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2601 KiB

Open AccessArticle

2D Temperature Analysis of Energy and Exergy Characteristics of Laminar Steady Flow across a Square Cylinder under Strong Blockage

by M. Ozgun Korukcu

Entropy 2015, 17(5), 3124-3151; https://doi.org/10.3390/e17053124 - 12 May 2015

Cited by 2 | Viewed by 5356

Abstract

Energy and exergy characteristics of a square cylinder (SC) in confined flow are investigated computationally by numerically handling the steady-state continuity, Navier-Stokes and energy equations in the Reynolds number range of Re = 10–50, where the blockage ratio (β = B/H) is kept [...] Read more.

Energy and exergy characteristics of a square cylinder (SC) in confined flow are investigated computationally by numerically handling the steady-state continuity, Navier-Stokes and energy equations in the Reynolds number range of Re = 10–50, where the blockage ratio (β = B/H) is kept constant at the high level of β = 0.8. Computations indicated for the upstream region that, the mean non-dimensional streamwise (u/U_o) and spanwise (v/U_o) velocities attain the values of u/U_o = 0.840®0.879 and v/U_o = 0.236®0.386 (Re = 10®50) on the front-surface of the SC, implying that Reynolds number and blockage have stronger impact on the spanwise momentum activity. It is determined that flows with high Reynolds number interact with the front-surface of the SC developing thinner thermal boundary layers and greater temperature gradients, which promotes the thermal entropy generation values as well. The strict guidance of the throat, not only resulted in the fully developed flow character, but also imposed additional cooling; such that the analysis pointed out the drop of duct wall (y = 0.025 m) non-dimensional temperature values (ζ) from ζ = 0.387®0.926 (Re = 10®50) at x_th = 0 mm to ζ = 0.002®0.266 at x_th = 40 mm. In the downstream region, spanwise thermal disturbances are evaluated to be most inspectable in the vortex driven region, where the temperature values show decrease trends in the spanwise direction. In the corresponding domain, exergy destruction is determined to grow with Reynolds number and decrease in the streamwise direction (x_ds = 0®10 mm). Besides, asymmetric entropy distributions as well were recorded due to the comprehensive mixing caused by the vortex system. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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766 KiB

Open AccessArticle

Exergy Analysis of a Ground-Coupled Heat Pump Heating System with Different Terminals

by Xiao Chen and Xiaoli Hao

Entropy 2015, 17(4), 2328-2340; https://doi.org/10.3390/e17042328 - 17 Apr 2015

Cited by 10 | Viewed by 8132

Abstract

In order to evaluate and improve the performance of a ground-coupled heat pump (GCHP) heating system with radiant floors as terminals, an exergy analysis based on test results is performed in this study. The system is divided into four subsystems, and the exergy [...] Read more.

In order to evaluate and improve the performance of a ground-coupled heat pump (GCHP) heating system with radiant floors as terminals, an exergy analysis based on test results is performed in this study. The system is divided into four subsystems, and the exergy loss and exergy efficiency of each subsystem are calculated using the expressions derived based on exergy balance equations. The average values of the measured parameters are used for the exergy analysis. The analysis results show that the two largest exergy losses occur in the heat pump and terminals, with losses of 55.3% and 22.06%, respectively, and the lowest exergy efficiency occurs in the ground heat exchange system. Therefore, GCHP system designers should pay close attention to the selection of heat pumps and terminals, especially in the design of ground heat exchange systems. Compared with the scenario system in which fan coil units (FCUs) are substituted for the radiant floors, the adoption of radiant floors can result in a decrease of 12% in heating load, an increase of 3.24% in exergy efficiency of terminals and an increase of 1.18% in total exergy efficiency of the system. The results may point out the direction and ways of optimizing GCHP systems. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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1227 KiB

Open AccessArticle

Experimental and Thermoeconomic Analysis of Small-Scale Solar Organic Rankine Cycle (SORC) System

by Suresh Baral, Dokyun Kim, Eunkoo Yun and Kyung Chun Kim

Entropy 2015, 17(4), 2039-2061; https://doi.org/10.3390/e17042039 - 7 Apr 2015

Cited by 72 | Viewed by 10638

Abstract

A small-scale solar organic Rankine cycle (ORC) is a promising renewable energy-driven power generation technology that can be used in the rural areas of developing countries. A prototype was developed and tested for its performance characteristics under a range of solar source temperatures. [...] Read more.

A small-scale solar organic Rankine cycle (ORC) is a promising renewable energy-driven power generation technology that can be used in the rural areas of developing countries. A prototype was developed and tested for its performance characteristics under a range of solar source temperatures. The solar ORC system power output was calculated based on the thermal and solar collector efficiency. The maximum solar power output was observed in April. The solar ORC unit power output ranged from 0.4 kW to 1.38 kW during the year. The highest power output was obtained when the expander inlet pressure was 13 bar and the solar source temperature was 120 °C. The area of the collector for the investigation was calculated based on the meteorological conditions of Busan City (South Korea). In the second part, economic and thermoeconomic analyses were carried out to determine the cost of energy per kWh from the solar ORC. The selling price of electricity generation was found to be $0.68/kWh and $0.39/kWh for the prototype and low cost solar ORC, respectively. The sensitivity analysis was carried out in order to find the influencing economic parameters for the change in NPV. Finally, the sustainability index was calculated to assess the sustainable development of the solar ORC system. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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634 KiB

Open AccessArticle

A Method to Derive the Definition of Generalized Entropy from Generalized Exergy for Any State in Many-Particle Systems

by Pierfrancesco Palazzo

Entropy 2015, 17(4), 2025-2038; https://doi.org/10.3390/e17042025 - 7 Apr 2015

Cited by 4 | Viewed by 6677

Abstract

The literature reports the proofs that entropy is an inherent property of any system in any state and governs thermal energy, which depends on temperature and is transferred by heat interactions. A first novelty proposed in the present study is that mechanical energy, [...] Read more.

