates the above processes on a process diagram . Its coordinates are pressure and temperature, although any other pair of thermodynamic properties would do equally well. The arrows represent processes and the numbers represent thermodynamic states. The process 1 → 2 is isothermal, and is followed by an isobaric process 2 → 3. If the substance involved in these processes is an ideal gas, the process 3 → 4 is isochoric.* If the figure is closed by the dashed arrow, a cyclic process is produced. It is not necessary that the paths connecting the thermodynamic states (numbered corners) be straight lines. Nor is a sequence of connected processes necessary; the simplest process connects two states (points on a process diagram). 1.6 THERMODYNAMIC PROPERTIES Even pure substances possess a large number of quantitative properties, including electrical, magnetic, optical, mechanical, transport and thermodynamic. Only the last category is of interest here. Thermodynamic properties are sometimes called state functions because they depend only on the state or condition of the system. They do not depend on the process or the path by which the particular state was achieved. For example, water vapor at a specified pressure and temperature is the same whether created by evap-orating liquid water or by reacting H 2 and O 2 .

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  Advanced Thermodynamics

  • (Author)
  • 2014(Publication Date)
  • Library Press

    (Publisher)

  It is also worth noting that, for many systems, if the temperature is held constant then the internal energy of the system also is constant, and so Δ U = 0. From First Law of Thermodynamics, Q = Δ U + W , so it follows that Q = W for this same isothermal process. Applications Isothermal processes can occur in any kind of system, including highly-structured machines, and even living cells. Various parts of the cycles of some heat engines are carried out isothermally and may be approximated by a Carnot cycle. Phase changes, such as melting or evaporation, are also isothermal processes. Adiabatic process In thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which no heat is transferred to or from the working fluid. The term adiabatic literally means impassable, coming from the Greek roots ἀ - (not), δι ὰ - (through), and βα ῖ νειν (to pass); this etymology corresponds here to an absence of heat transfer. Conversely, a process that involves heat transfer (addition or loss of heat to the surroundings) is generally called diabatic . Although the terms adiabatic and isocaloric can often be interchanged, adiabatic processes may be considered a subset of isocaloric processes; the remaining complement subset of isocaloric processes being processes where net heat transfer does not diverge regionally such as in an idealized case with mediums of infinite thermal conductivity or non-existent thermal capacity. In an adiabatic irreversible process, dQ=0 is not equal to TdS (TdS>0). dQ=TdS=0 holds for reversible processes only. For example, an adiabatic boundary is a boundary that is impermeable to heat transfer and the system is said to be adiabatically (or thermally) insulated; an insulated wall approximates an adiabatic boundary. Another example is the adiabatic flame temperature, which is the temperature that would be achieved by a flame in the absence of heat loss to the surroundings.

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  Thermodynamics and Kinetics of Biological Processes

  • Ingolf Lamprecht, A. I. Zotin(Authors)
  • 2019(Publication Date)
  • De Gruyter

    (Publisher)

  Statistical Thermodynamics of Nonlinear Irreversible Processes F. M. Kuni, L. Z. Adjemian, A. P. Grinin, T. Yu. Novozhilova, B. A. Storonkin The thermodynamics of irreversible processes, as a science of general laws of energy, momentum and mass transfer, has appeared and developed mainly on the basis of phenomenological considerations of matter properties. The great achievements of nonequilibrium thermodynamics that made it one of the fundamental features of modern natural sciences are first of all due to the heuristic strength of the phenomenological approach. In the thermo-dynamics of irreversible processes, though, there are a number of important problems which seem to be, in principle, inaccessible to the phenomenologi-cal approach. Firstly, there is the basic problem of irreversibility. Within the phenomeno-logical approach irreversibility is introduced as a postulate. But can one formulate those conditions responsible for dissipation? The conditions under which irreversibility would, not only be consistent with, but follow from, the reversible character of the law of motion of individual particles in a thermodynamic system. Secondly, there is the problem of substantiations of a thermodynamic de-scription and defining the limits of its applicability. If a thermodynamic description proves insufficient and requires extension then the problem, naturally, develops into a more general one: how to choose additional variables so that they are independent of the thermodynamic ones. For example, what part of the tension tensor, independent of thermodynamic parameters should be introduced to describe highly viscous liquids (Kuni, 1974)? The problem becomes still greater when one has to transfer from the ordinary thermodynamics of nonlinear irreversible processes to an extreme nonequilibrium thermodynamics. To clarify this we should note that in © 1982 by Walter de Gruyter & Co., Berlin • New York Thermodynamics and Kinetics of Biological Processes

