International Journal of Exergy (44 papers in press)
Thermoeconomic assessment of a waste heat recovery system driven by a marine diesel engine for power and freshwater production
by Yadaleh Aghdoudchaboki, Ahmad Khoshgard, Gholam Reza Salehi, Farivar Fazelpour, Ali Emadi
Abstract: To develop eco-friendly ships, an integrated system with power and fresh water production capabilities is introduced so as to recover waste heat of a marine engine. A thermoeconomic analysis is conducted on the system which consists a marine engine, a multi-effect desalination unit and an organic Rankine cycle. The modelling results for the base case showed that the suggested cycle is capable of 387.95 kW power and 7.04 m3/hr fresh water. In addition, the effects of major design parameters on the system performance is assessed and illustrated. The ORC contributed to the total exergy destruction by 67% while that was 33% for MED unit. Moreover, a two-objective optimisation with total cost rate and exergy efficiency as objective functions is performed to obtain the optimum values of five design parameters. An optimal condition with the exergy efficiency of 35.96% and total cost rate of 2.54 $/hr is introduced as the best trade-off solution.
Keywords: thermoeconomic; waste heat recovery; WHR; marine engine; organic rankine cycle; ORC; multi-effect desalination; MED.
Dynamic reference environment for exergy: a trigeneration system case study
by Wojciech Kostowski, Wodzis?aw Piekarczyk
Abstract: The paper discusses the problem of reference temperature for exergy calculation using an example of a combined cold, heat and power unit integrated with biomass gasification. Depending on the ambient temperature and the demand for heating and cooling, several modes of operation are considered. The performance of the system is evaluated by exergy analysis for various reference temperatures. First, the annual average temperature of 8.5 C is applied. Then, monthly variation of the reference temperature between 0.5 and 18.6C (Katowice, Poland) is considered. It has been shown that a constant reference temperature yields misleading results with numerical error
between 5% for high-temperature media to almost 90% for cooling agents, in
particular for cooling agents, where the useless return water has apparently
more exergy than the cold ice water. In conclusion, a variable reference temperature
is recommended for exergy analysis of systems including cooling or
low-temperature heating agents.
Keywords: exergy; reference environment; CCHP; biomass; gasification; internal combustion engines; absorption chiller; steam engine.
Exergoeconomic Pricing Strategy of Crude Oil Gathering and Transportation System
by Cheng Qinglin
Abstract: Taking a typical oil transfer station in eastern China as an example in this paper, exergy economics theory in algebraic pattern is applied to the energy system of the oil transfer station on the basis of the exergy analysis. By analyzing the cost structure of each equipment and unit, exergy economics equilibrium equation in algebraic pattern can be established. Two different cost allocation methods, extraction method and energy level method, are introduced into the auxiliary equation. Combined with the principle of exergy loss pricing, the unit cost of each exergy loss is calculated. The results show that the energy level method can effectively distinguish the changes of energy quality, which is more suitable for the economic pricing strategy of the oil transfer station gathering and transportation system, and provides a more scientific and effective method and basis for the energy-saving transformation of the oil field gathering and transportation system.
Keywords: crude oil gathering and transportation system; cost structure; cost allocation method; the cost of exergy economics.
Exergy and exergoeconimic analysis and multi-criteria optimization of 1 MW installed CCHP system (a case study in Kashan University)
by Saber Khanmohammadi, Shoaib Khanmohammadi, Hossein Khorasanizadeh
Abstract: The present study deals with exergy and exergo-economic evaluation of a 1 MW combined cooling, heat and power (CCHP) system, composed of a natural gas prime mover internal combustion engine located in the main campus of the University of Kashan, in Kashan, Iran. To retrieve the thermal energy from exhaust gas of the engine and the heat removed by the engine jacket water, shell and tube heat and plate heat exchangers have been incorporated, respectively. The refrigeration unit of the system is consisting of a Li-Br absorption chiller with refrigeration capacity of 200 refrigeration tones (RT). Using appropriate linking between Engineering Equation Solver (EES) and Matlab software, thermal and economic modeling and muti-criteia optimization (MCO) have been performed. A novel approach of the current study is consideration of technical and economical viewpoints simultaneously and applying a multi-objective optimization to find the optimum operating parameters of an installed CCHP system. The optimization results showed that the minimum total exergy destruction rate occurs for the exhaust gas extraction factor of 0.68 which causes 33.52 $/h total cost rate. For this case, among all of the system components the most exergy destruction rate of 1700 kW belongs to the engine. In addition, the results of the genetic algorithm based multi-objective optimization represented that the optimization causes 2.68 $/h decrease in total cost rate and reduction of 4512 kW in exergy destruction rate.
Keywords: Combined cooling; heat and power; Exergy analysis; Thermoeconomic; Multi-criteria optimization.
A comparative assessment of SPECO and MOPSA on costing of exergy destruction
by Cuneyt Uysal, Dilek Ozen, Huseyin Kurt, Ho-Young Kwak
Abstract: This paper presents the comparison of Specific Exergy Costing (SPECO) and Modified Productive Structure Analysis (MOPSA) method to test their abilities on costing of exergy destruction. MOPSA method is applied to a combined supercritical CO2 regenerative cycle and organic Rankine cycle using zeotropic mixtures for gas turbine waste heat recovery system. The results obtained with applying SPECO method to the system are taken from literature. The exergy destruction cost rate of overall system is obtained to be 86.08 $/h and 1113.13 $/h for MOPSA and SPECO methods, respectively. The exergoeconomic factor of overall system is found to be 31.88% for SPECO method, while this value is found to be 85.82% for MOPSA method. The obtained results with applying MOPSA method for exergy destruction cost rate are significantly lower and more consistent compared to the results obtained by SPECO method.
Keywords: SPECO; MOPSA; Thermoeconomics; Exergy Destruction; Organic Rankine Cycle; Supercritical Cycle.