The literature reports the proofs that entropy is an inherent property of any system in any state and governs thermal energy, which depends on temperature and is transferred by heat interactions. A first novelty proposed in the present study is that mechanical energy, determined by pressure and transferred by work interactions, is also characterized by the entropy property. The second novelty is that a generalized definition of entropy relating to temperature, chemical potential and pressure of many-particle systems, is established to calculate the thermal, chemical and mechanical entropy contribution due to heat, mass and work interactions. The expression of generalized entropy is derived from generalized exergy, which in turn depends on temperature, chemical potential and pressure of the system, and by the entropy-exergy relationship constituting the basis of the method adopted to analyze the available energy and its transfer interactions with a reference system which may be external or constitute a subsystem. This method is underpinned by the Second Law statement enunciated in terms of existence and uniqueness of stable equilibrium for each value of energy content of the system. The equality of chemical potential and equality of pressure are assumed, in addition to equality of temperature, to be necessary conditions for stable equilibrium. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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768 KiB

Open AccessArticle

Thermodynamic Analysis of a Waste Heat Driven Vuilleumier Cycle Heat Pump

by Yingbai Xie and Xuejie Sun

Entropy 2015, 17(3), 1452-1465; https://doi.org/10.3390/e17031452 - 20 Mar 2015

Cited by 7 | Viewed by 7633

Abstract

A Vuilleumier (VM) cycle heat pump is a closed gas cycle driven by heat energy. It has the highest performance among all known heat driven technologies. In this paper, two thermodynamic analyses, including energy and exergy analysis, are carried out to evaluate the [...] Read more.

A Vuilleumier (VM) cycle heat pump is a closed gas cycle driven by heat energy. It has the highest performance among all known heat driven technologies. In this paper, two thermodynamic analyses, including energy and exergy analysis, are carried out to evaluate the application of a VM cycle heat pump for waste heat utilization. For a prototype VM cycle heat pump, equations for theoretical and actual cycles are established. Under the given conditions, the exergy efficiency for the theoretical cycle is 0.23 compared to 0.15 for the actual cycle. This is due to losses taking place in the actual cycle. Reheat losses and flow friction losses account for almost 83% of the total losses. Investigation of the effect of heat source temperature, cycle pressure and speed on the exergy efficiency indicate that the low temperature waste heat is a suitable heat source for a VM cycle heat pump. The selected cycle pressure should be higher than 100 MPa, and 200–300 rpm is the optimum speed. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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1993 KiB

Open AccessArticle

A Comparative Study on Energy and Exergy Analyses of a CI Engine Performed with Different Multiple Injection Strategies at Part Load: Effect of Injection Pressure

by Muammer Özkan

Entropy 2015, 17(1), 244-263; https://doi.org/10.3390/e17010244 - 12 Jan 2015

Cited by 34 | Viewed by 7567

Abstract

In this study, a four stroke four cylinder direct injection CI engine was run using three different injection pressures. In all measurements, the fuel quantity per cycle, the pre injection and main injection timing, the boost pressure and the engine speed were kept [...] Read more.

In this study, a four stroke four cylinder direct injection CI engine was run using three different injection pressures. In all measurements, the fuel quantity per cycle, the pre injection and main injection timing, the boost pressure and the engine speed were kept constant. The motor tests were performed under 130, 140 and 150 MPa rail pressure. During the theoretical part of the study, combustion, emission, energy and exergy analysis were made using the test results. An increase in the injection pressure increases combustion efficiency. The results show that combustion efficiency is not enough by itself, because the increase in the power need of the injection pump, decreases the thermal efficiency. The increase in the combustion temperature, increases the cooling loss and decreases the exergetic efficiency. In addition, the NO_x emissions increased by 12% and soot emissions decreased 44% via increasing injection pressure by 17%. The thermal and exergetic efficiencies are found inversely proportional with injection pressure. Exergy destruction is found independent of the injection pressure and its value is obtained as ~6%. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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870 KiB

Open AccessArticle

Energy Analysis and Multi-Objective Optimization of an Internal Combustion Engine-Based CHP System for Heat Recovery

by Abdolsaeid Ganjehkaviri and Mohammad Nazri Mohd Jaafar

Entropy 2014, 16(11), 5633-5653; https://doi.org/10.3390/e16115633 - 27 Oct 2014

Cited by 14 | Viewed by 6859

Abstract

A comprehensive thermodynamic study is conducted of a diesel based Combined Heat and Power (CHP) system, based on a diesel engine and an Organic Rankine Cycle (ORC). Present research covers both energy and exergy analyses along with a multi-objective optimization. In order to [...] Read more.

A comprehensive thermodynamic study is conducted of a diesel based Combined Heat and Power (CHP) system, based on a diesel engine and an Organic Rankine Cycle (ORC). Present research covers both energy and exergy analyses along with a multi-objective optimization. In order to determine the irreversibilities in each component of the CHP system and assess the system performance, a complete parametric study is performed to investigate the effects of major design parameters and operating conditions on the system’s performance. The main contribution of the current research study is to conduct both exergy and multi-objective optimization of a system using different working fluid for low-grade heat recovery. In order to conduct the evolutionary based optimization, two objective functions are considered in the optimization; namely the system exergy efficiency, and the total cost rate of the system, which is a combination of the cost associated with environmental impact and the purchase cost of each component. Therefore, in the optimization approach, the overall cycle exergy efficiency is maximized satisfying several constraints while the total cost rate of the system is minimized. To provide a better understanding of the system under study, the Pareto frontier is shown for multi-objective optimization and also an equation is derived to fit the optimized point. In addition, a closed form relationship between exergy efficiency and total cost rate is derived. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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859 KiB

Open AccessArticle

Performance Degradation Assessment of Rolling Element Bearings Based on an Index Combining SVD and Information Exergy

by Bin Zhang, Lijun Zhang, Jinwu Xu and Pingfeng Wang

Entropy 2014, 16(10), 5400-5415; https://doi.org/10.3390/e16105400 - 16 Oct 2014

Cited by 15 | Viewed by 7190

Abstract

Performance degradation assessment of rolling element bearings is vital for the reliable and cost-efficient operation and maintenance of rotating machines, especially for the implementation of condition-based maintenance (CBM). For robust degradation assessment of rolling element bearings, uncertainties such as those induced from usage [...] Read more.

