Exergy Production Research Articles

Quantity and Quality of Dual Fuel IC Marine Engine Exhaust Sensible Waste Heat Considering Different Sulphur Content in Fuels

Maritime transport is facing a significant set of technical challenges due to planned by the International Maritime Organization implementation of ecological criterions on 01 January 2020 and 2021 regarding the emission of sulphur oxides, carbon dioxide and nitrogen oxides. The advantageous properties of natural gas (NG) as fuel in conjunction with dual fuel (DF) internal combustion (IC) engines potentially enables the fulfilment of all planned criterions. However, if the methane emission of DF IC is taken into consideration in CO2 emission balance it completely devaluates the advantages arising from high hydrogen to carbon ratio of NG. On the other hand, the planned global sulphur cap in combination with its low content in NG potentially enables to recover higher rates of waste heat and exergy of combustion products without the risk of low temperature corrosion (compared to liquid fuel). In this study the influence of sulphur content in NG and pilot fuel on the sulphuric acid condensation temperature was investigated in order to determine the rate of waste heat (quantity) and exergy (quality) of four stroke DF IC engine combustion products. In ideal process scenario (exergy based) the methane slip effect compensation was achieved only for a 0,5 engine load.

Daily performance of a solar dish collector

Solar energy exploitation is one of the most promising techniques for achieving the sustainability in the energy domain. The objective of this work is to investigate the daily performance of a solar dish collector under different operating temperature levels. A solar dish collector with 10.28 m2 aperture and a spiral coil absorber is investigated. The analysis is performed with a developed numerical model in engineering equation solver which has been validated with experimental results. The analysis proved that the daily thermal efficiency of the collector is ranged from 67.36% to 54.65% for inlet temperatures from 50?C to 350?C, respectively. On the other hand, the exergy efficiency presents an increasing rate of the inlet tem?perature and it is found to be ranged from 8.77% up to 31.07% for the respective temperatures. The daily exergy production of the collector can reach up to 26 kWh with a respective thermal production of 50 kWh for inlet temperature equal to 350?C. The results of this work can be exploited for the suitable evaluation of the solar dish collector on a daily basis.

Experimental and theoretical performance evaluation of evacuated tube collectors under mediterranean climate conditions

In this study four evacuated tube collectors with cylindrical absorber connected in series are investigated experimentally and mathematically under the climatic conditions of Greece. The main objective of this study is to evaluate the collectors’ performance in terms of thermal energy and exergy production. The developed model regards the optical efficiency and thermal losses for the determination of both first and second law efficiencies and it is validated against experimental data with an acceptable agreement being observed. In specific, the average absolute deviation of the model from the experimental data is 1.46% and 8.55% for outlet temperature and useful thermal output, respectively. After the model validation, the performance of the collectors is analyzed in terms of thermal and exergy efficiency and thermal losses for various parameters including the mass flow rate, the inlet temperature, the available irradiance and the ambient temperature. A sensitivity analysis is conducted so as to determine the parameter that influences the most the overall performance of the investigated collectors. The final experimental results proved that these solar collectors connected in series work efficiently throughout the experimental process with a peak production of 5.6 kW. Among the main findings, the inlet temperature is the variable that affects the most both first and second low efficiencies.

Exergetic ecological index as a new exergetic indicator and an application for the heat engines

Aim of this paper is to present a new exergetic index. This index is called exergetic ecological index and it is adopted from the ecological function that provides opportunity to compare power output (desired output) and exergy destruction (lost power). The bigger ecological function means the more efficient and environmental friendly energy system. However, this criterion does not give any information about relation with the exergy source and exergetic ecological index provides this comparison. Finally, exergetic ecological function includes product exergy, exergy destruction and exergy source in a one equation and enables to evaluate any energy system considering with these three parameter.