Energy and Exergy Analysis of a PV/Thermal Storage System Design Integrated with Nano-enhanced Phase Changing Material
by Alper Ergün
Abstract: Nanotechnology and heat storage applications are among the most popular fields of the researchers in recent years. In this study, three different CPV/T systems were analyzed experimentally under the same conditions for four days. While no modifications on the CPV were made in the first system, the rear of the panel used in the second system was covered with a phase-changing material (PCM). In the third system, together with PCM, nano-sized aluminum oxide (Al2O3) particle in a weight percentage of 5% was added into the system (namely, nano-enhanced PCM). The experimental analysis revealed that 8% more power output and module efficiency were obtained from the system with the PCM and the nano-enhanced PCM compared to the normal system. These systems which were also designed with a heat storage have an average of 42W thermal energy gain. As the exergy analysis results show, the exergy destruction of the system with the nano-enhanced PCM was found to be lower than that of the PCM system, while exergy efficiency was found to be 14% higher in the former system.
Keywords: Nano-enhanced PCM; heat storage; CPV; photovoltaic-thermal.
Exergy analysis of district energy systems and comparison of their exergetic, energetic and environmental performance
by Ehsan Ahmadian, Ralf-Roman Schmidt
Abstract: This paper investigates the advantages of performing exergy analysis for thermodynamic systems consisting of a district heating network (DHN) by comparing the exergy performance with energetic and environmental performance of three case studies in Austria. Furthermore, the effect of influential parameters such as energy source type, conversion technology, supply/return temperature and reference temperature on exergy performance of the system was investigated. An initial literature review and analysis of the case studies showed that the most influential factor on exergy performance of a system was the type of energy source and its conversion technology. Although lowering the supply temperature of DHN can increase the exergy efficiency of the system, changing reference temperature did not show a clear relationship with exergy efficiency. Finally, no clear relationship between energy and exergy efficiencies of the system was discovered; nevertheless, the higher the exergy efficiency of a system the lower the direct CO2 emissions from it.
Keywords: exergy analysis; thermodynamic systems; exergy indicators; district heating network; energy efficiency; CO2 emissions.
Comparative Energy and Exergy Analysis and Optimization Study on the Supercritical CO2 Recompression Power Cycle
by Emrah Gumus, Veysi Bashan
Abstract: The current study aims at optimization and comparing the recuperative s-CO2 cycle with the re-compression s-CO2 cycle in case of changes in turbine and compressor isentropic efficiency and TITs. Below 317 ? the TIT recuperated Brayton cycle (RBC) has a higher cycle efficiency than RCBC for the case where compressor efficiency is 75% and turbine efficiency is 80%. RBCs with having higher turbomachinery efficiencies (?c=85%, ?t=90%) have higher cycle thermal efficiency than RCBCs with lower turbomachinery efficiencies (?c=75%, ?t=80%). These results will remedy the gap in the literature on information for selecting the appropriate cycle for various purposes under certain thermodynamic inlet conditions.
Keywords: Recompression Cycle; Supercritical; s-CO2; Carbondioxide; Thermodynamic analysis; Exergy analysis.
Energy and Exergy Analysis of Transcritical CO2 Two Stage Compression Cycle
by Hongli Wang, Jingrui Tian, Yitai Ma
Abstract: Based on theoretical analysis and experimental testing, the performances of transcritical CO2 two stage compression cycle with two gas coolers were analyzed. The maximum experimental refrigeration COPc and heat COPh are 2.24 and 3.25, the maximum theoretical COPc and COPh are 2.85 and 3.85. The COP both of COPc and COPh decrease gradually with increasing of the outlet temperature of gas cooler, and the average value of experimental COPc and COPh are 2.02 and 3.13, the average value of theoretical COPc and COPh are 2.54 and 3.54. Range of the evaporating temperature from -5? to 17?, the average value of experimental COPc and COPh are 1.99 and 3.17. The exergy loss both of theoretical value and experimental value are all increase gradually with increasing of differential pressure of throttling valve. The error of exergy loss percentage on theoretical calculation and experimental testing are almost all within +20% and -20%.
Keywords: Transcritical CO2 two stage compression cycle; Theoretical analysis; Experimental testing; Energy analysis; Exergy loss.
Second-Law Thermodynamic Analysis on Premixed Syngas Flames
by Yusen Liu, Dong Han
Abstract: Exergy destructions in laminar premixed flames of syngas with varied fuel compositions, i.e. H2 and CO percentages, were numerically studied at both 1 atm and 5atm. Two syngas compositions, namely 30% H2/70% CO and 70% H2/30% CO, were selected for calculation. The processes causing exergy destructions were separated into heat conduction, mass diffusion and chemical reactions, and the chemical reactions were found the most dominant, followed by heat conduction and mass diffusion. With hydrogen enrichment, the proportion of total exergy destruction was increased by about 1%, but nearly unchanged with pressure elevation. Specifically, with hydrogen enrichment in syngas, the exergy destruction from heat conduction decreased mainly because the flame thickness was narrowed down, and that from mass diffusion increased as a result of high diffusivity of H2, H and H2O, whereas that from chemical reactions increased due to the higher reactivity of H2 than CO. In contrast, the pressure elevation had a more significant impact on the enhancement of exergy destruction rates and reduction of flame thickness. The higher temperature gradient and mole fraction gradients were dominant in the increased exergy destruction from heat conduction and mass diffusion, but the reduction of flame thickness resulted in that the exergy destruction from chemical reactions decreased.
Keywords: Second Law of Thermodynamics; Premixed flame; Syngas; Hydrogen.
Effect of biodiesel Blending with Diesel Fuel on CI Engine Performance and Energy Availability
by Jehad Yamin, Eiman Sheet
Abstract: Abstract. This paper discusses the effect of blending waste cooking oil biodiesel with diesel on the performance, emissions and engine availability of 4-stroke, direct injection diesel engine. This was done using both experimental and analytical methods. The software used was Diesel-RK. rnFirst, the engine was tested using locally available diesel in Jordan to set the baseline performance for comparison and then was run using other fuels and blends. rnFinally, the first and second law parameters were calculated and compared. It was found that 5-10% biodiesel blend gave an average of 5% improvement in the performance from power, torque, fuel consumption and thermal efficiency point of view. rnFurther, it was clear from second law analysis that biodiesel fuel and its blends higher than 10% failed to utilize the available energy of the fuel compared with diesel fuel.
Keywords: Second law analysis; engine availability; biodiesel fuel; diesel engine performance; exergy analysis; WCO Biodiesel; engine availability.
