Irreversible Entropy Generation Research Articles

A two-scale thermodynamic entropy model for rapid high-cycle fatigue property evaluation of welded joints

This investigation attempts to propose a two-scale thermodynamic entropy model that can quantify the micro-scale fatigue behaviors from the macroscopic level. Both non-damaging anelastic and damaging inelastic microstructural motions that cause entropy generation at different stress amplitude blocks of specimens are considered. On this basis, a thermodynamically based correlation between the macro-stress amplitude and the microstructural motion is constructed following the framework of thermodynamics. Butt joints made of low carbon steel are used as the experimental materials in this work. The fatigue limit of welded joints is estimated in a short time using the developed approach in combination with the correlation coefficient optimization method. Finally, the fracture fatigue entropy (FFE) model, corresponding to the two-scale theory, is developed to achieve fast prediction of fatigue life by considering the threshold value associated with the irreversible inelastic entropy generation in high-cycle fatigue. The results show that the predicted data are in satisfactory agreement with the experimental data.

Irreversibility analysis for flow of carbon nanotubes with varying length and radius: Applications in rocket engine

In this research work, the two-dimensional (2D), incompressible fluid flow has been taken into consideration. The flow is supposed to be steady and laminar. By considering the water-based nanoparticles of SWCNTs and MWCNTs in the presence of thermal radiation, the rate of heat transferring and entropy generation effects in a regenerative cooling system of a rocket engine are evaluated. The effects of the length and radius of the nanomaterials on the problem are also considered. Solutions for temperature, velocity profile, irreversibility (entropy generation) and the Bejan number are discussed graphically, and the effects of various significant factors are considered on these profiles. The modeled physical problems in current exploration are dependent upon governing laws which appear in terms of PDEs. These PDEs are reformed into a system of nonlinear ODEs. We used numerical scheme known as (RK-4) in combination with the shooting iteration technique to obtain the solutions to transformed fluid flow equations, because the resultant ODEs are extremely nonlinear and finding the exact solution is very difficult. It is investigated that the Eckert number, nanoparticles volume fraction and radiation parameter upsurge the thermal field as well as the irreversibility of the system. Furthermore, the dual behavior of nanoparticles volume fraction and viscosity parameter on velocity profile is observed. Bejan number shows increasing effects in response to nanoparticles volume fraction and radiation parameter, whereas a reverse impact of Bejan number is noticed for the rising values of Eckert number.

Entropy Flow Analysis of Thermal Transmission Process in Integrated Energy System Part II: Comparative Case Study

The dynamic characteristics of thermal energy play an important role of multi-scale coupling among heterogeneous energy sources in integrated energy systems (IES). In Part I, for the purpose of accurately describing the dynamic processes of thermal energy transmission, the theoretical approach and models were proposed and verified by numerical simulation. In this part, an innovative analytical method based on entropy flow was derived on the basis of theory developed in Part I, which can assess the quantity and quality of thermal transport. A comparative case study indicates that the change trend of entropy flow of each node is consistent with the change of available power, but independent of temperature. The node entropy flow is increased compared with the algebraic sum of branch entropy flow, which reflects the phenomenon of entropy generation in the mixing process; while the change of available power is just the opposite. This means the irreversible entropy generation at the node leads to loss of the available thermal power. Therefore, it is more accurate to describe the dynamic thermal transmission process on the scale of entropy. This proves the effectiveness of the models proposed in Part I as well as the methods in this part from the perspective of application.

A Port Hamiltonian approach to dynamical chemical process systems network modeling and analysis

This work focuses on the investigation of the applicability of port Hamiltonian systems (PHS) approach to model chemical process plant systems and the generalization of the PHS originally proposed for reversible thermodynamic systems to irreversible thermodynamic system characterized by coupled physicochemical phenomenon and significant irreversible entropy generation. To this end, the first part of this work presents a definition and analysis of the proposed generalized class of conservative pseudo port Hamiltonian system for general open multi-input multi-output (MIMO) irreversible thermodynamic system. In the second part of the work, the generalized PHS approach is applied to multiphase process systems with coupled irreversible entropy generation. The proposed modeling framework is extended to model chemical process systems network with recycle, which is prevalent in chemical process plants.

