Thermodynamic Irreversibility Research Articles

The theory and practice of energy saving in the chemical industry: some methods for reducing thermodynamic irreversibility in chemical technology processes

The causes of thermodynamic irreversibility in chemical reactions and other industrial chemical processes (in particular absorption, stripping, and heat transfer) and ways of reducing energy consumption have been examined. Some thermodynamic principles based on the Second Law of thermodynamics such as the so called “counteraction principle,” “driving force method,” “quasi-static method,” and the result some of practical methods for energy saving design are discussed. It is demonstrated that the possibilities for reducing energy consumption are substantially higher than often seems possible. The correctness and practical effectiveness of the above methods have been confirmed by many commercial examples, for instance the lead author was able to reduce heat consumption in more than 20 commercial CO 2 removal installations by changes in networks only, without changing the absorbent. The heat consumption was reduced to about 1/2 to 1/3 of that used with conventional flow sheets.

Energy and Exergy Balance in the Process of Spray Combustion in a Gas Turbine Combustor

A theoretical model of exergy balance based on availability transfer and flow availability in the process of spray combustion in a gas turbine combustor has been developed to evaluate the total thermodynamic irreversibility and second law efficiency of the process at various operating conditions, for fuels with different volatilities. The velocity, temperature and concentration fields in the combustor, required for the evaluation of the flow availabilities and process irreversibilities, have been computed numerically from a two phase separated flow model of spray combustion. The total thermodynamic irreversibility in the process of spray combustion has been determined from the difference in the flow availability at inlet and outlet of the combustor. The irreversibility caused by the gas phase processes in the combustor has been obtained from the entropy transport equation, while that due to the inter-phase transport processes has been obtained as a difference of gas phase irreversibilities from the total irreversibility. A comparative picture of the variations of combustion efficiency and second law efficiency at different operating conditions for fuels with different volatilities has been made to throw light on the trade off between the effectiveness of combustion and the lost work in the process of spray combustion in a gas turbine combustor.

Integrative Thermodynamic Optimization of the Crossflow Heat Exchanger for an Aircraft Environmental Control System

This paper documents the process of determining the internal geometric configuration of a component by optimizing the global performance of the installation that uses the component. The example chosen is the crossflow heat exchanger used in the environmental control system of a modern aircraft. The optimization of global performance is achieved by minimizing the total entropy generation rate of the installation. There are three degrees of freedom in the heat exchanger configuration (the length-to-width and height-to-width aspect ratios, and the separator plate spacing ratio), which is subjected to two global constraints: total component volume, and total wall material volume (or weight/density) of wall material. Numerical results show how the optimal configuration responds to changes in specified external parameters such as volume, weight, Mach number, diffuser inlet cross-sectional area, and the pressure at which the cabin air is initially bled from the engine compressor. It is shown that the optimal configuration is robust and that major features such as the ratios of channel spacings and flow lengths are relatively insensitive to changes in some of the external parameters. It is also shown that the optimal heat exchanger geometry is insensitive to the thermodynamic irreversibility caused by discharging the used ram air into the ambient.

Thermodynamic irreversibilities and second law analysis in a spray combustion process

Thermodynamic irreversibilities and second law analysis in a spray combustion process

Irreversibility in a Reversible Lattice Gas

A simple lattice gas model, a microscopically reversible cellular automaton, is described and shown to exhibit thermodynamic irreversibility in processes similar to those in real gases. The model, which has no random elements, develops a long-lasting equilibrium state within a Poincare cycle. This state is an attractor resulting from the nonlinear nature of the collective particle collisions and motions. The results illustrate how the Second Law of Thermodynamics applies to real systems governed by reversible microscopic dynamics.