Performance evaluation of compressor assisted multi-effect absorption refrigeration cycles for power and cooling using evacuated tube collectors.
by Chinedu Frank Okwose, Muhammad Abid, Tahir Abdul Hussain Ratlamwala
Abstract: To improve the thermal energy utilization performance of an absorption cycle, compressor-assisted single, double and triple effect absorption refrigeration cycles for power and cooling are proposed in this study. Solar thermal energy from evacuated tube collectors is used as the heat source to drive the cycles. The power generated by the cycles is used to power the compression required to enhance the performance of the cycles. Based on the laws of thermodynamics, the effective energy efficiency and effective exergy efficiency were carried out to study the effect of the heat source temperature (ths,in) and the compression ratio (prcom) on the proposed cycles. In the base case of the proposed cycle (prcom=1.5), the simulation results show that the net power output decreased by 88%, while the cooling output increased slightly by 5.2% for the single effect cycle. The effective energy efficiency decreased from 14% to 13% and the effective exergy efficiency increased from 61% to 66% respectively. A further analysis of multi-effect cycles showed that the system can be operated at low temperatures, with the desorber temperature of double effect cycle decreasing by 32% while the desorber temperature for triple effect cycle decreases by 23% for a compression ratio of 1.5.
Keywords: Absorption refrigeration; compression ratio; power; multi-effect cooling; double-output; evacuated tube collector.
EXERGY ANALYSIS OF MICROCHANNEL HEAT EXCHANGERS
by Mehmed Rafet Özdemir
Abstract: This study investigates the exergetic efficiencies of plain microchannel heat exchangers under single-phase and two-phase operating conditions using de-ionized water as the working fluid. The friction factor and heat transfer coefficient data of microchannels are obtained using experimental studies from the literature and analytical/empirical correlations. The exergetic efficiencies of four plain microchannels are compared in order to reveal the effect of different geometrical parameters in terms of exergetic efficiency. The results showed that the microchannel aspect ratio (width/height) is an insignificant parameter on the exergetic efficiency for single-phase flow conditions. However, the exergetic efficiency increased with the decreasing of the microchannel aspect ratio in two-phase tests. On the other hand, the microchannel heat exchanger having shorter heated length exhibited better exergetic efficiency both in single-phase and two-phase regimes compared to the microchannel heat exchanger with longer heated length.
Keywords: microchannel heat exchanger; exergy analysis; single-phase flow; two-phase flow.
Exergy, exergoeconomic and exergy-based emission cost analyses of a coconut husk-fired power and desalination plant
by Atilio Lourenço, Monica Carvalho
Abstract: A renewable-based energy system is proposed herein, which employs coconut husk briquettes and produces electricity and fresh water for a small municipality. The energy system is constituted by a Rankine-based steam power plant and a set of mechanical vapor compression desalination modules. Exergy-based cost allocation methodology is applied to the system, where exergy, economic, and emission costs are allocated to both electricity and fresh water. Exergy analysis includes the cooling tower and ashes from the steam generator. It was verified that exergy destruction was the highest at the steam generator, and therefore parametric analyses were carried out to verify which parameters influenced its performance the most. From an economic viewpoint, the unit costs associated with electricity and fresh water were higher than the actual unit costs of the utilities available on site. From an environmental perspective, the emissions associated with the energy system were higher than those of average power plants (literature data). The energy system proposed herein could satisfy more than 70% of the water demand of the municipality. Despite technically and socially viable, there are still margins for improvement. Despite technically and socially viable, there are still margins for improvement.
Keywords: Exergy; exergoeconomics; coconut residue; biomass; desalination.
A New Perspective of Thermoeconomic Analysis on a Gas-steam Combined Cycle Power Plant
by Hongkun Li, Weidong Zheng, Jianhong Chen, Xiliang Hong, Xiaorong Wang, Qiangfeng Chen
Abstract: In this study, we have applied the H&S model to a gas-steam combined cycle power plant (CCPP) and further explore its advantages for thermoeconomic evaluation. First, we introduce how E&S model irrationally assesses the performance of both productive and dissipative components from the viewpoint of fuel-product model. Then, we build the thermoeconomic model of a typical gas-steam CCPP based on H&S theory and show the potential of improvement for each component. Specifically, we discuss in detail how the dissipative components can be assessed individually by H&S model. Thermoecomonic cost is divided into four parts (enthalpy cost, negentropy cost, dissipative cost and non-energy cost) to clearly understand how the cost accumulates in each component. Based on the relative cost difference and non-energy factor, we identify the causes for the main cost of the product in each component. For a CCPP, the results show that reducing non-energy cost of the steam turbine (ST) and the irreversibility of the combustion chamber (CC) can significantly lower the thermoeconomic cost of electrical power. For the condenser (CND) and stack (STA), the dissipative cost is responsible for the most of their thermoeconomic cost. It is concluded that thermoeconomic performance evaluation based H&S model gives a more reasonable result and can support the researches on thermoeconomic optimization.
Keywords: Thermoeconomic analysis; H&S model; combined cycle power plant; Performance evaluation; negentropy.
Time optimal control operation of bulk lyophilization of materials on trays reduces the exergy losses and increases the efficiency of energy utilization
by Athanasios Liapis, Roberto Bruttini, Jee-Ching Wang
Abstract: Exergy represents a measure of quality of energy and because exergy is destroyed due to process irreversibilities within a system to produce entropy, the exergy expressions and analysis presented in this work could be used to operate the intrinsically unsteady-state lyophilization processes more efficiently by decreasing the sources of existing inefficiencies in different parts of the freeze drying system. The expressions derived and presented for the calculation of the thermodynamic quantities of the exergy inputs and exergy losses due to heat and mass transfer in bulk freeze drying of materials on trays, show that the magnitude of these thermodynamic quantities are affected very substantially by the duration times of the primary and secondary drying stages of this intrinsically unsteady-state separation process. With the interest in mind to reduce the primary and secondary drying times, it is shown that the time optimal control operation of a freeze dryer with respect to heat input to the trays and total pressure in the drying chamber, reduces the duration times of the primary and secondary drying stages by 42.43% and 41.17%, respectively, and this leads to a reduction of 38.19% in the magnitude of the total exergy losses of the lyophilization system studied in this work. This reduction in the total exergy losses during the drying cycle time operation of a freeze dryer, implies that there is an increase in the efficiency of energy utilization under time optimal control operation. Also, the potential for reducing further the exergy losses when organic co-solvents and water forming non-ideal mixtures of solvents with positive deviations from Raoults law are used in a freeze drying system operated under time optimal control, is discussed
Keywords: Drying cycle time; Exergy inputs; Exergy losses; Freeze drying; Heat inputs; Lyophilization; Primary drying stage; Secondary drying stage; Time optimal control operation of freeze drying/lyophilization systems; Total pressure in vacuum chamber.