Battery absorbs heat during charging uncovered by ultra-sensitive thermometry

The reversible heat in lithium-ion batteries (LIBs) due to entropy change is fundamentally important for understanding the chemical reactions in LIBs and developing proper thermal management strategies. However, the direct measurements of reversible heat are challenging due to the limited temperature resolution of applied thermometry. In this work, by developing an ultra-sensitive thermometry with a differential AC bridge using two thermistors, the noise-equivalent temperature resolution we achieve (±10 μK) is several orders of magnitude higher than previous thermometry applied on LIBs. We directly observe reversible heat absorption of a LIR2032 coin cell during charging with negligible irreversible heat generation and a linear relation between heat generations and currents. The cell entropy changes determined from the reversible heat provide the first verification of the approach of temperature dependent open circuit voltage. Moreover, it is found that the large reversible entropy change can cancel out the irreversible entropy generation at a charging rate as large as C/3.7 and produce a zero-heat-dissipation battery during charging. Our work significantly contributes to fundamental understanding of the entropy changes and heat generations of the chemical reactions in LIBs, and reveals that reversible heat absorption can be an effective way to cool LIBs during charging. Ultra-sensitive thermometry with temperature resolution of 10 μK reveals that batteries absorb heat reversibly during charging. • An ultra-sensitive thermometry with a noise-equivalent resolution of 10 μK. • Observing reversible heat of batteries with negligible irreversible heat generation. • Entropy changes from reversible heat match with that from open circuit voltage. • Batteries generate zero heat with a charging rate of C/3.7

Consistency of optimizing finite-time Carnot engines with the low-dissipation model in the two-level atomic heat engine

The efficiency at the maximum power (EMP) for finite-time Carnot engines established with the low-dissipation model, relies significantly on the assumption of the inverse proportion scaling of the irreversible entropy generation ΔS (ir) on the operation time τ, i.e. ΔS (ir) ∝ 1/τ. The optimal operation time of the finite-time isothermal process for EMP has to be within the valid regime of the inverse proportion scaling. Yet, such consistency was not tested due to the unknown coefficient of the 1/τ-scaling. In this paper, we reveal that the optimization of the finite-time two-level atomic Carnot engines with the low-dissipation model is consistent only in the regime of η C ≪ 2(1 − δ)/(1 + δ), where η C is the Carnot efficiency, and δ is the compression ratio in energy level difference of the heat engine cycle. In the large-η C regime, the operation time for EMP obtained with the low-dissipation model is not within the valid regime of the 1/τ-scaling, and the exact EMP of the engine is found to surpass the well-known bound η + = η C/(2 − η C).

Entropy analysis for second grade nanomaterials flow with thermophoresis and Brownian diffusions

Numerical approach is implemented for irreversibility analysis of second grade nanomaterials flow with slip and Lorentz force effects. Joule heating and radiation effects are present in heat expression. Thermophoresis and random motion characteristics are incorporated. Entropy analysis is studied through thermodynamics second law. The governing partial systems are transmitted into ordinary systems by appropriate variables. The resultant ordinary systems are solved through numerical scheme (Newton built in-shooting method). Here our main theme is to address heat transportation and irreversibility (entropy generation) analyses. Graphical illustrations analyze the variation in flow, entropy rate, thermal field and concentration descriptions influenced by important dimensionless variables. An increment in velocity field is noticed versus magnetic variable. An amplification in curvature variable improves thermal field and velocity. An intensification in radiation effect corresponds to augments the entropy and thermal distribution. An opposite trend holds for thermal and concentration distributions through random motion variable. A reduction occurs in entropy analysis with variation in slip variable.