Performance degradation assessment of rolling element bearings is vital for the reliable and cost-efficient operation and maintenance of rotating machines, especially for the implementation of condition-based maintenance (CBM). For robust degradation assessment of rolling element bearings, uncertainties such as those induced from usage variations or sensor errors must be taken into account. This paper presents an information exergy index for bearing performance degradation assessment that combines singular value decomposition (SVD) and the information exergy method. Information exergy integrates condition monitoring information of multiple instants and multiple sensors, and thus performance degradation assessment uncertainties are reduced and robust degradation assessment results can be obtained using the proposed index. The effectiveness and robustness of the proposed information exergy index are validated through experimental case studies. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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1731 KiB

Open AccessArticle

Progress in the Prediction of Entropy Generation in Turbulent Reacting Flows Using Large Eddy Simulation

by Mehdi Safari, Fatemeh Hadi and M. Reza H. Sheikhi

Entropy 2014, 16(10), 5159-5177; https://doi.org/10.3390/e16105159 - 26 Sep 2014

Cited by 23 | Viewed by 7578

Abstract

An overview is presented of the recent developments in the application of large eddy simulation (LES) for prediction and analysis of local entropy generation in turbulent reacting flows. A challenging issue in such LES is subgrid-scale (SGS) modeling of filtered entropy generation terms. [...] Read more.

An overview is presented of the recent developments in the application of large eddy simulation (LES) for prediction and analysis of local entropy generation in turbulent reacting flows. A challenging issue in such LES is subgrid-scale (SGS) modeling of filtered entropy generation terms. An effective closure strategy, recently developed, is based on the filtered density function (FDF) methodology with inclusion of entropy variations. This methodology, titled entropy FDF (En-FDF), is the main focus of this article. The En-FDF has been introduced as the joint velocity-scalar-turbulent frequency-entropy FDF and the marginal scalar-entropy FDF. Both formulations contain the chemical reaction and its entropy generation effects in closed forms. The former constitutes the most comprehensive form of the En-FDF and provides closure for all of the unclosed terms in LES transport equations. The latter is the marginal En-FDF and accounts for entropy generation effects, as well as scalar-entropy statistics. The En-FDF methodologies are described, and some of their recent predictions of entropy statistics and entropy generation in turbulent shear flows are presented. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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999 KiB

Open AccessArticle

Exergetic and Thermoeconomic Analyses of Solar Air Heating Processes Using a Parabolic Trough Collector

by Miguel Ángel Hernández-Román, Alejandro Manzano-Ramírez, Jorge Pineda-Piñón and Jorge Ortega-Moody

Entropy 2014, 16(8), 4612-4625; https://doi.org/10.3390/e16084612 - 18 Aug 2014

Cited by 12 | Viewed by 6251

Abstract

This paper presents a theoretical and practical analysis of the application of the thermoeconomic method. A furnace for heating air is evaluated using the methodology. The furnace works with solar energy, received from a parabolic trough collector and with electricity supplied by an [...] Read more.

This paper presents a theoretical and practical analysis of the application of the thermoeconomic method. A furnace for heating air is evaluated using the methodology. The furnace works with solar energy, received from a parabolic trough collector and with electricity supplied by an electric power utility. The methodology evaluates the process by the first and second law of thermodynamics as the first step then the cost analysis is applied for getting the thermoeconomic cost. For this study, the climatic conditions of the city of Queretaro (Mexico) are considered. Two periods were taken into account: from July 2006 to June 2007 and on 6 January 2011. The prototype, located at CICATA-IPN, Qro, was analyzed in two different scenarios i.e., with 100% of electricity and 100% of solar energy. The results showed that thermoeconomic costs for the heating process with electricity, inside the chamber, are less than those using solar heating. This may be ascribed to the high cost of the materials, fittings, and manufacturing of the solar equipment. Also, the influence of the mass flow, aperture area, length and diameter of the receiver of the solar prototype is a parameter for increasing the efficiency of the prototype in addition to the price of manufacturing. The optimum design parameters are: length is 3 to 5 m, mass flow rate is 0.03 kg/s, diameter of the receiver is around 10 to 30 mm and aperture area is 3 m². Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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722 KiB

Open AccessArticle

Methods of Evaluating Thermodynamic Properties of Landscape Cover Using Multispectral Reflected Radiation Measurements by the Landsat Satellite

by Yuriy Puzachenko, Robert Sandlersky and Alexey Sankovski

Entropy 2013, 15(9), 3970-3982; https://doi.org/10.3390/e15093970 - 23 Sep 2013

Cited by 21 | Viewed by 5870

Abstract

The paper discusses methods of evaluating thermodynamic properties of landscape cover based on multi-spectral measurements by the Landsat satellites. Authors demonstrate how these methods could be used for studying functionality of landscapes and for spatial interpolation of Flux NET system measurements. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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731 KiB

Open AccessArticle

Exergetic and Parametric Study of a Solar Aided Coal-Fired Power Plant

by Rongrong Zhai, Yong Zhu, Yongping Yang, Kaiyu Tan and Eric Hu

Entropy 2013, 15(3), 1014-1034; https://doi.org/10.3390/e15031014 - 11 Mar 2013

Cited by 33 | Viewed by 7862

Abstract

A solar-aided coal-fired power plant realizes the integration of a fossil fuel (coal or gas) and clean energy (solar). In this paper, a conventional 600 MW coal-fired power plant and a 600 MW solar-aided coal-fired power plant have been taken as the study [...] Read more.

