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1
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Nonequilibrium Reduced-Density Operator for Nanoscopic Systems

100%
Jacyna-Onyszkiewicz Z.
Acta Physica Polonica A
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2002
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vol. 102
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issue 6
717-727
EN
Retarded forms of the nonequilibrium reduced-density operator are derived from the generalized Schrödinger variational principle of a system with both mechanical and thermal perturbations, taking into account the additional condition that the values of generalized thermodynamic coordinates are fixed at infinitely remote past. This reduced density operator may be useful in describing nonequilibrium properties of nanoscopic and mesoscopic systems, as well as ultrathin films. With the help of this reduced-density operator the generalized Green-Kubo formulae are obtained.
2
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Endoreversible Four-Reservoir Chemical Potential Transformer with Diffusive Mass Transfer Law

100%
Xia D., Chen L., Sun F.
Acta Physica Polonica A
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2011
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vol. 120
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issue 3
378-383
EN
The performance of an isothermal endoreversible four-reservoir chemical potential transformer, in which the mass transfer between the mass reservoir and the working medium obeys diffusive law, is analyzed and optimized in this paper. The relation between the rate of energy pumping and the coefficient of performance of the isothermal chemical potential transformer is derived by using finite-time thermodynamics. Moreover, the optimal operating regions and the influences of some parameters on the performance of the cycle are studied. The results obtained herein can provide some new theoretical guidelines for the optimal design of a class of apparatus such as mass exchangers, as well as electrochemical, photochemical, and solid-state devices, and the fuel pumps for solar-energy conversion systems.
3
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Spin-1 Model of Noninteracting Nanoparticles

80%
Yalçin O., Erdem R., Övűnç S.
Acta Physica Polonica A
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2008
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vol. 114
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issue 4
835-844
EN
In this work, we presented a spin-1 model to investigate the magnetic properties of noninteracting monodomain nanoparticles based on the pair approximation. Nearest-neighbor pair interactions are incorporated between the Ising spins in three parts that are core, core-surface, and surface within the nanoparticle. Using the spin-1 Ising model of magnetization in the pair approximation, we calculated the free energy and minimized with respect to pair variables to obtain the field-cooled magnetization. Hysteresis loops of the system were plotted for various values of exchange coupling constants, and axial anisotropy of strength which couples the core, core-surface, and surface regions. The coercive field and its linear fit to the data were plotted as a function of radius of ferromagnetic nanoparticles.
4
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Power Optimization of a Miller Thermal Cycle with respect to Residual Gases and Equivalence Ratio

80%
Ebrahimi R.
Acta Physica Polonica A
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2013
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vol. 124
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issue 1
6-10
EN
The performance of an air standard Miller cycle is analyzed using finite-time thermodynamics. The relations between the power output and the compression ratio and between the power output and the thermal efficiency are derived by detailed numerical examples. The results show that, throughout the compression ratio range, the power output decreases with increasing residual gases. The results also show that if compression ratio is less than certain value, the power output decreases with increasing equivalence ratio, while if compression ratio exceeds certain value, the power output first increases and then starts to decrease with increasing equivalence ratio. The conclusions of this investigation are of importance when considering the designs of actual Miller engines.
5
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Effects of Equivalence Ratio and Mean Piston Speed on Performance of an Irreversible Dual Cycle

80%
Ebrahimi R.
Acta Physica Polonica A
|
2011
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vol. 120
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issue 3
384-389
EN
In the present study, the performance of an air standard dual cycle is analyzed using finite-time thermodynamics. The relations between the power output and the compression ratio, between the power output and the thermal efficiency are derived by detailed numerical examples. The results show that the maximum power output and the power output at the maximum efficiency point increase and then decrease as the equivalence ratio and/or the mean piston speed increases. The results also show that the optimal compression ratio corresponding to maximum power output point and the working range of the cycle remain constant as the mean engine speed is increased, but they increase and then decrease as the equivalence ratio is increased. It is noteworthy that the results obtained in the present study are of significance for providing guidance with respect to the performance evaluation of practical internal combustion engines.
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Phase Field Modeling of the Zn_{1-x}Cd_xO Solid Solutions

80%
Shtepliuk I., Podolskaia N., Lashkarev G.
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vol. 126
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issue 5
1079-1082
EN
The analysis of spinodal decomposition in the Zn_{1-x}Cd_xO ternary alloy was carried out by means of the nonlinear Cahn-Hilliard equation. Interaction parameter as a function of composition x was provided by valence force field simulations and was used in this analysis. The morphological patterns for the ternary alloys with different Cd content (x=5, 10, 50%) were experimentally obtained using the semi-implicit Fourier-spectral method. The simulated microstructure evolution Zn_{0.95}Cd_{0.05}O demonstrates that the microstructure having a form of bicontinuous worm-like network is evolved with the progress of aging. An effect of the phase-field mobility and the gradient energy on the microstructure evolution of the Zn_{1-x}Cd_xO alloys is discussed. It was found that the higher driving force for the decomposition in the higher Cd content film results in a higher decomposition rate revealed by the simulations. The temporal evolution of the simulated Zn_{0.95}Cd_{0.05}O microstructure is in good agreement with experimental results, which have been obtained for this solid solution.
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Performance Prediction and Irreversibility Analysis of a Thermoelectric Refrigerator with Finned Heat Exchanger