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  Fundamental of Ocean Dynamics

  • (Author)
  • 2011(Publication Date)
  • Elsevier Science

    (Publisher)

  CHAPTER 2 DYNAMICS, THERMODYNAMICS OF IRREVERSIBLE PROCESSES 2.1 THERMODYNAMIC PARAMETERS IN A NON-EQUILIBRIUM STATE Hitherto, only states of thermodynamic equilibrium have been considered when the internal state of a system is characterized completely by such param- eters as, for example, E , V, m, and mw. As it has been seen, for an equilib- rium state, one may introduce entropy 7) as a function of e, V, m, and m,. Further, changes of the function of state have been studied for transition from one equilibrium state to another (equilibrium processes) and condi- tions of thermodynamic equilibrium of a finite fluid volume have been derived. Next, non-equilibrium processes of transition in a fluid medium will be studied. In other words, a system will be investigated which is not in a state of thermodynamic equilibrium. Is it possible to use for this purpose the results of the thermodynamics of equilibrium states? Assume that the characteristic relaxation time of the system (time of tran- sition to an equilibrium state) decreases as the dimensions of the system decrease. Therefore subdivide this system into a set of somewhat small par- ticles (containing, however, a large number of molecules) in order that the relaxation time of each particle will be significantly shorter than the charac- teristic time scale of the process under consideration. Then it may be assumed in approximation that at any instant of time any particle finds itself in a state of thermodynamic equilibrium, and for each particle the entropy may be determined as an equilibrium function of its internal energy, volume and composition. After this, temperature, pressure, chemical potentials, etc., may be determined by ordinary means. In this manner, Gibbs’ relation proves to be valid for each particle and, consequently, also all formulae of equilibrium thermodynamics.

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  Physical Chemistry An Advanced Treatise

  • Wilhelm Jost(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  Chapter 2B Irreversible Processes A . SANFELD I. Introduction 217 I I . Conservation of Energy in Open Systems 218 I I I . Equality of Exchange Flow of Energy 219 IV. Entropy Production in O p e n Systems 221 V. Continuous Systems 225 V I . T r a n s p o r t and Chemical Equations 232 V I I . Stationary States 234 V I I I . Diffusion in Systems at Uniform T e m p e r a t u r e 235 I X . Diffusion in Systems at Nonuniform T e m p e r a t u r e 237 X . Electrokinetic Effects 239 X I . Entropy Production due to Viscosity 242 References 243 I. Introduction T h e thermodynamic properties of matter can be derived from two axioms (the two laws). However, the results of classical thermodynamics soon become too restrictive for the description of most real phenomena. Its main limitation lies in the fact that it can only describe equilibrium properties. In the classical reasoning, one has to suppose that the system goes from the initial to the final state through an infinite series of equi-librium states; it has to follow a reversible path. One may, of course, prove that such a path exists, but among the possible paths connecting the initial and the final states, the actual one followed by the system is certainly not the reversible one, which is a mere fiction. T h e overwhelming majority of phenomena at the macroscopic scale are irreversible. T h e true promoter of irreversible thermodynamics is De Donder 217 218 A. S a n f e l d (see De Donder and Van Rysselberghe (1936)). His main idea was that one could be able to go further than the usual statement of the second law, which is essentially an inequality (the entropy production can never be negative), and give an explicit quantitative evaluation of the entropy production. In the meantime, Onsager (1931) established his celebrated ' 'reciprocal relations'' connecting the coefficients which occur in the linear phenom-enological laws that describe irreversible processes.

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  Thermodynamics

  • James Luscombe(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  We’ll be guided by the use of balance equations, integral equations which account for the change, in time, in the amount of a quantity in a region of space. The equations of hydrodynamics follow from balance equations for mass, energy, and momentum, as we’ll show. We’ll establish a balance equation for entropy, where changes in entropy are controlled by the flow of mass, energy and momentum, and by the generation of entropy by irreversible processes. One of the goals of non-equilibrium thermodynamics is to identify the role of inhomogeneities in contributing to entropy creation. 14.1 Non-equilibrium processes Basic flow processes are described by phenomenological equations expressing a proportionality between fluxes and gradients. Familiar examples are Fourier’s law, a proportionality between heat flux J Q (units of W m - 2) and a temperature gradient, J Q = - κ ∇ T, where κ is the thermal conductivity (W K - 1 m - 1); Fick’s law, between a particle flux J n (m - 2 s - 1) and a concentration gradient, J n = - D ∇ n, where D is the diffusion coefficient (m 2 s - 1), and n is the particle density, number of particles per volume; Ohm’s law, between the electric current density J q (A m - 2) and the gradient of the electrostatic. potential, ϕ, J q = - σ ∇ ϕ, where σ is the electrical conductivity (S m - 1); and Newton’s law of viscosity, that the shear stress T xy (Pa) between adjacent layers in a fluid is proportional to a gradient of the velocity field, T xy = - ν ∂ v x / ∂ y, where ν is the viscosity (Pa s). These relations are summarized in Table 14.1. Table 14.1 Gradient-driven fluxes More complex phenomena arise when two or more of these basic effects are present simultaneously. In thermoelectricity, electrical conduction and heat conduction occur together. When a temperature gradient is set up, not only does heat flow but an electric field is created