A solar-aided coal-fired power plant realizes the integration of a fossil fuel (coal or gas) and clean energy (solar). In this paper, a conventional 600 MW coal-fired power plant and a 600 MW solar-aided coal-fired power plant have been taken as the study case to understand the merits of solar-aided power generation (SAPG) technology. The plants in the case study have been analyzed by using the First and Second Laws of Thermodynamics principles. The solar irradiation and load ratio have been considered in the analysis. We conclude that if the solar irradiation was 925 W/m² and load ratio of the SAPG plant was 100%, the exergy efficiency would be 44.54% and the energy efficiency of the plant (46.35%). It was found that in the SAPG plant the largest exergy loss was from the boiler, which accounted for about 76.74% of the total loss. When the load ratio of the unit remains at 100%, and the solar irradiation varies from 500 W/m² to 1,100 W/m², the coal savings would be in the range of 8.6 g/kWh to 15.8 g/kWh. If the solar irradiation were kept at 925 W/m² while the load ratio of the plant changed from 30% to 100%, the coal savings could be in the range of 11.99 g/kWh to 13.75 g/kWh. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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934 KiB

Open AccessArticle

Using Exergy to Correlate Energy Research Investments and Efficiencies: Concept and Case Studies

by Marc A. Rosen

Entropy 2013, 15(1), 262-286; https://doi.org/10.3390/e15010262 - 16 Jan 2013

Cited by 16 | Viewed by 6511

Abstract

The use of exergy to correlate energy-utilization efficiencies and energy research investments is described. Specifically, energy and exergy losses are compared with energy research and development expenditures, demonstrating that the latter correlates with energy losses, even though it would be more sensible to [...] Read more.

The use of exergy to correlate energy-utilization efficiencies and energy research investments is described. Specifically, energy and exergy losses are compared with energy research and development expenditures, demonstrating that the latter correlates with energy losses, even though it would be more sensible to allocate energy research and development funding in line with exergy losses, as they represent the actual deviation of efficiency from the ideal. The methodology is outlined and illustrated with two case studies. The case studies consider the province of Ontario, Canada and the United States. The investigation utilizes data on the energy utilization in a country or region, including flows of energy and exergy through the main sectors of the economy. The results are expected to be of use to government and public authorities that administer research and development funding and resources and should help improve the effectiveness of such investments. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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776 KiB

Open AccessArticle

Electro-Kinetic Pumping with Slip Irreversibility in Heat Exchange of CSP-Powered Bio-Digester Assemblies

by Emmanuel O.B. Ogedengbe and Marc A. Rosen

Entropy 2012, 14(12), 2439-2455; https://doi.org/10.3390/e14122439 - 4 Dec 2012

Cited by 5 | Viewed by 6118

Abstract

Parametric studies of the effects of slip irreversibility in concentrating solar power (CSP)-powered bio-digester assemblies are investigated. Complexities regarding the identification of the appropriate electro-kinetic phenomena for certain electrolyte phases are reviewed. The application of exergy analysis to the design of energy conversion [...] Read more.

Parametric studies of the effects of slip irreversibility in concentrating solar power (CSP)-powered bio-digester assemblies are investigated. Complexities regarding the identification of the appropriate electro-kinetic phenomena for certain electrolyte phases are reviewed. The application of exergy analysis to the design of energy conversion devices, like solar thermal collectors, for the required heat of formation in a downdraft waste food bio-digester, is discussed. Thermal management in the silicon-based substrate of the energy system is analyzed. The rectangular-shaped micro-channels are simulated with a finite-volume, staggered coupling of the pressure-velocity fields. Entropy generation transport within the energy system is determined and coupled with the solution procedure. Consequently, the effects of channel size perturbation, Reynolds number, and pressure ratios on the thermal performance and exergy destruction are presented. A comparative analysis of the axial heat conduction for thermal management in energy conversion devices is proposed. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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349 KiB

Open AccessArticle

Utilizing the Exergy Concept to Address Environmental Challenges of Electric Systems

by Cornelia A. Bulucea, Marc A. Rosen, Doru A. Nicola, Nikos E. Mastorakis and Carmen A. Bulucea

Entropy 2012, 14(10), 1894-1914; https://doi.org/10.3390/e14101894 - 11 Oct 2012

Cited by 1 | Viewed by 6017

Abstract

Theoretically, the concepts of energy, entropy, exergy and embodied energy are founded in the fields of thermodynamics and physics. Yet, over decades these concepts have been applied in numerous fields of science and engineering, playing a key role in the analysis of processes, [...] Read more.

Theoretically, the concepts of energy, entropy, exergy and embodied energy are founded in the fields of thermodynamics and physics. Yet, over decades these concepts have been applied in numerous fields of science and engineering, playing a key role in the analysis of processes, systems and devices in which energy transfers and energy transformations occur. The research reported here aims to demonstrate, in terms of sustainability, the usefulness of the embodied energy and exergy concepts for analyzing electric devices which convert energy, particularly the electromagnet. This study relies on a dualist view, incorporating technical and environmental dimensions. The information provided by energy assessments is shown to be less useful than that provided by exergy and prone to be misleading. The electromagnet force and torque (representing the driving force of output exergy), accepted as both environmental and technical quantities, are expressed as a function of the electric current and the magnetic field, supporting the view of the necessity of discerning interrelations between science and the environment. This research suggests that a useful step in assessing the viability of electric devices in concert with ecological systems might be to view the magnetic flux density B and the electric current intensity I as environmental parameters. In line with this idea the study encompasses an overview of potential human health risks and effects of extremely low frequency electromagnetic fields (ELF EMFs) caused by the operation of electric systems. It is concluded that exergy has a significant role to play in evaluating and increasing the efficiencies of electrical technologies and systems. This article also aims to demonstrate the need for joint efforts by researchers in electric and environmental engineering, and in medicine and health fields, for enhancing knowledge of the impacts of environmental ELF EMFs on humans and other life forms. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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346 KiB

Open AccessArticle

Optimization of Two-Stage Peltier Modules: Structure and Exergetic Efficiency

by Miguel Angel Olivares-Robles, Federico Vazquez and Cesar Ramirez-Lopez

Entropy 2012, 14(8), 1539-1552; https://doi.org/10.3390/e14081539 - 21 Aug 2012

Cited by 19 | Viewed by 8347

Abstract

In this paper we undertake the theoretical analysis of a two-stage semiconductor thermoelectric module (TEM) which contains an arbitrary and different number of thermocouples, n₁ and n₂, in each stage (pyramid-styled TEM). The analysis is based on a dimensionless entropy [...] Read more.