80%
Meng F., Chen L., Sun F.
Acta Physica Polonica A
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2011
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vol. 120
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issue 3
397-406
EN
A developed model of commercial thermoelectric refrigerators with finned heat exchanger is established by introducing finite time thermodynamics. A significant novelty is that physical properties, dimension parameters, temperature parameters and flow parameters are all taken into account in the model. Numerical studies and comparative investigation on the performance of a typical commercial water-cooling thermoelectric refrigerator which consists of 127 thermoelectric elements, are performed for cooling load and coefficient of performance. The results show that the maximum cooling load is 2.33 W and the maximum coefficient of performance is 0.54 when the cooling temperature difference is 10 K. Comparing the simulation results of several models, it is found that the heat convection of the heat exchanger and the heat leakage through the air gap are the main factors, which cause irreversibility and decrease the performance. Moreover, the performance can be improved by optimizing the length and cross-section area of thermoelectric elements. The model and calculation method may be applied to not only the analysis and performance prediction of practical thermoelectric refrigerators, but also the design and optimization of heat exchangers.
8
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Thermodynamic Modeling of an Atkinson Cycle with respect to Relative Air-Fuel Ratio, Fuel Mass Flow Rate and Residual Gases

80%
Ebrahimi R.
Acta Physica Polonica A
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2013
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vol. 124
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issue 1
29-34
EN
The performance of an air standard Atkinson cycle is analyzed using finite-time thermodynamics. The results show that if the compression ratio is less than a certain value, the power output increases with increasing relative air-fuel ratio, while if the compression ratio exceeds a certain value, the power output first increases and then starts to decrease with increase of relative air-fuel ratio. With a further increase in compression ratio, the increase in relative air-fuel ratio results in decrease of the power output. Throughout the compression ratio range, the power output increases with increase of fuel mass flow rate. The results also show that if the compression ratio is less than a certain value, the power output increases with increase of residual gases, on the contrast, if the compression ratio exceeds a certain value, the power output decreases with increase of residual gases. The results obtained herein can provide guidance for the design of practical Atkinson engines.
9
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Endoreversible Modeling and Optimization of a Multistage Heat Engine System with a Generalized Heat Transfer Law via Hamilton-Jacobi-Bellman Equations and Dynamic Programming

80%
Xia S., Chen L., Sun F.
Acta Physica Polonica A
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2011
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vol. 119
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issue 6
747-760
EN
A multistage endoreversible Carnot heat engine system operating between a finite thermal capacity high-temperature fluid reservoir and an infinite thermal capacity low-temperature environment with a generalized heat transfer law [q ∝ ( Δ (T^{n}))^{m}] is investigated in this paper. Optimal control theory is applied to derive the continuous Hamilton-Jacobi-Bellman equations, which determine the optimal fluid temperature configurations for maximum power output under the conditions of fixed initial time and fixed initial temperature of the driving fluid. Based on the general optimization results, the analytical solution for the case with Newtonian heat transfer law [q ∝ Δ(T)] is further obtained. Since there are no analytical solutions for the other heat transfer laws, the continuous Hamilton-Jacobi-Bellman equations are discretized and the dynamic programming algorithm is adopted to obtain the complete numerical solutions of the optimization problem, and the relationships among the maximum power output of the system, the process period and the fluid temperature are discussed in detail. The results show that the optimal high-temperature fluid reservoir temperature for the maximum power output of the multistage heat engine system with Newtonian and linear phenomenological [q ∝ Δ (T^{-1})] heat transfer laws decrease exponentially and linearly with time, respectively, while those with the Dulong-Petit [q∝(Δ T)^{1.25}], radiative [q∝ Δ (T^4)] and [q∝(Δ(T^4))^{1.25}] heat transfer laws are different from the former two cases significantly.
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The Effects of Cycle Temperature and Cycle Pressure Ratios on the Performance of an Irreversible Otto Cycle