Configuration optimization of an enhanced ejector heat exchanger based on an ejector refrigerator and a plate heat exchanger

Ejector heat exchanger has good performance in heat transfer, but its regulating characteristics are poor, and to improve its regulating characteristics, an enhanced ejector heat exchanger (EHE) with a pressure booster is presented. According to the difference in location of the pressure booster, the enhanced ejector heat exchangers are divided into two types. One is EHE-MF with its pressure booster located in the pipeline between outlet of ejector and refrigerant inlet of the condenser. The other is EHE-SF with its pressure booster located in the pipeline between secondary fluid inlet of ejector and refrigerant outlet of the evaporator. The two enhanced ejector heat exchangers have been analyzed from the perspective of thermodynamics. The results show that the location of pressure booster in the pipeline between outlet of ejector and refrigerant inlet of the condenser contributes to decreasing boosted pressure and power and increasing product exergy efficiency. The EHE-MF has higher thermodynamic performance, and its system configuration is optimal from the perspective of thermodynamics.

Thermo-economic analysis and comparative study of transcritical power cycles using CO2-based mixtures as working fluids

Transcritical carbon dioxide (CO2) cycle is a promising method to utilize both low and high temperature heat sources. However, its application is restricted to lower temperature cooling source conditions since the condensing temperature must be lower than the critical temperature of CO2 (about 31.1 °C). In this study, organic fluids are selected to blend with CO2 to overcome the condensation problem by elevating the critical temperature. The effects of several key parameters on thermodynamic and exergoeconomic performances of the system are investigated for different CO2-based mixtures and pure CO2 under both low and high temperature heat source conditions. Single-objective and multi-objective optimizations are carried out to achieve the better system performances. Meanwhile, the performance comparisons between different CO2-based mixtures and pure CO2 are conducted. Results show that transcritical power cycle using CO2-based mixtures could obtain better thermodynamic and exergoeconomic performances compared with the one using pure CO2 for both low and high temperature heat source conversions. Among the CO2-based mixtures and pure CO2, CO2/R32 presents the highest exergy efficiency of 52.85% and CO2/R161 presents the lowest levelized cost per unit of exergy product of 47.909$/MWh for low temperature transcritical power cycle. For high temperature transcritical power cycle, CO2/Propane presents the lower levelized cost per unit of exergy product of 29.212$/MWh.

Presentation of two new two-stage desiccant cooling cycles based on heat recovery and evaluation of performance based on energy and exergy analysis

In recent years the importance of the issue of energy saving in air conditioning industry, has been taken into more consideration. Using natural refrigerants and setting up a system which is driven by low grade thermal energy sources such as solar energy are the reasons why desiccant cooling systems are alternatives to conventional vapor compression cooling systems. Due to the increase in capacity of dehumidification and decrease in required regeneration temperature in two-stage desiccant cooling systems, they are more efficient than one-stage systems. In addition, heat recovery in a two-stage cycle leads to a reduction in energy consumption. In this paper two new two-stage desiccant cooling cycles which work based on heat recovery are presented. The studied cycles according to their process air are classified into fresh air and returned air cycles. In order to assess the performance of presenting cycles and compare them with the conventional one-stage cycles, energy and exergy analysis are performed. In exergy analysis, some equations are redefined. Furthermore, the amount of fuel exergy, product exergy, summation of exergy destruction and exergy loss and exergy efficiency for each component and the overall system are calculated in all cycles which are studied in this paper. For the regeneration temperature equal to 80 °C, using the presented two-stage fresh air cycle, decrease temperature and enthalpy of the supplied air 13.06% and 13.76% respectively. Moreover increases the coefficient of performance and exergy efficiency 37.66% and 1.12% respectively compared to conventional one-stage fresh air cycle. In addition using the presented two-stage returned air cycle leads to 12.56% and 12.77% reduction in temperature and enthalpy of the supplied air and it increases coefficient of performance and exergy efficiency 6.87% and 0.49% respectively compared to the conventional one-stage returned air cycle.