In this paper we undertake the theoretical analysis of a two-stage semiconductor thermoelectric module (TEM) which contains an arbitrary and different number of thermocouples, n₁ and n₂, in each stage (pyramid-styled TEM). The analysis is based on a dimensionless entropy balance set of equations. We study the effects of n₁ and n₂, the flowing electric currents through each stage, the applied temperatures and the thermoelectric properties of the semiconductor materials on the exergetic efficiency. Our main result implies that the electric currents flowing in each stage must necessarily be different with a ratio about 4.3 if the best thermal performance and the highest temperature difference possible between the cold and hot side of the device are pursued. This fact had not been pointed out before for pyramid-styled two stage TEM. The ratio n₁/n₂ should be about 8. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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574 KiB

Open AccessArticle

Potential and Evolution of Compressed Air Energy Storage: Energy and Exergy Analyses

by Young-Min Kim, Jang-Hee Lee, Seok-Joon Kim and Daniel Favrat

Entropy 2012, 14(8), 1501-1521; https://doi.org/10.3390/e14081501 - 10 Aug 2012

Cited by 156 | Viewed by 16782

Abstract

Energy storage systems are increasingly gaining importance with regard to their role in achieving load levelling, especially for matching intermittent sources of renewable energy with customer demand, as well as for storing excess nuclear or thermal power during the daily cycle. Compressed air [...] Read more.

Energy storage systems are increasingly gaining importance with regard to their role in achieving load levelling, especially for matching intermittent sources of renewable energy with customer demand, as well as for storing excess nuclear or thermal power during the daily cycle. Compressed air energy storage (CAES), with its high reliability, economic feasibility, and low environmental impact, is a promising method for large-scale energy storage. Although there are only two large-scale CAES plants in existence, recently, a number of CAES projects have been initiated around the world, and some innovative concepts of CAES have been proposed. Existing CAES plants have some disadvantages such as energy loss due to dissipation of heat of compression, use of fossil fuels, and dependence on geological formations. This paper reviews the main drawbacks of the existing CAES systems and presents some innovative concepts of CAES, such as adiabatic CAES, isothermal CAES, micro-CAES combined with air-cycle heating and cooling, and constant-pressure CAES combined with pumped hydro storage that can address such problems and widen the scope of CAES applications, by energy and exergy analyses. These analyses greatly help us to understand the characteristics of each CAES system and compare different CAES systems. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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738 KiB

Open AccessArticle

Ecological Economic Evaluation Based on Emergy as Embodied Cosmic Exergy: A Historical Study for the Beijing Urban Ecosystem 1978–2004

by Jiang Mei Ming, Chen Zhan-Ming, Zhang Bo, Li Shuang Cheng, Xia Xiao Hua, Zhou Shi Yi and Zhou Jiang Bo

Entropy 2010, 12(7), 1696-1720; https://doi.org/10.3390/e12071696 - 29 Jun 2010

Cited by 12 | Viewed by 10722

Abstract

For ecological economic evaluation based on the unified biophysical matrix this research illustrates an updated emergy synthesis in terms of embodied cosmic exergy instead of embodied solar energy, which successes the foundation of systems ecological theory but changes the starting point for the [...] Read more.

For ecological economic evaluation based on the unified biophysical matrix this research illustrates an updated emergy synthesis in terms of embodied cosmic exergy instead of embodied solar energy, which successes the foundation of systems ecological theory but changes the starting point for the estimation from simply the sun to the cosmos. According to the modified definition implicating explicit scarcity and strict additivity based on the fundamental thermodynamics laws, the updated emergy approach overcomes the confusable and intractable deficiencies of traditional one and shows firmer theoretical basis as well as better applicability. As a case study for the regional socio-economic ecosystem, a cosmic emergy based ecological economic evaluation of the Beijing urban ecosystem during the period 1978-2004 is presented. The local and external resources supporting the concerned ecosystem are accounted and analyzed in a common unit, i.e., cosmic Joule, according to which a series of indicators are applied to reveal its evolutional characteristics through five aspects as emergy structure, emergy intensity, emergy welfare, environmental impacts, and degree of exploitation and economic efficiency. During the analyzed period, the major emergy source sustaining the operation of the ecosystem had changed from the renewable resources exploited locally to the nonrenewable resources purchased from outside. Emergy intensity for the Beijing urban ecosystem kept rising owing to the continuous investment of resources, which not only improved the living standard but also intensified the environmental pressure. Moreover, the increase of exploitation degree was accompanied with the decline of economic efficiency, while the rising emergy investment ratio implicates that Beijing was at the risks of resources shortage and high dependence on external resources Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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6551 KiB

Open AccessArticle

Multi-Criteria Evaluation of Energy Systems with Sustainability Considerations

by Christos A. Frangopoulos and Despoina E. Keramioti

Entropy 2010, 12(5), 1006-1020; https://doi.org/10.3390/e12051006 - 27 Apr 2010

Cited by 40 | Viewed by 10168

Abstract

A multi-criteria approach is presented for the assessment of alternative means for covering the energy needs (electricity and heat) of an industrial unit, taking into consideration sustainability aspects. The procedure is first described in general terms: proper indicators are defined; next they are [...] Read more.

