International Journal of Exergy (15 papers in press)
Towards a better understanding of energy systems using emergy-based exergoeconoenvironmental analysis
by Mortaza Aghbashlo, Marc A. Rosen
Abstract: This paper introduces emergy-based exergoeconoenvironmental analysis, a new methodology for improved understanding of energy systems through simultaneous consideration of thermodynamic, financial, and ecological criteria. A new parameter called exergetic ecological emergy/financial emergy ratio is first introduced. This parameter is then used for deriving emergy-based exergoeconoenvironmental balances for an energy system by combining it with exergy cost concepts. The exergetic ecological emergy/financial emergy ratio for all exergy streams of the system is determined using the SPECO approach. The developed approach is applied to a simple cogeneration system of power and steam to demonstrate its general applicability and robustness. The outcomes of the developed method herein are assessed in comparison with those of emergy-based exergoeconomic and exergoenvironmental methods. Overall, the highest total exergetic ecological emergy/financial emergy ratio (13.0841 sej/sej) is observed in the heat-recovery steam generator followed by the air preheater (10.0379 sej/sej). Even though both emergy-based exergoeconomic and exergoenvironmental methods give the improvement priority first for the combustion chamber, the heat-recovery steam generator is suggested by emergy-based exergoeconoenvironmental analysis. Generally, the hybrid framework developed here appears to be a promising complement to available exergy-based techniques for systematically developing thermodynamically, financially, and ecologically conscious energy systems.
Keywords: Emergy; Exergoeconoenvironmental analysis; Specific exergy costing; Exergy cost .
Energy and Exergy Analyses of Paddy Drying Process in a Vertical Fluidized Bed Dryer
by Binayak Pattanayak, Siba Shankar Mohapatra, Harish Chandra Das
Abstract: This research article focuses on the energy and exergy analysis of paddy drying using Fluidized bed dryer. The energy analysis of paddy drying process is conducted using First law of thermodynamics. The parameters Energy Utilization (EU) and Energy Utilization Ratio (EUR) are determined from the first law analysis. Similarly, second law of thermodynamics is used for the exergy analysis of paddy drying. Exergy analysis is conducted with the help of the parameters like exergy evaporation rate, exergy destruction and exergetic efficiency. Specific Moisture Extraction Rate (SMER) is determined to get the value of moisture vaporization rate per energy consumed for drying. Paddy grains are dried in a batch of 2 kg and 3 kg at 400C, 500C temperature of drying air and drying air velocity of 2 and 3 m/s. From the analysis it is observed that EU, EUR, SMER and exergy destruction decreased and exergetic efficiency increased with drying time. The exergy evaporation rate first increases to a certain value from zero and then decreases continuously. The exergetic efficiency varies from 12.37% to 86.25% whereas EU and EUR varied from 55 J/s to 549 J/s and 0.087 to 0.656 respectively.
Keywords: Energy; Energy Utilization; Energy Utilization Ratio; Exergy; Exergy Destruction; Exergetic Efficiency.
Theoretical investigation of entropy generation effects in nanofluid flow over an inclined stretching cylinder
by Adnan Butt, Asif Ali, Muhammad Nazim Tufail, Amanullah Dar
Abstract: Laminar incompressible boundary layer flow and heat transfer of nanofluid over an inclined stretching cylinder is considered and the entropy effects are theoretically examined during the phenomena. The problem is mathematically modelled and nonlinear partial differential equations are attained. With the help of suitable similarity transformations, these partial differential equations are transformed into nonlinear ordinary differential equations which are numerically solved by utilizing shooting technique with fourth-fifth order Runge-Kutta method. The results obtained are compared with the previously existing literature by considering certain limiting cases. The influence of physical parameters on flow, heat transfer and concentration of nanoparticles are analyzed qualitatively with the use of graphs and tables. Furthermore, the impact of various physical parameters on local entropy generation number and averaged entropy generation number are also presented through graphs. A detailed comprehensive study has been carried out of the problem.
Keywords: Inclined stretching cylinder; nanofluid; entropy generation; mixed convection.
Energy and Exergy Analyses of a Novel Solar PTC Assisted Multi-Generation System
by Olusola Bamisile, MUSTAFA DAGBASI, SERKAN ABBASOGLU
Abstract: In this study, a solar assisted multigeneration system is presented. The exergy and energy performance analyses is the objective of this research. The multigeneration system consists of two Rankine cycles, two absorption cycles and a hot water tank. Solar parabolic trough collectors are used to generate thermal energy from the sun which in turn is used to power the system. The multi-generation system achieves an energy and exergy efficiency of 77% and 49% respectively without solar input. Considering the solar PTC, the efficiencies respectively are 57% for energy and 40% for exergy. The COPs for the absorption cycle and other findings from the study are presented in details in the full paper. Exergy destruction in major components are calculated and parametric studies are done to check the performance of the system under varying global solar irradiance conditions.