Thermodynamic optimization of heat-transfer equipment configuration in an environmental control system

In this paper, we show that many features of a heat transfer installation can be deduced from the maximization of the global performance of the greater system that employs the installation. The heat transfer installation is a series of two cross-flow heat exchangers. The greater system is the environmental control system (ECS) of an aircraft. The global performance objective is the minimization of the total thermodynamic irreversibility of the ECS. Several architectural features are deduced from principle: the relative position of the two heat exchangers, their relative sizes, and all the geometric aspect ratios of the two heat exchanger cores. We find that the optimized architecture is insensitive (robust) to changes in some of the external parameters. Robustness is a useful feature because it simplifies the design work. Furthermore, one design that is built can be expected to function at near-optimal levels when the external parameters change. The application of this method of topology optimization to more complex systems is discussed. Copyright © 2001 John Wiley & Sons, Ltd.

Nostack thermoacoustics

The ‘‘stack’’ used in conventional standing-wave thermoacoustics depends on intrinsic thermodynamic irreversibilities for its operation. One approach to increasing efficiency is to eliminate the stack, retaining a small gap between heat exchangers in a standing wave. While a ‘‘nostack’’ device has a temperature span that is limited by the achievable pressure amplitude, it is expected to have greatly increased thermodynamic efficiency compared to a stack-based device with the same power and operating temperatures. Losses associated with flow through the heat exchangers, however, are expected to be higher in a nostack device. The standard theory of low-amplitude thermoacoustics does not apply to nostack devices, where the displacement amplitude is larger than the heat exchangers and the gap. As an alternative, an idealized thermodynamic model of nostack is combined with separate calculations of conduction loss and flow losses, including so-called ‘‘minor losses’’ arising from sudden changes in cross-sectional flow area. The results suggest that by positioning the heat exchangers very close to a pressure antinode to reduce flow velocity, efficiencies similar to Stirling-like thermoacoustic devices might be achieved with the nostack idea. [Work supported by the Office of Naval Research and the Pennsylvania Space Grant Consortium.]

A study on the performance of multi-stage condensation heat pumps

In this study, computer simulation programs were developed for multi-stage condensation heat pumps and their performance was examined for CFC11, HCFC123, HCFC141b under the same condition. The results showed that the coefficient of performance (COP) of an optimized ‘non-split type’ three-stage condensation heat pump was 25–42% higher than that of a conventional single-stage heat pump. The increase in COP differed among the fluids examined. The improvement in COP was due largely to the decrease in average temperature difference between the refrigerant and water in the condensers, which resulted in a decrease in thermodynamic irreversibility. For the three-stage heat pump, the highest COP was achieved when the total condenser area was evenly distributed to the three condensers. For the two-stage heat pump, however, the optimum distribution of total condenser area varied with working fluids. For the three-stage system, splitting the condenser cooling water for the use of intermediate and high pressure subcoolers helped increase the COP further. When the individual cooling water for the intermediate and high pressure subcoolers was roughly 10% of the total condenser cooling water, the optimum COP was achieved showing an additional 11% increase in COP as compared to that of the ‘non-split type’ for the three-stage heat pump system.

Correlation functions for glass-forming systems

We present a simple, linear, partial-differential equation for the density-density correlation function in a glass-forming system. The equation is written down on the basis of fundamental and general considerations of linearity, symmetry, stability, thermodynamic irreversibility and consistency with the equation of continuity (i.e. , conservation of matter). The dynamical properties of the solutions show a change in behavior characteristic of the liquid-glass transition as a function of one of the parameters (temperature). The equation can be shown to lead to the simplest mode-coupling theory of glasses and provides a partial justification of this simplest theory. It provides also a method for calculating the space dependence of the correlation functions not available otherwise. The results suggest certain differences in behavior between glassy solids and glass-forming liquids which may be accessible to experiment. A brief discussion is presented of how the method can be applied to other systems such as sandpiles and vortex glasses in type II superconductors.