80%
Ust Y., Sahin B., Safa A.
Acta Physica Polonica A
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2011
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vol. 120
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issue 3
412-416
EN
This paper reports the thermodynamic optimization based on the maximum mean effective pressure, maximum power and maximum thermal efficiency criteria for an irreversible Otto heat engine model which includes internal irreversibility resulting from the adiabatic processes. The mean effective pressure, power output, and thermal efficiency are obtained by introducing the compression ratio, cycle temperature ratio, specific heat ratio and the compression and expansion efficiencies. Optimal performance and design parameters of the Otto cycle are obtained analytically for the maximum power and maximum thermal efficiency conditions and numerically for the maximum mean effective pressure conditions. The results at maximum mean effective pressure conditions are compared with those results obtained by using the maximum power and maximum thermal efficiency criteria. The effects of the cycle temperature ratio and cycle pressure ratio on the general and optimal performances are investigated.
11
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Analysis of Irreversible Processes across Narrow Junctions

80%
Honig J., Hoehn R.
Acta Physica Polonica A
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2011
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vol. 119
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issue 3
323-327
EN
The rectification of the second law of thermodynamics is used to directly relate irreversible heat and work transfers to reversible processes. This permits the construction of thermodynamic functions of state that include entropy contributions due to irreversible processes. A general expression is set up to determine the entropy changes in terms of experimentally accessible parameters when a system is interacting with its surroundings via quasistatic irreversible operations. The procedure is used to determine the entropy changes across a narrow junction in terms of pressure and temperature differences between the system and its surroundings, including cyclic processes.
12
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Effects of Variable Specific Heat Ratio on Performance οf an Endoreversible Otto Cycle

80%
Ebrahimi R.
|
|
issue 6
887-891
EN
Using finite-time thermodynamics, the relations between the work output and the compression ratio, between the thermal efficiency and the compression ratio for an endoreversible Otto cycle are derived with variable specific heat ratio of working fluid. The results show that if compression ratio is less than certain value, the increase of specific heat ratio makes the work output and the thermal efficiency higher; on the contrary, if compression ratio exceeds certain value, the increase of specific heat ratio makes the work output and the thermal efficiency less. The results also show that the maximum work output, the compression ratio at the maximum work output point, the working range of the cycle and the compression ratio at maximum thermal efficiency point decrease as the specific heat ratio increased. The results obtained from this work can be helpful in the thermodynamic modeling and in the evaluation of real Otto engines.
13
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Performance Analysis of a Diesel Cycle under the Restriction of Maximum Cycle Temperature with Considerations of Heat Loss, Friction, and Variable Specific Heats

80%
Hou S., Lin J.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6
979-986
EN
The objective of this study is to examine the influences of heat loss characterized by a percentage of fuel's energy, friction and variable specific heats of working fluid on the performance of an air standard Diesel cycle with the restriction of maximum cycle temperature. A more realistic and precise relationship between the fuel's chemical energy and the heat leakage that is constituted on a pair of inequalities is derived through the resulting temperature. The variations in power output and thermal efficiency with compression ratio, and the relations between the power output and the thermal efficiency of the cycle are presented. The results show that the power output as well as the efficiency where maximum power output occurs will increase with the increase of maximum cycle temperature. The temperature-dependent specific heats of working fluid have a significant influence on the performance. The power output and the working range of the cycle increase while the efficiency decreases with increasing specific heats of working fluid. The friction loss has a negative effect on the performance. Therefore, the power output and efficiency of the cycle decrease with increasing friction loss. It is noteworthy that the effects of heat loss characterized by a percentage of fuel's energy, friction and variable specific heats of working fluid on the performance of a Diesel-cycle engine are significant and should be considered in practice cycle analysis. The results obtained in the present study are of importance to provide a good guidance for the performance evaluation and improvement of practical Diesel engines.
14
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Performance Analysis of a Dual Cycle Engine with Considerations of Pressure Ratio and Cut-Off Ratio

80%
Ebrahimi R.
|
|
issue 4
534-539
EN
The dual cycle is a better approximation to the modern high speed compression ignition engine than either the Diesel cycle or the Otto cycle. Therefore, this study is aimed at investigating the effects of pressure and cut-off ratios on the dual cycle performance with considerations of heat transfer loss, variable specific heat ratio and friction irreversible losses. By using finite-time thermodynamics theory, the relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between power output and the efficiency of the cycle are obtained. The results show that if compression ratio is smaller than certain value, the increase of pressure ratio and the decrease of cut-off ratio make the power output bigger. While if compression ratio exceeds certain value, the power output first increases and then starts to decline as pressure ratio and cut-off ratio are increased. With further increase in compression ratio, the power output decreases with increasing pressure ratio and decreasing cut-off ratio. The effects of pressure and cut-off ratios on the variation of the thermal efficiency with compression ratio are similar to those for the power output. The results obtained in this work can provide significant guidance for the performance evaluation and improvement of modern high speed compression ignition engines.
15
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Effect of Expansion-Compression Ratio on Performance of the Miller cycle