Impact of irreversibility ratio and entropy generation on three-dimensional Oldroyd-B fluid flow with relaxation–retardation viscous dissipation

The study is concerned with entropy minimization on three-dimensional magnetohydrodynamic Oldroyd-B fluid flow with relaxation–retardation viscous dissipation and a mixed chemical reaction. A numerical solution of the nonlinear transport equations is obtained using an overlapping grid spectral collocation numerical scheme. We investigate strategies for entropy generation minimization in terms of system parameters such as the mixed convection parameter and changes in thermal and concentration fields under different conditions. Further, the findings on changes in the axial and transverse skin friction coefficients, the Nusselt number and the Sherwood number are presented.

Experimental Test of the 1/τ-Scaling Entropy Generation in Finite-Time Thermodynamics.

The finite-time dynamics, apart from its fundamental importance in nonequilibrium thermodynamics, is of great significance in designing heat engine cycles. We build an experimental apparatus to test the predicted long-time 1/τ scaling of the irreversible entropy generation in the finite-time (τ) thermodynamic process by compressing dry air in a temperature-controlled water bath. We present the first direct experimental validation of the scaling, utilized in many finite-time thermodynamic models at the long-time regime. The experimental data also demonstrate a clear deviation from the scaling at the short-time regime. We show the optimal control scheme to minimize the irreversible entropy generation in finite-time process. Such optimization shall bring new insight to the practical design of heat engine cycles.

Entropy Generation Methodology for Defect Analysis of Electronic and Mechanical Components—A Review

Understanding the defect characterization of electronic and mechanical components is a crucial step in diagnosing component lifetime. Technologies for determining reliability, such as thermal modeling, cohesion modeling, statistical distribution, and entropy generation analysis, have been developed widely. Defect analysis based on the irreversibility entropy generation methodology is favorable for electronic and mechanical components because the second law of thermodynamics plays a unique role in the analysis of various damage assessment problems encountered in the engineering field. In recent years, numerical and theoretical studies involving entropy generation methodologies have been carried out to predict and diagnose the lifetime of electronic and mechanical components. This work aimed to review previous defect analysis studies that used entropy generation methodologies for electronic and mechanical components. The methodologies are classified into two categories, namely, damage analysis for electronic devices and defect diagnosis for mechanical components. Entropy generation formulations are also divided into two detailed derivations and are summarized and discussed by combining their applications. This work is expected to clarify the relationship among entropy generation methodologies, and benefit the research and development of reliable engineering components.

RETRACTED: Free convection and entropy generation in a nanofluid-filled star-ellipse annulus using lattice Boltzmann method supported by immersed boundary method

Abstract In the present work, it is aimed to investigate the natural convection numerically. The nanofluid flow and heat transfer in a star-ellipse annulus are investigated. The lattice Boltzmann method is utilized to carry out the numerical simulations. In addition, the Immersed Boundary Method (IBM) is used to treat the Dirichlet and Neumann conditions. The annulus consists a star-shaped cylinder and ellipse cylinder and filled with Cu-water nanofluid. The second law analysis is used to provide local maps of fluid friction irreversibility and heat transfer irreversibility and volumetric entropy generation. The influences of some main parameters including Rayleigh number in a range of 103 to 106, solid volume fraction of nanofluid in range of 0 to 0.03 and eccentricity -0.4

Entropy analysis in moving wavy surface boundary-layer

It is a well-established fact that significant gain in the heat transfer rate can be obtained by altering that flat surface texture of the working body. The most convenient alteration, in view of mathematical handling, is the wavy one. Existing studies reveal that the convective heat transfer phenomenon is affected significantly due to the presence of a solid wavy surface. How does the phenomena of entropy generation is effected due to a wavy surface is the question investigated in this manuscript. The expressions for irreversibility distribution rate, Bejan number, and volumetric entropy generation number have been evaluated by Keller-Box method. The effect of important parameters of interest, such as wavy amplitude, Prandtl number, and group parameter on irreversibility distribution rate, Bejan number and entropy generation number, have been discussed in detail. The study reveals that entropy generation number decreases and irreversibility rate increases by increasing the amplitude of the wavy surface.

Optimal operating protocol to achieve efficiency at maximum power of heat engines.