Synthesis of Single Effect Solid-Gas Thermochemical Refrigerators

A systematic approach to the energy efficient design of single effect solid-gas Thermochemical Refrigerators (TR) using the appropriate choice of salt materials is proposed. The approach includes three major steps. The first one, the targeting step, is applied to the ideal thermochemical process. It allows identification of the energy performance targets (the ideal Coefficient of Performance, COP i ) as a function of external temperature conditions and the internal distribution of energy flows within a thermochemical system. Targets can be set without actually having to carry out the design of the system. This step characterizes only the thermodynamic feasibility of an ideal thermochemical process. A new graphical technique, a modified Carnot factor vs. heat diagram, is applied to determine the targets. In the second step, in order to achieve the targeted COP i value, the design options of ideal thermochemical systems using different salt materials are generated. The physicochemical feasibility of the options is ensured in this step on the Clausius–Clapeyron diagram. Finally, in the third step, the assessment of the thermodynamic irreversibilities produced within real thermochemical processes using the same materials as the ideal ones allows evaluation of the real COP values. This step is the traditional energy and exergy analysis that ensures the thermodynamic feasibility of the real thermochemical systems.

Irreversible statistical mechanics from reversible motion: Q2R automata

Q2R cellular automata are a nice pedagogical example for addressing a century-old question discussed at the 20th IUPAP Statistical Physics Conference in Paris last July: How is thermodynamic irreversibility, as seen in entropy increase, compatible with microscopic reversibility, as in Newton's equations of motion? The Boltzmann–Zermelo argument says that the times for returning to the low-entropy initial state of a large system are far longer than the age of the universe. How can we test this assertion? Molecular dynamics in its usual form is inadequate to address this question, since arithmetic rounding errors as well as discretization of space and time preclude return to the exact initial configuration. Monte Carlo simulations of Ising models avoid such errors but require random numbers and are therefore not reversible in the usual sense. The Q2R update rules of cellular automata for microcanonical Ising models are reversible and the system returns exactly to the initial configuration after an exponentially long time. Computer simulation of Q2R cellular automata help us to understand some very old fundamental problems. This property will be reviewed, as well well as unexplained critical exponents obtained in large-scale simulations.

Action-Type Variational Principles For Hyperbolic and Parabolic Heat & Mass Transfer

For the field or Eulerian description of heat conduction, a method is discussed associated with description of thermal fields by a variational principle involving suitably constructed potentials rather than original physical variables. The considered processes are: simple hyperbolic heat transfer and coupled parabolic transfer of heat, mass and electric charge. By using various gradient or nongradient representations of original physical fields in terms of potentials, which are quantities of similar sort as those which Clebsch used in his representation of hydrodynamic velocity, suitable action-type criteria can be found, and corresponding Lagrangian and Hamiltonian formalisms can be developed. Symmetry principles can also be considered and components of energy-momentum tensor can be evaluated for a gauged lagrangian. The limiting reversible case appears as a suitable reference frame. The results suggest that thermodynamic irreversibility does not change neither kinetic potential nor action functional; it only complicates potential representations of physical fields in comparison with those describing the reversible evolution.

Thermodynamic Irreversibility from High-Dimensional Hamiltonian Chaos

This paper discusses the thermodynamic irreversibility realized in high-dimensional Hamiltonian systems with a time-dependent parameter. A new quantity, the irreversible information loss, is defined from the Lyapunov analysis so as to characterize the thermodynamic irreversibility. It is proved that this new quantity satisfies an inequality associated with the second law of thermodynamics. Based on the assumption that these systems possess the mixing property and certain large deviation properties in the thermodynamic limit, it is argued reasonably that the most probable value of the irreversible information loss is equal to the change of the Boltzmann entropy in statistical mechanics, and that it is always a non-negative value. The consistency of our argument is confirmed by numerical experiments with the aid of the definition of a quantity we refer to as the excess information loss.

Let us keep our ontology and epistemology separate!

Gold & Stoljar are right in their thesis but incomplete in not pointing out that there are many other arguments from cognate sciences suggesting that a radical eliminativist neuroreductionism is unlikely to be achieved. The radical neuron doctrine they criticize is only a hoped for dogma that cannot be verified, whereas a constrained monistic materialism (with only partial reductionism) is subject to immediate test by applying such criteria as combinatorial complexity and thermodynamic irreversibility.