Keywords: Absorption cycle; Energy; Exergy; Parabolic Trough Collectors; Rankine cycle; Solar.
Performance evaluation of a mobile air conditioning unit:an exergetic approach
by Huseyin Gunhan Ozcan, Arif Hepbasli, Huseyin Gunerhan
Abstract: This study considers a public bus (having a capacity of 99 passengers and a volume of 69 m3) along with its vapor compressed mobile air conditioning (MAC) unit (utilizing R134a as a refrigerant) together as a low exergy (so-called LowEx) system. The LowEx analysis, which has been mostly applied to buildings, and conventional exergy analyses method are utilized together (coupled up analysis method) to assess the performance of this system for the first time to the best of the authors knowledge. Based on the LowEx analysis, total exergy efficiency and exergy flexibility factor are calculated to be 11.92% and 0.56 for the heating mode and 3.41% and 0.19 for the cooling mode, respectively. Furthermore, through on the conventional exergy analyses, the highest exergy efficiency belongs to condenser with 93.08% in the cooling mode, while it is 93.20% for the water heat exchanger in the heating mode, respectively.
Keywords: LowEx; conventional exergy; public bus; mobile air conditioning; heating and cooling.
Exergy Analysis and Assessment of Performance Criteria for Compressed Air Energy Storage (CAES) Concepts
by Friederike Kaiser, Uwe Krüger
Abstract: Compressed Air Energy Storage (CAES) power plants provide positive and negative power reserves to compensate for an increasing share of intermittent renewable electric energy generation from wind and solar power stations. The compressed air is stored to drive a very efficient open gas turbine. However, enthalpy, a measure of the energy content of compressed air, is close to zero at ambient air temperatures. This indicates that enthalpy underestimates the ability of compressed air to do work and implies low storage efficiencies of the CAES open gas turbine cycle. Thus, in this project, the characterization of different CAES concepts based on exergy in contrast to enthalpy is discussed, including the fuel-driven CAES plants Huntorf and McIntosh and forthcoming concepts.
The CAES energy efficiency defined as caes = Wel,G/(Wel,M + Qfuel), resulting in approximately 42 % for Huntorf and 54 % for McIntosh, is unsuitable for characterizing CAES as an electrical energy storage. Instead, an alternative Round Trip Energy Efficiency rt4 is presented, which can be split up into a compression conversion efficiency cc and a turbine conversion efficiency tc. An exergy-based counterpart is deemed ideal to evaluate the storage properties of CAES. However, the enthalpy-based tc emphasizes the efficient generation characteristics of fuel-driven CAES technology (e.g. McIntosh with over 82 % fuel efficiency of the turbine process as compared to a Carnot value of 75 %).
Keywords: Compressed Air Energy Storage; CAES; Huntorf; energy storage efficiency; exergy; steady state thermodynamics; performance criteria; comparison.
Enhanced exergetic analysis of an olive oil refining plant:
evaluation of the first and second level of exergy destructions
by Elif Bozoglan, Zafer Erbay, Arif Hepbasli, Huseyin Gunerhan
Abstract: Enhanced exergy analysis is built up as a novel modality to specify the origins of irreversibilities and to concentrate substantial improvement potential of components. The scope of this paper is to apply the enhanced exergy analysis to an olive oil refinery plant operated in Izmir, Turkey, that is conducted for the first time to agree the first level (endogenous/exogenous) and the second level (combination of the endogenous/exogenous and unavoidable/avoidable parts studied before) of destructions for exposing substantial efficiencies. With respect to the outcomes of the analysis, the components in the plant mostly have endogenous exergy destruction rates. Besides, the distillation unit has the highest endogenous exergy destruction value of 150.9 kW as the avoidable and unavoidable endogenous sections are 76.85 and 74.08 kW, respectively. Furthermore, the shell & tube economizer has the highest modified (enhanced) exergetic efficiency of 99.9% while the modified performances of plate-heat exchanger and pump (VII) are calculated as.73% and 71.24%, respectively.
Keywords: enhanced exergy; olive oil refining plant; endogenous; exogenous; modified exergetic efficiency.
Energetic and exergetic investigations of an innovative heat recovery exhaust system using a double acting type Stirling engine based on theoretical analysis
by Houda HACHEM, Ramla Gheith, Fethi Aloui, Sébastien DELPRAT, Sébastien PAGANELLI
Abstract: This study aims to predict the feasibility and the performances of an innovative recovery system. It couples a double acting Stirling engine to the exhaust hot gas of internal combustion engines drive shaft. The behavior of a micro-cogeneration system using Stirling engine is investigated. Referring to previous energetic analyses, exergetic model is set up in order to quantify the exergy destruction and efficiencies in each part of the recovery exhaust system. The repartition of the exergy fluxes in each part are determined and represented in Grassmann diagram. Possible solutions to improve the overall exergy efficiency of the micro-cogeneration unit were proposed. The performance of the Stirling engine was evaluated under different operating conditions. Effects of certain parameters including charge pressure, rotational speed, hot exhaust gas temperature and cooling water temperature are systematically studied. The effect of hot-side and cold-side exchange surfaces on the power and efficiency of the Stirling engine as well as on the efficiency of the global micro-cogeneration unit is investigated. The performance of the Stirling engine using three different working fluids: nitrogen N2, helium He and hydrogen H2 is estimated. Results can be useful for scientists and engineers to design an appropriate and efficient micro-cogeneration unit.