Efficiency at maximum power has been investigated extensively, yet the practical control scheme to achieve it remains elusive. We fill this gap with a stepwise Carnot-like cycle, which consists of the discrete isothermal process (DIP) and adiabatic process. With DIP, we validate the widely adopted assumption of the C/t relation of the irreversible entropy generation S^{(ir)} and show the explicit dependence of the coefficient C on the fluctuation of the speed of tuning energy levels as well as the microscopic coupling constants to the heat baths. Such a dependence allows us to control the irreversible entropy generation by choosing specific control schemes. We further demonstrate the achievable efficiency at maximum power and the corresponding control scheme with the simple two-level system. Our current work opens new avenues for an experimental test, which was not feasible due to the lack the of the practical control scheme in the previous low-dissipation model or its equivalents.

Entropy generation for flow of Sisko fluid due to rotating disk

This investigation deals with entropy generation optimization and nonlinear dissipative flow of Sisko fluid due to a rotating disk. Joule heating effect is considered. Mathematical model is obtained for the present flow problem. Nonlinear systems are solved for convergent series solutions. Analysis of various flow variables on Bejan number, volumetric entropy generation rate, temperature and velocity are discussed. Present analysis depicts that irreversibility rate (entropy generation rate) and Bejan number are enhanced for radiation parameter, whereas reverse behavior is noticed for Brinkman number and material parameter. The velocity and temperature fields are increasing for larger material parameter and temperature ratio parameter. The obtained results are helpful in understanding the irreversibility (entropy generation) for flow of non-Newtonian fluids. Comparative study is made for temperature, velocity, Bejan number and entropy generation by considering shear thickening and thinning fluids. Finally, a comparison is given with the previous available results.

Determination of LEDs degradation with entropy generation rate

We propose a method to assess the degradation and aging of light emitting diodes (LEDs) based on irreversible entropy generation rate. We degraded several LEDs and monitored their entropy generation rate (Ṡ) in accelerated tests. We compared the thermoelectrical results with the optical light emission evolution during degradation. We find a good relationship between aging and Ṡ (t), because Ṡ is both related to device parameters and optical performance. We propose a threshold of Ṡ (t) as a reliable damage indicator of LED end-of-life that can avoid the need to perform optical measurements to assess optical aging. The method lays beyond the typical statistical laws for lifetime prediction provided by manufacturers. We tested different LED colors and electrical stresses to validate the electrical LED model and we analyzed the degradation mechanisms of the devices.

Numerical studies for performance improvement of a variable geometry dual mode combustor by optimizing deflection angle

As part of our efforts to study the effect of the deflection angle on combustor performance of a variable geometry dual mode combustor, the flow field characteristics and mechanisms of the combustor performance loss, which comprised of compression loss, combustion heat addition loss and expansion loss, were investigated in the variable geometry dual mode combustor numerically with a Mach number of 3, a divergence ratio of 1.76, a fuel equivalence ratio of 0.6, and a deflection angle ranging from 8° to 16°. Numerical results indicated that the total pressure recovery coefficient and combustion efficiency increased with the deflection angle and there was a maximum to be obtained at the deflection angle of 12° due to the interaction between the dominant shock resulted by combustion heat release and the additional shock caused by the wedge system. Irreversible entropy generation loss was analyzed specifically in this paper to clarify and describe the combustor performance loss for the variable geometry dual mode combustor. Moreover, thrust-to-drag ratio was utilized to assess the effect of the deflection angle on combustor performance. By taking into account the flow field characteristics and combustor performance characteristics, the high combustor performance of a variable geometry dual mode combustor can be improved by selecting and optimizing the deflection angle.

Entropy characterisation of overstressed capacitors for lifetime prediction

Abstract We propose a method to monitor the ageing and damage of capacitors based on their irreversible entropy generation rate. We overstressed several electrolytic capacitors in the range of 33 μF–100 μF and monitored their entropy generation rate S ˙ (t). We found a strong relationship between capacitor degradation and S ˙ (t). Therefore, we proposed a threshold for S ˙ (t) as an indicator of capacitor time-to-failure. This magnitude is related to both capacitor parameters and to a damage indicator such as entropy. Our method goes beyond the typical statistical laws for lifetime prediction provided by manufacturers. We validated the model as a function of capacitance, geometry, and rated voltage. Moreover, we identified different failure modes, such as heating, electrolyte dry-up and gasification from the dependence of S ˙ (T) with temperature, T. Our method was implemented in cheap electrolytic capacitors but can be easily applied to any type of capacitor, supercapacitor, battery, or fuel cell.