Thermodynamic Irreversibilities and Second Law Analysis in a Spray Combustion Process

A theoretical model of exergy analysis, based on availability transfer and flow availability, in the process of spray combustion has been developed to evaluate the total thermodynamic irreversibility and second law efficiency of the process at various operating conditions. The velocity, temperature and concentration fields in the combustor, required for the evaluation of the availabilities and irreversibilities, have been computed numerically from a two phase separated flow model of the spray along with a suitable reaction kinetics for the gas phase reaction. The thermodynamic irreversibilities associated with the gas phase processes in the combustor have been obtained from the entropy transport equation, while that due to the interphase transport processes have been obtained as a difference of gas phase irreversibilities from the total irreversibility. The thermodynamic irreversibilities associated with different processes and a comparative picture of the variation of second law efficiency at various operating conditions have been made to throw light on the trade-off between the effectiveness of combustion and the lost work in a spray combustion process.

EXERGY ANALYSIS OF AMMONIA-BASED SOLAR THERMOCHEMICAL POWER SYSTEMS

The reversible dissociation of ammonia is one of the candidate reactions for use in closed loop solar thermochemical energy storage systems. The major determinant of achievable performance for such a system is the degree of thermodynamic irreversibility associated with the heat recovery process. Exergy analysis of a semi realistic 30 MPa isobaric system has revealed that the major irreversibilities occur within the exothermic reactor and the counterflow heat exchanger between ingoing and outgoing reactants. In this study, optimum reactor control yielded exergetic efficiencies up to 71%, which should translate to overall solar to electric conversion efficiencies of around 20%.

Interaction of catalase with cationic hydrogels: Influence of pH, kinetics of process and isotherms of adsorption

The adsorption interaction of catalase Penicillium vitale with cationic polymer hydrogels prepared from the vinyl ether of monoethanolamine was studied at various pHs of phosphate buffer solution, interaction times and enzyme concentrations. The hydrogels behaved as anion exchange swellable gel adsorbents. The formation of stable polymer–protein complexes with high enzymatic activity has been shown. The dependence of the interaction degree of protein macromolecules on swelling coefficients of gel has been found. The isotherms of protein adsorption indicate the thermodynamical irreversibility of the process. Copyright © 1999 John Wiley & Sons, Ltd.

Energy and exergy balance in a gas turbine combustor

An energy and exergy balance in the process of spray combustion in a model tubular gas turbine combustor has been made to determine the combustion efficiency and second law efficiency of the process at different operating conditions. The velocity, temperature and species concentration fields in the combustor have been evaluated numerically from a two-phase separated flow model of the spray along with suitable reaction kinetics for the gas phase reaction. A theoretical model of exergy analysis, based on availability transfer and flow availability, has been developed to predict the second law efficiency of the combustion process in the gas turbine combustor. A comparative picture of the functional relationships of combustion efficiency and second law efficiency of the process with the operating parameters of the combustor have been made to throw light on the trade-off between the effectiveness of combustion and the lost work due to thermodynamic irreversibility.

Chaos and irreversibility in simple model systems.

The multifractal link between chaotic time-reversible mechanics and thermodynamic irreversibility is illustrated for three simple chaotic model systems: the Baker Map, the Galton Board, and many-body color conductivity. By scaling time, or the momenta, or the driving forces, it can be shown that the dissipative nature of the three thermostated model systems has analogs in conservative Hamiltonian and Lagrangian mechanics. Links between the microscopic nonequilibrium Lyapunov spectra and macroscopic thermodynamic dissipation are also pointed out. (c) 1998 American Institute of Physics.

Relativistic Ornstein–Uhlenbeck Process

We wish to shed some light on the problem of thermodynamic irreversibility in the relativistic framework. Therefore, we propose a relativistic stochastic process based on a generalization of the usual Ornstein–Uhlenbeck process: we introduce a relativistic version of the Langevin equation with a damping term which has the correct Galilean limit. We then deduce relativistic Kramers and Fokker–Planck equations and a fluctuation-dissipation theorem is derived from them. Finally, numerical simulations are used to check the equilibrium distribution in momentum space and to investigate diffusion in physical space.