Economic and Exergetic Evaluation of Solar-Powered Combined LNG-Burned Micro gas Turbine and Stirling Engine
by Mojtaba Babaelahi, Hamed Jafari
Abstract: One of the important issues in the power generation is the selection of effective renewable energy powered system with the highest efficiency, lowest cost. In this paper, a new system for power generating based on micro gas turbine and Stirling engine using solar heliostat field is introduced. The proposed system uses the solar energy and combustion of LNG fuel as heat sources. Cost and exergy analysis has been used to achieve the evaluation of the proposed design. Therefore, in the first step, the energy and exergy analysis for the considered cycle has been performed. In the second step, the purchase cost of various components of the cycle is calculated and the corresponding cost equations are evaluated using the exergoeconomic balance equations. To calculate the purchase cost of different equipment, the detail design of the solar heliostat system, PCM storage tank, micro gas turbine, Stirling engine and LNG evaporator has been made. Then the sensitivity analysis of the design parameters has been evaluated on the efficiency and cost.
Keywords: Micro Gas Turbine; Stirling Engine; Solar; PCM; Exergy; Cost.
Energy and Exergy Analysis of the Heating and Cooling System of a Public Building
by Sezer Sevim, Ali Yurddas
Abstract: Efficient use of energy spent in existing systems is of great importance in terms of energy saving. The aim of this study was to carry out the energy and exergy analyzes of the existing heating and cooling systems of a public building and determine the system performances, and bring the system to a thermoeconomic structure by making necessary improvements. In the building, natural gas is used as energy source (fuel) in hot water boilers within the existing heating installation, and electricity is used as energy source in air-cooled water chillers within the cooling system. As a result of the calculations, it was determined that the biggest exergy destruction in the heating system was in the hot water boiler and the biggest exergy destruction in the cooling system was in the water chiller. Other point data obtained were evaluated and heating and cooling system efficiencies were determined.
Keywords: Energy Analysis; Exergy Analysis; HVAC; Efficiency; Building.
PERFORMANCE EVALUATION OF A-Si AND CdTe SOLAR PHOTOVOLTAIC USING ENERGY AND EXERGY ANALYSIS
by Mohammed Amine DERICHE
Abstract: In the paper, analysis and a comparative study of exergetic performance has been made for amorphous silicon and cadmium telluride solar PV array in Oued Nechou at Ghardaia, Algeria (32
Keywords: Photovoltaic; energy; exergy; efficiency; temperature; solar radiation; wind speed; comparative study.
ADVANCED EXERGY ANALYSIS OF A JET EJECTOR REFRIGERATION CYCLE USED TO COOL DOWN THE INTAKE AIR IN AN INTERNAL COMBUSTION ENGINE
by Jose Galindo, Vicente Dolz, Benjamin Pla, Alberto Ponce-Mora
Abstract: This paper describes a jet ejection cycle coupled to a 1.5l Diesel engine to reduce the intake air temperature using the waste heat of the exhaust gases. This cycle is evaluated by means of conventional and advanced exergy analysis. The conventional analysis allows to determine the origin and magnitude of the irreversibilities, whereas the advanced analysis sheds light on the mutual interdependencies between components and the real improvement potential considering technological limitations. From the conventional exergy analysis it is inferred that more than a half of exergy destruction is due to generator followed by ejector (one-third part) and condenser. However, the advanced exergy analysis suggests that the ejector plays a prominent role because the avoidable endogenous part corresponds to 42% of total exergy destruction in that component whereas the avoidable part of exergy destruction in the generator is mostly exogenous (83%). Hence, exergy destruction could be significantly reduced if improvement efforts are focused on the ejector instead of other components like the generator.
Keywords: Waste heat recovery; jet ejector refrigeration cycle; internal combustion engine; performance optimization; genetic algorithm; simple exergy analysis; advanced exergy analysis.
The investigation of exergoeconomic, sustainability and environmental analyses in an SI engine fuelled with different ethanol-gasoline blends
by Battal Dogan, Dervis Erol, Evren Kodanli
Abstract: In this study, performance and emission values were obtained under full load by using ethanol-gasoline blends as fuel at different rates in a spark-ignition engine, and exergy, exergoeconomic and exergoenvironmental analyses were performed with these values. Exergy of fuel entering engine and lost exergies through cooling system, exhaust and radiation were calculated. CO, CO2, HC, and NOX emissions released from engine into environment were measured, and according to exergoenvironment analysis, cost of CO2 emission was calculated as 393.78 USD/year for E0 fuel and as 306.78 USD/year for E30 fuel at 2000 rpm. Ethanol-gasoline blends at different rates, environmental damage can be reduced by around 30% on an annual basis. Furthermore, with exergoenviroeconomic analysis, lowest engine output power cost was found to be 29.77 USD/MJ in E0 fuel at 2000 rpm, while highest engine output power cost was found to be 120 USD/MJ in E30 fuel at 4500 rpm.
Keywords: spark-ignition engine; ethanol; exergy; exergoenviroeconomic; exergoenvironment; sustainability index;.
Advanced exergoeconomic analysis of solar-biomass hybrid systems for multi-energy generation
by ALAIN BIBOUM, Ahmet YILANCI
Abstract: In this study, advanced exergoeconomic analysis of solar-biomass hybrid energy systems for the northern part of Cameroon is conducted. Three concentrating solar power (CSP) technologies, Parabolic Trough Collector (PTC), Linear Fresnel Reflector (LFR) and Solar Tower (ST), hybridized with biomass-fired (BF) technology are investigated. It is found that exergy destruction from the solar field alone is responsible for the most of the whole exergy destructions (86.3% for PTC-BF, 92.2% for ST-BF and 85.4% for LFR-BF). The results show that LFR-BF hybrid system is the best cost-efficient system while ST-BF hybrid system is the worst cost-efficient system considering initial investment, avoidable-endogenous exergy destruction, cost associated with avoidable-endogenous exergy destruction and total cost required for the optimization.