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  Novel Thermal and Non-Thermal Technologies for Fluid Foods

  • PJ Cullen, Brijesh K. Tiwari, Vasilis Valdramidis(Authors)
  • 2011(Publication Date)
  • Academic Press

    (Publisher)

  In food capable of flowing, this requires the application of fundamental laws of conservation of mass, momentum, and energy, coupled with kinetic models describing biological reactions to inactivating agents (temperature and others involved in the particular processes). As a result, the reaction of the biotic matter dispersed in a fluid continuum can be resolved in time and space based on the mass, momentum, and energy transport (Hartmann and Delgado, 2005, Rauh et al., 2009 and Baars et al., 2007). Only in this way can a sufficiently exact figure of the effect of processing on the biomatter be achieved. The mere analysis of kinetic (only time-dependent) aspects of biochemical reactions in foods without consideration of the scale-dependent inhomogeneities and transport phenomena, leads to unacceptable simplifications and errors in evaluation of the impact of technological process on product quality. As a result, the non-uniform spatiotemporal distribution of processing parameters resulting in onset of over- and under-processed fractions is neglected. 2.2. Some Basic Considerations on Fluid Mechanics There is a large gap in the literature regarding a general overview of fluid mechanical, i.e. thermofluid-dynamical, effects on novel thermal and non-thermal processes. Particular processes such as high-pressure treatment and PEF are described in Gerlach et al. (2008), Krauss et al. (2010), Hartmann and Delgado (2005), Rauh et al. (2009), Baars et al. (2007), Otero et al. (2002), Kowalczyk et al. (2004), and Kowalczyk and Delgado (2007). The basis for the mathematical model applied for the analysis of transport phenomena in fluid matter are governing equations, which are usually formulated as partial differential conservation equations of mass, momentum, and energy, defined here for a Newtonian fluid with viscosity η(T, p) and density ρ(T, p)

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  Sustainable Process Engineering

  Prospects and Opportunities

  • Andrzej Benedykt Koltuniewicz(Author)
  • 2014(Publication Date)
  • De Gruyter

    (Publisher)

  Unit processes constitute the fundamental principles of process engineering. All processes in nature tend towards states of equilibrium but do not exist in equilibrium. Therefore the “distance” from equilibrium is the driving force of the process. Thermodynamic equilibrium – the term used in thermodynamics – refers to the state in which the macroscopic parameters, such as pressure, volume and all of the functions are constant over time. In a thermodynamic equilibrium there are no chemical reactions (chemical equilibrium), no macroscopic flow of particles, there are no unbalanced forces (mechanical equilibrium), and there is no flow of energy (thermal equilibrium). The “phase rule”, which was defined by Gibbs, applies to the state of thermodynamic equilibrium:

  (2.7)

  where: s – number of degrees of freedom, the number of intensive variables that can be changed without a qualitative change in the system (without changing the number of phases in equilibrium); α – the number of separate components, i.e., those which can be determined by means of chemical dependencies; f – the number of phases, and thus a homogeneous material chemically and physically (for example solution, gas phase, crystals of a specific composition).

  2.2.2 Conservation laws

  As previously mentioned each unit operation follows the same three primary physical laws which underlie chemical engineering design:

  1. conservation of mass;
  2. conservation of momentum;
  3. conservation of energy.

  The rate (kinetics) of flow and production of mass and energy is a key factor for the most economical operation and is based on principles of thermodynamics, reaction kinetics, fluid mechanics and transport phenomena. Unit processes are stationary if the incoming and outflowing streams are equal (see Fig. 2.3 ), and the process is independent of time. In nonstationary processes, there is accumulation. This also applies to all systems and subsystems.

  Fig. 2.3 . Graphical representation of the conservation law of mass and heat.

  Unit processes are stationary if the process is independent of time. Then, regardless of the system, which may be one device or a large technological system composed of multiple unit processes, the inflowing streams are balanced by the outflowing streams, and accumulation within any system is zero:

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