A multi-criteria approach is presented for the assessment of alternative means for covering the energy needs (electricity and heat) of an industrial unit, taking into consideration sustainability aspects. The procedure is first described in general terms: proper indicators are defined; next they are grouped in order to form sub-indices, which are then used to determine the composite sustainability index. The procedure is applied for the evaluation of three alternative systems. The three systems are placed in order of preference, which depends on the criteria used. In addition to conclusions reached as a result of the particular case study, recommendations for future work are given. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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310 KiB

Open AccessArticle

Air Conditioning Systems from a 2nd Law Perspective

by Luigi Marletta

Entropy 2010, 12(4), 859-877; https://doi.org/10.3390/e12040859 - 13 Apr 2010

Cited by 20 | Viewed by 13514

Abstract

In this paper exergy analysis is used to assess the performance of the three most common air conditioning plant schemes: all-air, dual-duct and fan-coil systems. The results are presented in terms of flow diagrams to provide a clear picture of the exergy flow [...] Read more.

In this paper exergy analysis is used to assess the performance of the three most common air conditioning plant schemes: all-air, dual-duct and fan-coil systems. The results are presented in terms of flow diagrams to provide a clear picture of the exergy flow across the systems. The most relevant outcomes are that the air cooling and dehumidification is the process most responsible for the exergy loss and that the exergy efficiency of the overall systems is rather low; thus the quest for more appropriate technologies. Solar-assisted air-conditioning is also discussed, outlining the possibilities and the constraints. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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310 KiB

Open AccessArticle

Application of Thermoeconomics to Industrial Ecology

by Antonio Valero, Sergio Usón, César Torres and Alicia Valero

Entropy 2010, 12(3), 591-612; https://doi.org/10.3390/e12030591 - 22 Mar 2010

Cited by 62 | Viewed by 12508

Abstract

Industrial Ecology involves the transformation of industrial processes from linear to closed loop systems: matter and energy flows which were initially considered as wastes become now resources for existing or new processes. In this paper, Thermoeconomics, commonly used for the optimization and diagnosis [...] Read more.

Industrial Ecology involves the transformation of industrial processes from linear to closed loop systems: matter and energy flows which were initially considered as wastes become now resources for existing or new processes. In this paper, Thermoeconomics, commonly used for the optimization and diagnosis of energy systems, is proposed as a tool for the characterization of Industrial Ecology. Thermoeconomics is based on the exergy analysis (Thermodynamics) but goes further by introducing the concepts of purpose and cost (Economics). It is presented in this study as a systematic and general approach for the analysis of waste flow integration. The formulation is based on extending the thermoeconomic process of the cost formation of wastes in order to consider their use as input for other processes. Consequently, it can be applied to important Industrial Ecology issues such as identification of integration possibilities and efficiency improvement, quantification of benefits obtained by integration, or determination of fair prices based on physical roots. The capability of the methodology is demonstrated by means of a case study based on the integration of a power plant, a cement kiln and a gas-fired boiler. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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447 KiB

Open AccessArticle

Combined Effects of Pipe Diameter, Reynolds Number and Wall Heat Flux and on Flow, Heat Transfer and Second-Law Characteristics of Laminar-Transitional Micro-Pipe Flows

by A. Alper Ozalp

Entropy 2010, 12(3), 445-472; https://doi.org/10.3390/e12030445 - 9 Mar 2010

Cited by 7 | Viewed by 11534

Abstract

Fluid flow, heat transfer and entropy generation characteristics of micro-pipes are investigated computationally by considering the simultaneous effects of pipe diameter, wall heat flux and Reynolds number in detail. Variable fluid property continuity, Navier-Stokes and energy equations are numerically handled for wide ranges [...] Read more.

Fluid flow, heat transfer and entropy generation characteristics of micro-pipes are investigated computationally by considering the simultaneous effects of pipe diameter, wall heat flux and Reynolds number in detail. Variable fluid property continuity, Navier-Stokes and energy equations are numerically handled for wide ranges of pipe diameter (d = 0.50–1.00 mm), wall heat flux (q^''= 1000–2000 W/m²) and Reynolds number (Re = 1 – 2000), where the relative roughness is kept constant at e/d = 0.001 in the complete set of the scenarios considered. Computations indicated slight shifts in velocity profiles from the laminar character at Re = 500 with the corresponding shape factor (H) and intermittency values (γ) of H = 3.293→3.275 and γ = 0.041→0.051 (d = 1.00→0.50 mm). Moreover, the onset of transition was determined to move down to Re_tra= 1,656, 1,607, 1,491, 1,341 and 1,272 at d = 1.00, 0.90, 0.75, 0.60 and 0.50 mm, respectively. The impacts of pipe diameter on friction mechanism and heat transfer rates are evaluated to become more significant at high Reynolds numbers, resulting in the rise of energy loss data at the identical conditions as well. In cases with low pipe diameter and high Reynolds number, wall heat flux is determined to promote the magnitude of local thermal entropy generation rates. Local Bejan numbers are inspected to rise with wall heat flux at high Reynolds numbers, indicating that the elevating role of wall heat flux on local thermal entropy generation is dominant to the suppressing function of Reynolds number on local thermal entropy generation. Cross-sectional total entropy generation is computed to be most influenced by pipe diameter at high wall heat flux and low Reynolds numbers. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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136 KiB

Open AccessArticle

Entropy Transport Equation in Large Eddy Simulation for Exergy Analysis of Turbulent Combustion Systems

by Mehdi Safari, M. Reza H. Sheikhi, Mohammad Janbozorgi and Hameed Metghalchi

Entropy 2010, 12(3), 434-444; https://doi.org/10.3390/e12030434 - 8 Mar 2010

Cited by 33 | Viewed by 10240

Abstract

The transport equation of entropy is introduced in large eddy simulation to perform exergy analysis of turbulent combustion systems. The sources of exergy destruction can be evaluated by analyzing entropy generation terms, which appear in unclosed forms in this equation. The closure is [...] Read more.