80%
Ebrahimi R.
Acta Physica Polonica A
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2012
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vol. 122
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issue 4
645-649
EN
The objective of this study is to analyze the effect of expansion-compression ratio on the performance of dual cycle. Using finite-time thermodynamics, the relations between thermal efficiency, power output and compression ratio for an air standard Miller cycle have been derived. In the model, the nonlinear relation between the specific heats of working fluid and its temperature, the frictional loss computed according to the mean velocity of the piston, and heat transfer loss are considered. The results show that the power output first increases with the increasing expansion-compression ratio and then starts to decrease. Comparisons of the power output of the Miller, Otto, and Atkinson cycles show that if compression ratio is less than certain value, the power output for Otto cycle is higher, while if compression ratio exceeds certain value, the power output for the Miller cycle is higher. With further increase in compression ratio, the power output for Atkinson cycle is higher. In high compression ratio, the power output of the Miller cycle is higher. The results obtained in the present study provide guidance to the performance evaluation and improvement for practical internal combustion engines.
16
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Second Law Analysis on an Air-Standard Miller Engine

80%
Ebrahimi R.
Acta Physica Polonica A
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2016
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vol. 129
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issue 6
1079-1082
EN
Performance analysis has been carried out for air-standard Miller engine using second law analysis. The relations of the second law efficiency versus compression ratio, the second law efficiency versus first law efficiency as well as the exergy versus compression ratio are obtained. The results show that the curve of second law efficiency versus first law efficiency is a parabolic-like one. The results also show that, throughout the compression ratio range, the second law efficiency increases when the expansion-compression ratio increases.
17
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Anisotropic Phase Field Model of Heteroepitaxial Growth

80%
Hoang D., Beneš M., Stráský J.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
520-522
EN
We study the heteroepitaxial growth of thin layers by means of the modified phase-field model with the incorporated anisotropy. The influence of elastic and surface energies on the layer growth is considered. For numerical solution of the model, an explicit numerical scheme based on the finite element method is employed. The obtained computational results with various anisotropy settings demonstrate the anisotropic thin-layer pattern growth.
18
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Local Real Estate Markets in Poland as a Network of Damped Harmonic Oscillators

80%
Kulesza S., Belej M.
Acta Physica Polonica A
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2015
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vol. 127
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issue 3A
A-99-A-102
EN
The paper deals with time series of housing prices on local real estate markets in Warszawa (WAW), Kraków (KRK) and Poznań (POZ) from 2006 to 2013 using a model of critically-damped harmonic oscillator to study underlying system dynamics. Performed analysis reveals the presence of housing bubble in 2007 that emerge from otherwise quasi-regular evolution around the equilibrium state. Time series of housing prices are fitted numerically to estimate important parameters of the system, for example: decay constant, delay time, and price equilibrium level, which help us to chose the leading market. Obtained results show reasonable matching of the model with housing prices in WAW and POZ, but less in KRK. The latter data, however, are found to agree well with the model of under-damped harmonic oscillator, which actually suggests that some trembling might occur in that market. Nevertheless, local real estate markets can be thought of as a system of interconnected damped harmonic oscillators with leading market in WAW that is about to change under aggregate macroeconomic fluctuations (exogenous factors) triggering changes in remaining markets.
19
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Evaporation of Micro-Droplets: the "Radius-Square-Law" Revisited

70%
Jakubczyk D., Kolwas M., Derkachov G., Kolwas K., Zientara M.
Acta Physica Polonica A
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2012
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vol. 122
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issue 4
709-716
EN
The range of applicability of a fundamental tool for studying the evolution of droplets, the "radius-square-law", was investigated both analytically and numerically, on the basis of the experimental results of our own as well as of other authors. Standard issues were briefly discussed. Departures from the "radius-square-law" caused by the influence of impurities encountered in non-ideal liquids, by the kinetic and surface tension effects encountered for small droplets or by thermal imbalance encountered in light-absorbing droplets were analysed. The entanglement between the kinetic and impurities effects was studied numerically yielding a possible explanation to evaporation coefficient discrepancies found in the literature. An unexpected "radius-square-law" persistence in case of non-isothermal evolutions of very small droplets in atmosphere nearly saturated with vapour was analysed. The coexistence of the kinetic effects and the strong effects of surface tension was found responsible for this effect.
20
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Lévy-statistics for partially equilibrated systems

70%
Petridis A.
Open Physics
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2006
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vol. 4
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issue 3
363-368
EN
We examine deviations from Boltzmann-Gibbs statistics for a certain class of partially equilibrated systems of finite size. We find that such systems are characterized by the Lévy distribution whose non-extensivity parameter is related to the number of internally equilibrated subsystems and to correlations among them. This concept is applicable to relativistic heavy ion collisions.
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