EXERGO-ECONOMIC ANALYSIS OF MICROCHANNELS IN SINGLE-PHASE FLOW

With the increase of energy demand, many researchers tried to develop scientific approaches in order to design more efficient and environmentally friendly energy systems. Exergo-economic (thermoeconomic) analysis of a system or device is an efficient tool for evaluating the system in terms of the thermodynamic and economic aspects. In this parametric study, exergo-economic analysis of rectangular copper plain microchannels under single-phase flow conditions were investigated using de-ionised water. The exergo-economic performance was evaluated based on the relative cost difference and unit cost per product exergy tools. The channel aspect ratio effect on the unit cost per product exergy and relative cost difference was examined using three microchannel test sections with the same channel hydraulic diameter (Dh = 0.56 mm) and length (L = 62 mm) but different aspect ratios (β = 0.5, 2.56 and 4.94) under single-phase flow conditions. The results showed that the exergo-economic performances of the three microchannel test sections decreased as the net heat input increased over the experimental range. Moreover, the exergo-economic performance of test section 2 (β = 4.94) was found to be greater than the exergo-economic performances of test sections 1 and 3 (β = 0.5 and 2.56) at fixed flow rate and fixed net heat input case.

Integrated Biomass Gasification Combined Cycle Plant for Small Scale Generation: Part B- Exergetic and Exergo-economic Analyses

This part of the paper deals with the exergetic and exergo-economic analyses of a small scale biomass integrated gasification combined cycle (BIGCC) plant. Basic configuration and operational parameters are same as those considered in Part A of the paper. Exergy analysis is conducted to analyze the component exergy destruction for identification of major exergy destroying components and for their exergy efficiency calculations. However, exergo-economic analysis investigates the effect of plant operating parameters on the fuel and product exergy cost rate(cf and cp), relative cost difference (rk), exergo-economic factor (f) and unit product cost (cp-plant) of the plants. Exergy analysis of the plant shows that an enormous amount of exergy is lost at the gasifier and at the combustion chamber. At higher TITs, exergy efficiency of the major plant components is higher, indicating a better exergetic performance of the plant at elevated TITs. Exergo-economic study indicates that the values of rk, f and unit product cost are 189.69 %, 62.13% and 0.0058 $/MJ at the base case (rp=4 & TIT=1000 °C). Also the value of these parameters increases with increase in rp, for all TITs. However, higher TIT yields in better exergo-economic performance of plant for considered range of rp values.

The effects of hydrogen fuel usage on the exergetic performance of a turbojet engine

In this study, the hydrogen fuel effect on the exergetic performance of a turbojet engine used in a military trainer aircraft is investigated. For the first step, the performance assessments of the exergetic performance are conducted according to jet fuel usage and the actual test cell data of the engine. For the second step, an exergetic evaluation is parametrically estimated to use the hydrogen fuel in the engine. Finally, the performance results of the engine run by jet fuel are compared with the performance results of the engine run by hydrogen fuel. Regarding the results of this study, by using hydrogen fuel in the engine, the exergy efficiency of the engine decreases from 15.40% to 14.33%, while the waste exergy rate increases from 6196.51 kW to 6669.4 kW. At the same time, the exergy rate of the fuel rises from 7324.87 kW to 7785.25 kW, hence the specific fuel exergy of the hydrogen fuel is higher than that of the jet fuel. The waste exergy flow cost of the engine rises from 16.52 × 10−3 US$/kW to 17.79 × 10−3 US$/kW. The environmental effect factor of the engine escalates from 5.49 to 5.98 and the ecological effect factor increases from 6.49 to 6.98. On the other hand, the exergetic sustainability index of the engine reduces from 0.182 to 0.167 when the sustainable efficiency factor of the engine goes down from 1.182 to 1.167. Between the components, for both jet fuel and hydrogen fuel, the CC has the highest values of the fuel exergy waste ratio, the relative waste exergy ratio, the product exergy waste ratio, the fuel ratio indicator, the product ratio indicator, the waste exergy cost flow, the environmental effect factor, the ecological effect factor, and the exergetic improvement potential when the CC has the lowest values of the exergy efficiency, exergetic sustainability index, and sustainable efficiency factor, respectively. The reason for this result is that the combustion process contains high irreversibities. The obtained results indicate that the hydrogen fuel usage in the turbojet engine badly affects the exergetic performance of the engine and its components (especially the combustion chamber) hence the specific exergy of the hydrogen fuel is higher than the jet fuel's. On the other hand, the exhaust emissions emitted to the environment decrease from 0.509 kg/s to 0.0045 kg/s with the hydrogen fuel usage.