The effects of moist entropy and moisture budgets on tropical cyclone development

AbstractThis paper examines the moist entropy and moisture budgets in tropical cyclones, as well as their relation to tropical cyclone's development. This analysis focuses on the dropsonde data collected during Hurricane and Severe Storm Sentinel project and the accompanying satellite data. Two tropical cyclones of interest are Tropical Storm Gabrielle (2013) and Hurricane Edouard (2014). There were three research flights into Gabrielle (2013), during its nondeveloping and decaying stages. Edouard (2014) was visited four times in different stages of its life cycle, twice during the intensification and twice during the decay. Also, we extended our analysis on the larger data set, consisting of 11 nonintensifying and 12 intensifying systems. Our study shows that the moist entropy tends to increase during intensification and decrease during nonintensifying stages. On the other hand, the moisture budget relates better to the tropical cyclone's current intensity than its development. The sign of the moist entropy tendency depends on the ability of surface fluxes and irreversible moist entropy generation to overcome lateral export of moist entropy and loss due to radiative cooling. Edouard's decay during the last research flight was likely the result of increasing wind shear and low sea surface temperatures. During its decay, Gabrielle had strong column‐integrated lateral export of moist entropy and drying between 1 and 4 km height. This is probably the consequence of a dry environment at multiple levels, amplified by a warm and dry anomaly left behind by previous convective activity.

From steam engine to solar cells: can thermodynamics guide the development of future generations of photovoltaics?

Thermodynamics has played a singular role in the development of virtually all energy technologies to‐date. This review argues that it also has a role to play in the understanding and design of solar cell operation, particularly looking toward the future, high‐efficiency solar cells. After a historical overview of the key developments in the ‘thermodynamics of light,’ the conversion of a monochromatic light beam is used as a starting point to analyze the conversion process, examine the fundamental losses in terms of irreversible entropy generation, and consider in detail one of the key applications: the Shockley–Queisser detailed balance. We review and compare the principal suggestions for the highest theoretical efficiency of solar energy conversion, and analyze one possible embodiment of such a third‐generation structure: the hot‐carrier solar cell. A somewhat different application of the statistical approach—light trapping—is reviewed at a fundamental level, and the future potential is considered for devices which combine such a ‘thermodynamic squeezing’ of light with latest developments in photonics, leading to a photonic bandgap solar cell. We argue that the widespread use of thermodynamic tools in the current photovoltaics research, especially when combined with the potential benefits to future devices, already indicates that our thinking should not be about if but how thermodynamics can guide us to make better solar cells. WIREs Energy Environ 2016, 5:543–569. doi: 10.1002/wene.204This article is categorized under: Photovoltaics > Science and Materials Solar Heating and Cooling > Science and Materials

Irreversible entropy model for damage diagnosis in resistors

We propose a method to characterize electrical resistor damage based on entropy measurements. Irreversible entropy and the rate at which it is generated are more convenient parameters than resistance for describing damage because they are essentially positive in virtue of the second law of thermodynamics, whereas resistance may increase or decrease depending on the degradation mechanism. Commercial resistors were tested in order to characterize the damage induced by power surges. Resistors were biased with constant and pulsed voltage signals, leading to power dissipation in the range of 4–8 W, which is well above the 0.25 W nominal power to initiate failure. Entropy was inferred from the added power and temperature evolution. A model is proposed to understand the relationship among resistance, entropy, and damage. The power surge dissipates into heat (Joule effect) and damages the resistor. The results show a correlation between entropy generation rate and resistor failure. We conclude that damage can be conveniently assessed from irreversible entropy generation. Our results for resistors can be easily extrapolated to other systems or machines that can be modeled based on their resistance.