Keywords: hybrid system; advanced exergy analysis; advanced exergoeconomic analysis; solar thermal power; concentrating solar energy; biomass.
Entropy Generation and Heat Transfer in Magnetohydrodynamic Two-Dimensional Stagnation-point Flow on a Sliding Plate
by Mehmet Demir
Abstract: Entropy generation and heat transfer in magnetohydrodynamic two-dimensional stagnation point flow of a viscous fluid over a moving horizontal plate have been investigated. The temperature of the plate is constant and sliding with a constant velocity in its own plane. An alternative similarity transformation has been proposed for the temperature field for not to neglect the viscous dissipation and Ohmic heating terms in the energy equation. The governing equations are reduced to a set of non-linear ordinary differential equations by using appropriate similarity transformations. Velocity components, temperature field, and local entropy generation rate are obtained numerically by using the Matlab built-in routine bvp4c. A new dimensionless group is used to represent the magnitude of dissipation which allows the transition to some special cases. The effects of the dimensionless parameters on the velocity components, temperature, and entropy generation are carefully examined and presented graphically. It has been observed that when the magnitude of the dissipation is high then an increase in the external magnetic field causes the increment of the temperature and entropy generation while decrementing the heat transfer from the wall to the fluid. In the other case, the effect of the external magnetic field is the opposite on the temperature and the heat transfer. Also, it has been shown that to neglect the viscous dissipation and/or Ohmic heating terms in the energy equation may lead to errors.
Keywords: Similarity transformation; Entropy generation; Stagnation point flow; Magnetohydrodynamics (MHD).
Sugarcane bagasse and vinasse conversion to electricity and biofuels: an exergoeconomic and environmental assessment
by Rafael Nogueira Nakashima, Daniel Flórez-Orrego, Hector Ivan Velásquez, Silvio De Oliveira Junior
Abstract: Biomass conversion into either electricity or biofuels requires various energy intensive processes that may drastically affect its technical and environmental competitiveness against their non-renewable counterparts. Therefore, in this paper, a comparative assessment between the total (c_t) and non-renewable (c_nr) unit exergy costs and specific CO_2 emissions (c_co2) of the electricity, methane and hydrogen produced from sugarcane vinasse and bagasse is presented and compared with the conventional (fossil fuel-based) supply chains. As a result, the non-renewable unit exergy costs and specific CO_2 2 emissions for the transportation service in all cases analyzed are 3.1 to 4.7 times lower compared with conventional fossil fuels (e.g. diesel, gasoline, natural gas and hydrogen). Among the waste upgrade alternatives, methane production is able to maximize the exergy flow rate of products in the transformation stage (52.4-58.6 MW), while hydrogen and electricity production can substantially increase the transportation service in the end-use stage (51.7-52.1%) and the operational revenues (2706-2889 EUR/h).
Keywords: sugarcane bagasse; vinasse; ethanol; biofuels; electricity;exergoeconomy; waste upgrade; environmental assessment; greenhouse gas emissions; biorefinery; anaerobic digestion; biomass gasification; hydrogen; biomethane; synthetic natural gas.
Exergoenvironmental Analysis and Evaluation of Coupling MSF, MED and RO Desalination Plants with a Combined Cycle Plant
by Mohammad Hasan Khoshgoftar Manesh, S. Kabiri, M. Yazdi
Abstract: In this paper, freshwater production through Multi-Effect Desalination (MED), Multi-stage Flash (MSF), Reverse Osmosis (RO), hybrid (MED+ RO) and hybrid (MSF+ RO) units have been investigated in view of Exergetic, Economic, and environmental analysis. Results show that the maximum amount of freshwater produced occurs in the combined cycle coupling with the MSF unit. This cycle can produce 1056.67 cubic meters per hour of freshwater. The amount of electricity power consumed in RO desalination unit is the lowest specific energy consumption among all desalination methods. The unit consumes about 5 kWh of electricity per cubic meter of freshwater produced. The cost of producing freshwater per RO desalination unit is very low. The RO unit freshwater price is about $ 0.1 per cubic meter. The integration of the selected desalination plants with Qom combined cycle power plant, the pollutants from the fuel and product of each equipment has been decreased significantly. Thus, the combined cycle combined with the MED unit the environmental impact rate decreased by 23% compared to the combined cycle. Also, in the integration of combined cycle with MSF unit, RO unit, MED_RO unit, and MSF_RO unit, it has been found that 25%, 60%, 27%, and 25% decrease can be obtained in the environmental impact rates, respectively.
Keywords: multi-stage flash desalination; Reverse Osmosis; multi-effect desalination; exergy; exergoenvironmental analysis; combined cycle power plant.
Comparative performance of an automobile heat pump system with an internal heat exchanger using R1234yf and R134a
by Erkutay Tasdemirci, Murat Hosoz
Abstract: Automotive heat pump (AHP) systems have been using in vehicles where waste heat is limited such as electric cars. Due to its impact on global warming, the use of R134a was restricted, and R1234yf has been regarded as its best alternative for automotive air conditioning systems. The AHP systems using R1234yf perform poorly, and a remedy to this problem may be the use of an internal heat exchanger (IHX). This study aims at evaluating and comparing various performance parameters of an experimental AHP system using R134a and R1234yf with and without an IHX. The findings revealed that the R1234yf system with IHX provided only 13.9% lower heating capacity but 7.8% higher COP based on total power consumption in comparison to the R134a system. Moreover, for 5
Keywords: R134a; R1234yf; heat pump; automotive; air conditioning.