Keywords: Micro-cogeneration system; Double acting Stirling engine; exhaust gas; exergy destruction; exergy efficiency.
Perspective on the Ontological Ramifications of the 2nd Law of Thermodynamics
by Yunus Cengel
Abstract: Mass and energy are conserved quantities and are associated with the 1st law of thermodynamics, while entropy and exergy are non-conserved quantities and are associated with the 2nd law. The physical universe as we know it consists of matter and energy, including dark matter and dark energy. As conserved quantities, mass and energy fit into the description of physical entities, but entropy and exergy do not since entropy can be created and exergy can be destroyed. Thus, unlike mass and energy, the properties entropy and exergy are not physical entities although they are closely related to the physical entities mass and energy. Therefore, the 2nd law deals with quantities that are of a different kind of existence a universe in which things come into existence out of nothing and go out of existence into nothing and points to a form of existence that is beyond the physical universe we are familiar with. Extensions are made to other non-material entities such as physical laws, force, free will and life, and parallels are drawn with the glitter of light reflected off diamond. This paper is intended to stimulate discussion on non-conserved quantities like entropy and exergy with philosophical ramifications on existence.
Keywords: Second law; thermodynamics; entropy; exergy; philosophy; ontology; existence; laws of physics; non-conserved quantities.
Entropy generation due to a moving isothermal wavy surface in nanofluid
by Ahmer Mehmood, Sajid Khan, Muhammad Saleem Iqbal
Abstract: The aim of current investigation is to analyze the irreversibility phenomenon, in the presence of nanoparticles in the base fluid, in viscous flow caused by the uniform motion of a wavy plate. The utilized model for the presentation of nanofluid is the Bonjourno model in which the Brownian motion and thermophoresis effects are considered. The non-flat surface texture of the wavy plate does not allow the similarity solution to exist due to which the problem is non-similar in nature. The study of entropy generation phenomenon in such non-similar boundary layer flows is very rare in literature. An implicit finite difference scheme (the Keller-box method) is utilized to obtain the numerical solution and the results have been presented through several graphs. Impact of various controlling parameters, namely, the Brownian motion parameter, the thermophoresis parameter, wavy amplitude, Lewis number, Prandtl, and Brinkman numbers on Bejan number and entropy production number are examined. It is found that entropy production increases by increasing the concentration of nanoparticles.
Keywords: Nanofluid; entropy generation; moving wavy surface; Boungiorno model.
Enhanced exergy analysis of a bubble-pump-driven LiCl-H2O absorption air-conditioning system
by Julia Aman, Paul Henshaw, David Ting
Abstract: A thermally-driven bubble pump can replace the electrical pump in the absorption refrigeration cycle for lifting solution from the absorber to the generator and producing the required refrigerant vapor for the cooling effect. However, the lower efficiency of bubble-pump-driven absorption refrigeration cycle hinders its widespread application. The potential of a bubble-pump-driven LiCl-H2O absorption refrigeration system that can be powered by solar thermal energy or waste heat energy is discussed and analyzed in this study. The new concept of enhanced exergy analysis is integrated in the thermodynamic analyses, which quantifies the available exergy destruction of each component for overall system performance improvement. The analyses uncovered that 80% of the total exergy loss is due to each components own internal irreversibilities, whereas the remaining is through the interaction of the irreversibilities of other components in the system. The analyses revealed that though the highest exergy losses (46%) are in the absorber, priority for improvement should be given to the generator. Furthermore, the exergy losses of the condenser, the evaporator, and the solution heat exchanger are mostly unavoidable and can be reduced by improving the other components of the system.
Keywords: bubble pump; LiCl-H2O; vapor absorption refrigeration; exergy analysis; advanced exergy analysis.