The transport equation of entropy is introduced in large eddy simulation to perform exergy analysis of turbulent combustion systems. The sources of exergy destruction can be evaluated by analyzing entropy generation terms, which appear in unclosed forms in this equation. The closure is based on the filtered density function (FDF) methodology. The primary advantage of FDF is that chemical reaction and its entropy generation effects appear in closed forms. This methodology involves a stochastic model, which is being developed to account for the subgrid scale transport of entropy. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

250 KiB

Open AccessArticle

Second-Law Analysis to Improve the Energy Efficiency of Screw Liquid Chillers

by Tzong-Shing Lee

Entropy 2010, 12(3), 375-389; https://doi.org/10.3390/e12030375 - 4 Mar 2010

Cited by 21 | Viewed by 10926

Abstract

This work applies the second-law analysis of thermodynamics to quantify the exergy destruction of the components of screw liquid chiller, and to identify the potential for each component to contribute to improve the overall energy efficiency of the system. Three screw liquid chiller [...] Read more.

This work applies the second-law analysis of thermodynamics to quantify the exergy destruction of the components of screw liquid chiller, and to identify the potential for each component to contribute to improve the overall energy efficiency of the system. Three screw liquid chiller units were built to demonstrate the feasibility of the model presented herein. Unit A was a 100 RT water-cooled screw liquid chiller. Unit B was modified from Unit A by switching the old condenser for a new one with a greater heat transfer, and Unit C was modified from Unit B by exchanging the compressor for a more efficient one. The results indicate that the compressor has the largest potential to improve energy efficiency, followed in order by the condenser, and then the evaporator. The second law analysis may help engineers to focus on the components with higher exergy destruction and quantify the extent to which modifying such components can influence, favorably or unfavorably, the performance of other components of the screw liquid chiller. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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1411 KiB

Open AccessArticle

Improvement of Energy Conversion/Utilization by Exergy Analysis: Selected Cases for Non-Reactive and Reactive Systems

by Daniele Fiaschi and Giampaolo Manfrida

Entropy 2010, 12(2), 243-261; https://doi.org/10.3390/e12020243 - 5 Feb 2010

Cited by 6 | Viewed by 10437

Abstract

Exergy analysis is a powerful and systematic tool for the improvement of energy systems, with many possible applications in both conversion and utilization of energy. Here we present selected applications, with a special attention to renewable energy systems (solar), covering both design and [...] Read more.

Exergy analysis is a powerful and systematic tool for the improvement of energy systems, with many possible applications in both conversion and utilization of energy. Here we present selected applications, with a special attention to renewable energy systems (solar), covering both design and operation/control. After these applications to non-reactive systems, potential ways of reducing the large irreversibilities connected to reactive systems (combustion) are considered, with special reference to chemically-recuperated gas turbine cycles and topping high-temperature fuel cells. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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294 KiB

Open AccessArticle

Using Exergy to Understand and Improve the Efficiency of Electrical Power Technologies

by Marc A. Rosen and Cornelia Aida Bulucea

Entropy 2009, 11(4), 820-835; https://doi.org/10.3390/e11040820 - 6 Nov 2009

Cited by 91 | Viewed by 13539

Abstract

The benefits are demonstrated of using exergy to understand the efficiencies of electrical power technologies and to assist improvements. Although exergy applications in power systems and electrical technology are uncommon, exergy nevertheless identifies clearly potential reductions in thermodynamic losses and efficiency improvements. Various [...] Read more.

The benefits are demonstrated of using exergy to understand the efficiencies of electrical power technologies and to assist improvements. Although exergy applications in power systems and electrical technology are uncommon, exergy nevertheless identifies clearly potential reductions in thermodynamic losses and efficiency improvements. Various devices are considered, ranging from simple electrical devices to generation systems for electrical power and for multiple products including electricity, and on to electrically driven. The insights provided by exergy are shown to be more useful than those provided by energy, which are sometimes misleading. Exergy is concluded to have a significant role in assessing and improving the efficiencies of electrical power technologies and systems, and provides a useful tool for engineers and scientists as well as decision and policy makers. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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219 KiB

Open AccessArticle

Exergy as a Useful Variable for Quickly Assessing the Theoretical Maximum Power of Salinity Gradient Energy Systems

by Raynald Labrecque

Entropy 2009, 11(4), 798-806; https://doi.org/10.3390/e11040798 - 5 Nov 2009

Cited by 8 | Viewed by 9428

Abstract

It is known that mechanical work, and in turn electricity, can be produced from a difference in the chemical potential that may result from a salinity gradient. Such a gradient may be found, for instance, in an estuary where a stream of soft [...] Read more.

It is known that mechanical work, and in turn electricity, can be produced from a difference in the chemical potential that may result from a salinity gradient. Such a gradient may be found, for instance, in an estuary where a stream of soft water is flooding into a sink of salty water which we may find in an ocean, gulf or salt lake. Various technological approaches are proposed for the production of energy from a salinity gradient between a stream of soft water and a source of salty water. Before considering the implementation of a typical technology, it is of utmost importance to be able to compare various technological approaches, on the same basis, using the appropriate variables and mathematical formulations. In this context, exergy balance can become a very useful tool for an easy and quick evaluation of the maximum thermodynamic work that can be produced from energy systems. In this short paper, we briefly introduce the use of exergy for enabling us to easily and quickly assess the theoretical maximum power or ideal reversible work we may expect from typical salinity gradient energy systems. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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216 KiB

Open AccessArticle

Determination of the Real Loss of Power for a Condensing and a Backpressure Turbine by Means of Second Law Analysis

by Henrik Holmberg, Pekka Ruohonen and Pekka Ahtila

Entropy 2009, 11(4), 702-712; https://doi.org/10.3390/e11040702 - 30 Oct 2009

Cited by 29 | Viewed by 13322

Abstract

All real processes generate entropy and the power/exergy loss is usually determined by means of the Gouy-Stodola law. If the system only exchanges heat at the environmental temperature, the Gouy-Stodola law gives the correct loss of power. However, most industrial processes exchange heat [...] Read more.