A More Realistic Performance Evaluation of Solar Convertors: The Need for Exergic Spectral Analysis of Radiative Heat Transfer
by Amir Arya, Mahmood Yaghoubi, Khosrow Jafarpur
Abstract: Solar energy harvesting devices have got considerable attention by researchers and significant efforts have been made to optimize their performance recently. For efficiency studies, exergy analysis is a useful approach to evaluate the thermodynamic behavior of the related system. However, in contrary to conduction and convection mechanisms, the exergy theory of radiation is not well developed, yet. The conventional theory of Petela for radiation exergy, despite its global usage is not well applied for solar energy convertors which are working in a certain spectrum bandwidth such as photovoltaic (PV) panels. More specifically, the inlet exergy of PVs are generally assumed to be the full spectrum exergy, which is not the case for the available panels and consequently the calculated efficiency is underestimated. In the present study, the energy and entropy fraction functions are presented as a function of wavelength and temperature. Then, the integral form of the radiation exergy in a specified wavelength bandwidth is derived as a function of dimensionless wavelength and temperature. It is shown that in contrary to energy and entropy, the exergy fraction function cant be expressed as a function of a single variable (i.e. ?T). As an application, the second law efficiency of various PV panel types are estimated based on the proposed method and compared with those predicted by the usual approach. It is shown that up to 55 % error for exergic efficiency of PV panels might occur by using the conventional relation.
Keywords: Radiation exergy; Photovoltaic energy; Spectral performance; Petela’s formula; solar energy; radiation entropy; Black body fractional function;.
Exergy Analysis of Crude Oil Gathering and Transportation System by Three Box Model
by Qinglin Cheng
Abstract: "Three box" exergy analysis optimization method is applied to oil field system in order to identify and improve the weak links of crude oil gathering and transportation system. The universal Black Box, White Box, Gray Box models and balance equations of oil field analysis are established according to different requirements of rough, fine and sub-fine analysis. The weak link of energy utilization is determined. The heating furnace is identified as the lowest exergy efficiency equipment in crude oil gathering and transportation system, which can provide a theoretical basis and scientific method for improving system energy efficiency.
Keywords: "Three box" model; crude oil gathering and transportation system; weak link of energy utilization; heating furnace.
Performance Assessment of a Modified Power Generating Cycle based on Effective Ecological Power Density and Performance Coefficient
by GÜVEN GONCA, Bahri Sahin, Mehmet Cakir
Abstract: Thermo-ecological performance optimization and analyses of an engine running with a modified power generating cycle are carried out based on Effective Ecological Power Density (EFECPOD) and Effective Ecological Performance Coefficient (EFECPEC). They provide a unique value for combined characteristics of thermal efficiency, power, cycle volume, entropy generation and maximum combustion temperature. The impacts of design and operational parameters such as compression ratio, equivalence ratio, engine speed, exhaust temperature ratio, pressure ratio, cycle pressure ratio and cycle temperature ratio on maximum EFECPOD and EFECPEC have been examined for modified power generating cycle.
Keywords: Internal combustion engine cycles; Performance characteristics; EFECPOD; Thermo-ecology.
First and Second Law Based Thermal Optimisation of the Kalina Cycle Integrated into an Existing Burner-Based Cogeneration System Using Waste Chips as Fuel
by Yildiz Koc, Huseyin Yagli
Abstract: Due to increasing energy demand and decreasing fossil resources, the optimisation of existing systems has a critical role to minimise energy consumption and diminish the adverse effect of power systems on the environment. Therefore, the main interest of researchers is mainly focused on developing a new combined system to use energy sources more efficient. In the present study, a KC was integrated into an existing burner, which uses waste chips as fuel for producing steam and drying moist fiber. The KC was analysed based on the first and second law of thermodynamics and thermally optimised. After detailed analyses for varying turbine inlet temperature at 50 bar (up to 330
Keywords: Exergy; Kalina cycle; performance analysis; thermal optimisation; waste heat recovery; wood chipboard production.
An Exergy Study on Compression Ignition Engine Operating with Biogas Gas and Coke Oven Gas
by Hongqing Feng, Zhirong Nan
Abstract: This paper studies the combustion emission characteristics, exergy conversion and utilization, and irreversibility of compression ignition (CI) engines fueled by coke oven gas (COG) and biogas, which is conducted by establishing a zero-dimensional single-zone combustion model and an exergy analysis model. When the intake air temperature is same, the peak temperature of the COG in the cylinder is higher than the biogas, and the difference is about 64K, which results in much higher NOx emission of the coke oven gas. The irreversible loss of COG-fueled engines in the working process is 22% and the working exergy accounts for 58%, which is much larger than biogas. By properly increasing the intake air temperature, the intake pressure and speed can reduce the irreversible loss.
Keywords: Coke oven gas; Biogas; Exergy analysis; Compression ignition engine.
Exergy analysis of a shell & tube heat exchanger using DETHE software
by Joaquin Zueco, Sergio Ayala-MiÃ±ano
Abstract: In this paper, a sensibility study of irreversibility due to geometrical parameters variation of a shell-and-tube heat exchanger is proposed by using an exergy analysis. The irreversibility calculation model has been implemented on DETHE (Design Tubular Heat Exchangers) software, where thermohydraulic calculations are based on Bell-Delaware method. A prior evaluation of thermohydraulic results of DETHE is provided against a commercial software. Through an exergetic analysis in the study case, formulation to be implemented in the software for irreversibility calculation is developed. A real case study of a heat exchanger located in a pre-heat train of atmospheric crude distillation unit is analysed. Irreversibility results due to key design parameters variation for this heat exchanger are provided and discussed.
Keywords: Heat exchanger; Exergy method; Irreversibility; DETHE; Bell-Delaware; Second Law Thermodynamics.
Exergy analysis of plate heat exchanger with graphene alumina hybrid nanofluid: Experimentation
by Atul Bhattad
Abstract: The water-based hybrid nanofluid is proposed as a cooling agent in a corrugated counter-flow type plate heat exchanger aimed at sub-ambient temperature applications. For this purpose, an experimental investigation has been done with different working fluids. Fluids considered as a coolant are DI water, alumina nanofluid, and alumina-graphene hybrid nanofluid in 80:20 nanoparticle ratio by volume with a total volume concentration of 0.01% dispersed in DI water. Various exergy related performance factors like coolant outlet temperature, coolant exergy rate, irreversibility rate, non-dimensional exergy, and second law efficiency have been considered. The influence of coolant inlet temperature and flow rate on different parameters has been investigated. Coolant outlet temperature, coolant exergy rate, irreversibility rate and non-dimensional exergy augments by 2.5%, 4.8%, 7.5% and 3.5%, respectively. While the second law efficiency degrades using nanoparticles and increasing flow rate and decreases with the coolant inlet temperature.