Energy, Exergy and Economic Analysis for ON/OFF Cycle and VFD HVAC Cooling Systems
by Waleed M. Hamanah, Mahmoud Kassas, Ahmet Z. Sahin, Ibrahim El-Amin
Abstract: A comparison of energy, exergy rate and economic analyses for an air conditioning ON/OFF cycle and VFD HVAC systems with heat mass exchange calculation was performed. The study considered several key performance parameters including; energy consumption, energy saving, exergy destruction rate, exergy efficiency, CO2 emission, coefficient of performance (COP), and cost analysis for both HVAC systems. VFD technique significantly improves the air conditioning efficiency, while it has only a small effect on cost. However, in the presence of a VFD both the required cooling energy and the required input power decrease significantly. In addition, the total energy consumption, exergy destruction and CO2 emission are lower when a VFD HVAC is used, as compared with an ON/OFF cycle HVAC system. The total exergy destruction decreases by more than 20%, on average, when a VFD is used when compared with the case of the ON/OFF cycle. Thus, this study reveals that, when a VFD is used, the energy efficiency and exergy efficiency increase by more than 37% and 10%, respectively.
Keywords: Energy Savings; Exergy Destruction; Variable Frequency Drives VFD; ON/OFF Cycle; Heating; Ventilation; and Air Conditioning (HVAC).
Exergetic evaluation of a conceptual design for hydrogen production and seawater desalination using an advanced nuclear reactor as energy source.
by Daniel González Rodríguez, Fernando Roberto De Andrade Lima, Carlos Alberto Brayner De Oliveira Lira, Carlos Rafael García Hernández
Abstract: In this work, a computational model to develop the conceptual design for hydrogen production and seawater desalination based on a modular nuclear reactor as an energy source is presented. The 4-step Cu-Cl process is used to produce hydrogen coupled to the GT-MHR nuclear system through a Brayton cycle for the electrical energy generation. A fraction of the thermal energy from the GT-MHR system is used to reach and maintain the temperature requirements in the Cu-Cl process. The rejected heat from the oxy-decomposition reaction is used to desalinate seawater through a multi-stage process flash. It is employed a chemical process simulator in order to develop a computational model of the proposed system. The global energy and exergy efficiencies of the proposal are 32.47% and 52.20% respectively, producing 0.2190 kg/s of hydrogen and desalinating 4.9492 kg/s of seawater. It is made an estimate of the cost of hydrogen produced using HEEP
Keywords: nuclear hydrogen production; exergy; energy; efficiency; seawater desalination; cost estimative.
Special Issue on: GCGW2018 Exergetic Solutions for Better Performance
Comparative Thermodynamic Performance Assessment of Two-Stage Cycle for Various Refrigerants
by Fatih Yilmaz, Murat ÖZTURK, Resat SELBAS
Abstract: In this paper, the thermodynamic performance evaluations of the two-stage cooling cycle are investigated comparatively for different refrigerants under the same operating conditions. Due to their environmentally friendly properties, CO2, R600, R600a, R161, and R134a are selected as the refrigerants. The change in energy performance coefficient (COPen) and exergy performance coefficient (COPex) of the defined cycle are investigated according to the various indicators, such as reference temperature, gas cooler outlet temperature and pressure. Results are shown that, at the evaporator temperature of -5 oC and the gas cooler outlet temperature of 40 oC , the COPen of the cooling cycle are 1.644, 1.603, 1.452, 2.0356 and 1.928 for the refrigerants CO2, R600, R600a, R161 and R134a, respectively. Furthermore, COPex of the cycle are computed as 25.94%, 15.57%, 14.07%, 19.73% and 18.68% for the same refrigerants in the same order. In addition, the overall exergy destruction rate of the cooling cycle for CO2 refrigerant is calculated as 145.69 kW.
Keywords: CO2; energy; exergy; cooling; refrigerants.
Energy, Exergy, Exergoeconomic, and Exergoenvironmental study of a parabolic trough collector using a converging-diverging receiver tube.
by Eric Chekwube Okonkwo, Tahir Abdul Hussain RATLAMWALA, Muhammad ABID
Abstract: This study presents a novel energy, exergy, exergoeconomic and exergoenvironmental analysis of a parabolic trough solar collector operating with a converging-diverging absorber tube design. The collector is modeled thermally after the experimental results of the Sandia National Laboratory LS-2 collector test using the engineering equation solver. The results of the analysis show that the converging-diverging geometry obtained a mean enhancement in thermal efficiency of 1.13% and 0.49% in exergetic efficiency when compared to the conventional absorber tube. The optical losses with 24.5% accounted for the highest source of exergetic losses while the exergy destruction due to heat transfer between the sun and the absorber accounted for 59.7% at inlet temperatures of 350 K. The exergoeconomic study shows that the cost rate of exergy destruction is seen to decrease from 3.4 - 0.35 $/hr as the inlet temperature increases from 323-650 K. The environmental study yielded an exergoenvironmental impact factor of 0.31 with the values of 2.61, 0.82 and 1.22 for the exergoenvironmental impact coefficient, impact index and impact improvement respectively.
Keywords: parabolic trough collector; converging-diverging; energy; exergy; exergy destruction; exergy loss; exergoeconomic; exergoenvironmental; thermal efficiency; heat transfer.