All real processes generate entropy and the power/exergy loss is usually determined by means of the Gouy-Stodola law. If the system only exchanges heat at the environmental temperature, the Gouy-Stodola law gives the correct loss of power. However, most industrial processes exchange heat at higher or lower temperatures than the actual environmental temperature. When calculating the real loss of power in these cases, the Gouy-Stodola law does not give the correct loss if the actual environmental temperature is used. The first aim of this paper is to show through simple steam turbine examples that the previous statement is true. The second aim of the paper is to define the effective temperature to calculate the real power loss of the system with the Gouy-Stodola law, and to apply it to turbine examples. Example calculations also show that the correct power loss can be defined if the effective temperature is used instead of the real environmental temperature. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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212 KiB

Open AccessArticle

Thermoeconomic Optimum Operation Conditions of a Solar-driven Heat Engine Model

by Marco A. Barranco-Jiménez, Norma Sánchez-Salas and Marco A. Rosales

Entropy 2009, 11(3), 443-453; https://doi.org/10.3390/e11030443 - 25 Aug 2009

Cited by 25 | Viewed by 10114

Abstract

In the present paper, the thermoeconomic optimization of an endoreversible solardriven heat engine has been carried out by using finite-time/finite-size thermodynamic theory. In the considered heat engine model, the heat transfer from the hot reservoir to the working fluid is assumed to be [...] Read more.

In the present paper, the thermoeconomic optimization of an endoreversible solardriven heat engine has been carried out by using finite-time/finite-size thermodynamic theory. In the considered heat engine model, the heat transfer from the hot reservoir to the working fluid is assumed to be the radiation type and the heat transfer to the cold reservoir is assumed the conduction type. In this work, the optimum performance and two design parameters have been investigated under three objective functions: the power output per unit total cost, the efficient power per unit total cost and the ecological function per unit total cost. The effects of the technical and economical parameters on the thermoeconomic performance have been also discussed under the aforementioned three criteria of performance. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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667 KiB

Open AccessArticle

Imaging Velocimetry Measurements for Entropy Production in a Rotational Magnetic Stirring Tank and Parallel Channel Flow

by Greg F. Naterer and Olusola B. Adeyinka

Entropy 2009, 11(3), 334-350; https://doi.org/10.3390/e11030334 - 23 Jul 2009

Cited by 6 | Viewed by 8840

Abstract

An experimental design is presented for an optical method of measuring spatial variations of flow irreversibilities in laminar viscous fluid motion. Pulsed laser measurements of fluid velocity with PIV (Particle Image Velocimetry) are post-processed to determine the local flow irreversibilities. The experimental technique [...] Read more.

An experimental design is presented for an optical method of measuring spatial variations of flow irreversibilities in laminar viscous fluid motion. Pulsed laser measurements of fluid velocity with PIV (Particle Image Velocimetry) are post-processed to determine the local flow irreversibilities. The experimental technique yields whole-field measurements of instantaneous entropy production with a non-intrusive, optical method. Unlike point-wise methods that give measured velocities at single points in space, the PIV method is used to measure spatial velocity gradients over the entire problem domain. When combined with local temperatures and thermal irreversibilities, these velocity gradients can be used to find local losses of energy availability and exergy destruction. This article focuses on the frictional portion of entropy production, which leads to irreversible dissipation of mechanical energy to internal energy through friction. Such effects are significant in various technological applications, ranging from power turbines to internal duct flows and turbomachinery. Specific problems of a rotational stirring tank and channel flow are examined in this paper. By tracking the local flow irreversibilities, designers can focus on problem areas of highest entropy production to make local component modifications, thereby improving the overall energy efficiency of the system. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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Review

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387 KiB

Open AccessReview

Exergy as a Tool for Ecosystem Health Assessment

by Eugene A. Silow and Andrew V. Mokry

Entropy 2010, 12(4), 902-925; https://doi.org/10.3390/e12040902 - 13 Apr 2010

Cited by 47 | Viewed by 12430

Abstract

Exergy is demonstrated to be a useful measurable parameter reflecting the state of the ecosystem, and allowing estimation of the severity of its anthropogenous damage. Exergy is shown to have advantages such as good theoretical basis in thermodynamics, close relation to information theory, [...] Read more.

Exergy is demonstrated to be a useful measurable parameter reflecting the state of the ecosystem, and allowing estimation of the severity of its anthropogenous damage. Exergy is shown to have advantages such as good theoretical basis in thermodynamics, close relation to information theory, rather high correlation with others ecosystem goal functions and relative ease of computation. Nowadays exergy is often used in ecological assessment. This paper reviews the application of exergy in ecology in the fields of ecological modeling and natural ecosystem monitoring. Special attention is paid to the use of exergy for aquatic ecosystem studies, particularly, assessment of the lake Baikal ecosystem state. Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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332 KiB

Open AccessReview

Optimal Thermodynamics—New Upperbounds

by Michel Feidt

Entropy 2009, 11(4), 529-547; https://doi.org/10.3390/e11040529 - 28 Sep 2009

Cited by 73 | Viewed by 12143

Abstract

This paper reviews how ideas have evolved in this field from the pioneering work of CARNOT right up to the present. The coupling of thermostatics with thermokinetics (heat and mass transfers) and entropy or exergy analysis is illustrated through study of thermomechanical engines [...] Read more.

This paper reviews how ideas have evolved in this field from the pioneering work of CARNOT right up to the present. The coupling of thermostatics with thermokinetics (heat and mass transfers) and entropy or exergy analysis is illustrated through study of thermomechanical engines such as the Carnot heat engine, and internal combustion engines. The benefits and importance of stagnation temperature and irreversibility parameters are underlined. The main situations of constrained (or unconstrained) optimization are defined, discussed and illustrated. The result of this study is a new branch of thermodynamics: Finite Dimensions Optimal Thermodynamics (FDOT). Full article

(This article belongs to the Special Issue Exergy: Analysis and Applications)

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