Keywords: Hybrid nanofluid; Plate heat exchanger; Graphene; Non-dimensional exergy; Irreversibility; Second law efficiency.
Energetic and exergetic analysis of a novel geothermal driven multi-generation system using n-pentane as working fluid
by Nima Khosravi, Devrim Aydin
Abstract: In the present study, a geothermal driven multi-generation system for electric power, heating, cooling and hydrogen production is introduced. The proposed system is based on an Organic Rankine Cycle (ORC), where n-pentane is used as the working fluid. Within the study, it is aimed to evaluate the impact of geothermal source flow rate/temperature, ambient temperature and turbine inlet pressure on the energetic and exergetic performance of different system components. Besides, the overall first and second law efficiencies of the multi-generation system for different operating conditions are determined.
In the investigated system, generated electricity can be partially used for domestic needs while the rest is proposed to be used for hydrogen production through an electrolysis process. Heat recovered from the ORC is also utilized for driving a single-effect absorption chiller (SEAC) for producing heating and cooling. The study results showed that the optimum mass flow rate and temperature of the geothermal source are 11.88 kg/s and 483.2 K, respectively. For the optimized operating conditions of the proposed multi-generation system, overall energetic and exergetic efficiencies were determined as 0.56 and 0.41, respectively.
Keywords: multi-generation system; exergetic assessment; geothermal energy; organic rankine cycle; power generation; heating and cooling; electrolysis; hydrogen production; n-pentane; absorption.
Evaluation of an Urban Area in Cold Climate with a New Perspective: Exergoeconomic Analysis
by Yelda MERT, Suha Orçun MERT
Abstract: The Exergoeconomic analysis of an urban area is introduced in this study, performed in an annual energy interaction basis. The investigated period covers the year of 2016, and indoor and outdoor temperatures, construction properties, and annual energy consumptions for heating purposes were all taken into account during the analysis. The selected urban area is the Campus housings of Van Yuzuncu Y?l University, which were constructed in 2012 after the Van Earthquakes. Known as an important tool in understanding the cost structure of energy-intensive sectors, the exergoeconomic analysis was introduced as part of the planning concept in the study, and the analysis involves the results of exergetic cost and exergy efficiency analyses for the case area. Considering the urban nature of the study location, annual meteorological and domestic values were fully covered in the calculations. The results show that, despite being a well-designed and constructed urban area, certain specific design considerations were not met, and there is plenty of space for improvement in cost-reduction, particularly so for a location with such a cold climate.
Keywords: efficiency; exergoeconomy; exergy; mass housing; urban area planning.
Energy and exergy analyses of solar drying sardine fillets
by Hamza Lamsyehe, Younes Bahammou, Hind Mouhanni, Mounir Kouhila, Zakaria Tagnamas, Haytem Moussaoui, Abdelkader Lamharrar, Ali Idlimam
Abstract: Fish is a highly perishable food product. It has a very short because it contains up to 78% of water. The aim of this work is to examine the effect of solar drying on the dehydration kinetics of Moroccan sardine fillets. The curves of the experimental kinetics of drying sardine fillets are carried out at four temperatures (50, 60, 70 and 80
Keywords: Activation energy; diffusion coefficient; exergy; sardine fillets; solar drying.
Optimized Annual Performance of Hybrid Solar Energy MED-TVC Desalination Plants with and without Preheating
by Davood Beyralvand, Mahmood Yaghoubi
Abstract: In the current study, energy, exergy, economic and environmental (4E) analysis for a multi-effect desalination plant with and without feed brine preheater integrated with a steam boiler and solar hybrid system for three coastal cities of southern Iran during a year is investigated. Four main configurations of hybrid/MED-TVC, hybrid/MED-TVC.FH, boiler/ MED-TVC and boiler/MED-TVC.FH are considered. By using Artificial Bee Colony algorithm, systems were optimised. The results show that: using feed brine preheater, the unit cost reduced by 6.5% for the system with a boiler and 3.8% for the hybrid system.
Keywords: Solar energy; MED-TVC.FH; CO2 emission; ABC algorithm; 4E analysis.
Parametric analysis of Energy and Exergy of the human body in Indian conditions
by Arvind Kumar Patel, SATISH P.A.L. SINGH Rajput
Abstract: The second law of thermodynamics is useful to examine the energy and exergy analyses of any energy conversion system. Over the past decades, this law is also applied to biological systems, such as the human body and other natural species. In this work, energy and exergy parameters of the homeotherms in the summer and winter seasons are performed for Indian conditions by using the approach of exergy analysis. For this study, Bhopal (India) is selected as the location for environmental data. The weather of Bhopal is hot and arid for summer and cold and dry for the winter. The outcome of this work indicates that the energetic metabolic rate is much higher than the metabolic exergetic rate. The actual metabolic rate for the summer season is 60 W/m2 compared to 72.91 W/m2for the winter and the metabolic exergetic rate for winter is almost three times higher than summer. The maximum energy loss from all sources of heat transfer is calculated as 34.26 W/m2 in summer and 40.48 W/m2 in winter.rnFurther in the summer season, the Predicted Mean Vote value is 0.85, and in winter, this value is slightly higher at1.06. Because of the higher Predicted mean vote value, the Predicted Percentage Dissatisfaction is also somewhat high. The Predicted percentage of dissatisfaction values for summer and winter are 24.49% and 28.71%, respectively. These results indicate that thermal dissatisfaction is more significant in the winter season compared to the summer season. rn
Keywords: Energy; Exergy; PMV; PPD; Thermal Comfort; Summer; Winter.
Application of Cumulative Exergy Consumption Approach to Assess the Sustainability of Rapeseed Production in Two Different Farming Systems
by Mahdi Esmaeilpour-Troujeni, Abbas Rohani, Mehdi Khojastehpour
Abstract: The study aimed to assess the sustainability of mechanized production system (MPS) and semi-mechanized production system (SMPS) in the rapeseed agroecosystem in northern Iran. The study was conducted through the cumulative exergy consumption (CExC) approach, including the two sustainability indices of cumulative degree of perfection (CDP) and renewability index (RI). The CDP was higher in the MPS (4.36) than SMPS (4.29). The RI was determined to be 0.712 for MPS and 0.731 for SMPS. The results highlighted that CDP and RI could significantly be improved through the consumption of renewable-based energy resources, including biofuel and solar energy.
Keywords: Cumulative exergy consumption; Mechanized and Semi-mechanized; Rapeseed; Renewable energy; Sustainable agriculture.
Energy, Exergy and Exergo-environmental Assessment of a Novel Solar powered Kalina Cycle Incorporated with Micro-CCHP for Poly-generation.
by Victor Adebayo, Michael Adedeji, Muhammad Abid, Olusola Bamisile
Abstract: In this study, a solar parabolic trough collector combined with a Kalina cycle, multi-stage flash desalination unit, a proton exchange membrane electrolyzer for hydrogen production, and a micro-combined cooling, heating, and power system is presented. Systematic energy, exergy, and exergo-environmental evaluation is used to analyze the viability of the integrated systems as the most effective approach for performance assessment of integrated systems. The energy and exergy efficiencies of the overall system is observed to be 50.51% and 3.27% respectively. The rate of exergy destruction of each component and the overall cycle is determined where the parabolic trough collector is shown to have an exergy destruction rate of 234.4kW, which is the highest among all the components. The performance of the proposed systems is also checked through a parametric study of the different key parameters.
Keywords: Energy; Exergy; Exergo-environmental; Desalination; Hydrogen.
Enhanced exergy based malfunction diagnosis of an integrated solar combined cycle system: Parametric study and multi-objective optimization
by Fateme Ahmadi Boyaghchi
Abstract: In this research, a malfunction diagnosis method based on the enhanced exergy concept is applied to quantify the anomalies' sources in a real integrated solar combined cycle system (ISCCS). A comprehensive parametric study is performed to evaluate the malfunction indicators and the overall performance of the power plant by varying the substantial operating parameters under single and multi-malfunction conditions. Then, the fast and elitist non-dominated sorting genetic algorithm (NSGA-II) is applied to maximize the net power and minimize the total exergy destruction rate of the system under a multi-malfunction condition.
Keywords: Malfunction diagnosis; performance degradation; enhanced exergy; ISCCS; parametric study; optimization.
Environmental life cycle assessment of an ammonia production process through Cumulative Exergy Demand and ReCiPe: A focus on power generation from natural gas and biomass
by A. Ghannadzadeh, R. Shabani, H. Ale Ebrahim
Abstract: The environmental impacts of the ammonia production process are because of the discharge of harmful chemicals as well as the high electricity demand. One way to control its environmental impacts in the electricity transition phase, is the natural gas/biomass based scenarios. This Life Cycle Assessment (LCA) study, which has used ReCiPe and Cumulative Exergy Demand, proves that natural gas is not right option for this specific case because the natural gas-based scenarios have more burdens than the residual fuel oil-based scenarios especially regarding Fossil Depletion (0.72%), Human Toxicity (14%), Freshwater Ecotoxicity (23%), Particulate Matter Formation (33%), Marine Ecotoxicity (37%), and Terrestrial Acidification (40%). Moreover, this study shows that it is possible to reduce the environmental impacts without retrofitting the heart of process technology using the biomass-based scenarios. This paves the way for a sustainable ammonia process under the energy transition scenarios where retrofitting the process heart is not desired.
Keywords: Environmental sustainability; Exergy; ReCiPe; Energy transition; Bioenergy; Monte Carlo simulation.
Special Issue on: GCGW-2019 Exergy Analysis of Processes Associated with Global Warming
ASSESSMENT AND APPLY OF AN ENHANCED EXERGY ANALYSIS FOR AN ARGON LIQUEFACTION SYSTEM
by Arif Karabuga
Abstract: Argon is one of the three basic elements in the air and is obtained by separating the air. It can be stored in liquid form using different liquefaction methods. Its basically and widely liquefied by three different liquefaction methods such as cryogenic, pressure swing adsorption and membrane. The main difference between these three methods is that the purity rates of the products obtained are different. The cryogenic method with the highest purity rate constitutes the method of this study. In the present work, conventional and enhanced exergy analyses were applied to the liquefaction process of argon gas. In the conventional exergy analysis, only the exergy efficiency and exergy destruction rate of the components are calculated. For the process improvement, more detail data about the origin of the destructions and effect of the components mutual on the exergy destructions would be required. In the enhanced exergy analysis, splitting the exergy destruction into endogenous/exogenous and avoidable/unavoidable parts represents a new direction. In the study, forward exergy analysis is performed for each component and endogenous, exogenous, unavoidable and avoidable values of these components were calculated. When the convectional exergy analysis is examined, the exergy efficiency of the argon gas liquefaction system is calculated as 51.77 %. When the enhanced exergy analysis of the system is examined, it is found that the highest exergy destruction occurred in the turbine as 614.3 kW. Furthermore, the highest endogenous exergy degradation was found as 494 kW (%80.4) in the turbine.
Keywords: Enhanced exergy analysis; Liquefaction system; Argon; Cryogenic; Exergy.
Special Issue on: ECOS 2019 Progress in Exergy Analysis of Energy Systems
Exergy Analysis of Novel Integrated Systems Based on MHD Generators
by Hossein Sheykhlou, Samad Jafarmadar, Rogayieh Abbasgholi Rezaei
Abstract: The present work concerns with the thermodynamic analysis of novel opened and closed Magneto Hydrodynamic Organic Rankine Cycles (MHD-ORCs). In this regard, the thermodynamic simulation of the integrated systems with the assumption of the constant stream velocity in the MHD generator has been performed. The impact of MHD input temperature, the electrode surface area, the plasma velocity, and the compressor isentropic efficiency on the overall performance of the combined cycles have been investigated. Moreover, exergy and thermal efficiencies of opened and closed MHD based cycles have been calculated and achieved in optimal points as follows; 66.15 %, 71.67%, 49.21 %, and 39.77%, respectively.
Keywords: Magneto Hydrodynamic Organic Rankine cycle; MHD generator; Coal combustion; Exergy Efficiency; Thermal Efficiency.