A Realistic Approach of the Maximum Work Extraction from Solar Thermal Collectors

In this study, the maximum work extraction from the incident solar energy on solar thermal collectors is investigated by coupling solar collectors with a Carnot machine. A simplified thermal model for the solar collector performance is developed in which the radiation losses play a significant role. In every examined case, the optimum operating temperature that leads to maximum work extraction is calculated. The final results are presented parametrically, covering a great variety of real solar collectors. Moreover, the validation procedure of the developed model proves high accuracy. The results show that non-concentrating collectors should operate up to 400 K while concentrating collectors in higher temperature levels. More specifically, a parabolic trough collector can operate efficiently in temperature levels up to 850 K, while solar dish collectors can operate efficiently in temperature levels up to 1100 K. The results of this study can be exploited for the preliminary design and optimization of solar thermal systems. Moreover, a clear and realistic upper limit concerning the exergy production of solar irradiation with solar thermal collectors is given.

Experimental and theoretical performance investigation of asymmetric photovoltaic/thermal hybrid solar collectors connected in series

Abstract In this study five asymmetric hybrid solar collectors with flat plate receiver connected in series are investigated experimentally and mathematically through analytical expressions deriving from heat transfer and thermodynamics fundamentals. The main objective of this study is to evaluate the collectors' performance in terms of thermal energy and exergy production under various operating conditions thus the experiments are performed at open circuit mode regarding their electrical part and with water as working fluid. Concerning the theoretical analysis, the developed model combines optical, thermal and flow analysis for the determination of both first and second law efficiencies and it is validated against experimental data with an acceptable agreement being observed. Following the model validation, the performance of the collectors is analyzed in terms of thermal and exergy efficiency, thermal losses and absorber temperature. After the thermal analysis, the mathematical model is further developed so as to take into account the electrical production for the overall performance evaluation of the compound parabolic PVT solar collectors. Among the main findings, the final experimental results proved that these solar collectors connected in series work efficiently throughout the year as they are able to produce about 2.2 kW useful energy in summer, 2.8 kW in spring and 2.6 kW in autumn.

Thermodynamic Optimization of a Geothermal- Based Organic Rankine Cycle System Using an Artificial Bee Colony Algorithm

Geothermal energy is a renewable form of energy, however due to misuse, processing and management issues, it is necessary to use the resource more efficiently. To increase energy efficiency, energy systems engineers carry out careful energy control studies and offer alternative solutions. With this aim, this study was conducted to improve the performance of a real operating air-cooled organic Rankine cycle binary geothermal power plant (GPP) and its components in the aspects of thermodynamic modeling, exergy analysis and optimization processes. In-depth information is obtained about the exergy (maximum work a system can make), exergy losses and destruction at the power plant and its components. Thus the performance of the power plant may be predicted with reasonable accuracy and better understanding is gained for the physical process to be used in improving the performance of the power plant. The results of the exergy analysis show that total exergy production rate and exergy efficiency of the GPP are 21 MW and 14.52%, respectively, after removing parasitic loads. The highest amount of exergy destruction occurs, respectively, in condenser 2, vaporizer HH2, condenser 1, pumps 1 and 2 as components requiring priority performance improvement. To maximize the system exergy efficiency, the artificial bee colony (ABC) is applied to the model that simulates the actual GPP. Under all the optimization conditions, the maximum exergy efficiency for the GPP and its components is obtained. Two of these conditions such as Case 4 related to the turbine and Case 12 related to the condenser have the best performance. As a result, the ABC optimization method provides better quality information than exergy analysis. Based on the guidance of this study, the performance of power plants based on geothermal energy and other energy resources may be improved.

New low temperature industrial waste heat district heating system based on natural gas fired boilers with absorption heat exchangers

To efficiently recover low temperature industrial waste heat, a new low temperature industrial waste heat district heating system based on natural gas fired boilers with absorption heat exchangers was proposed, and also analyzed from the perspective of thermodynamics and economics. In heating substations, absorption heat exchangers are used to greatly decrease the return water temperature of the primary heating network. The lower temperature return water helps to efficiently recover waste heat in heating station and greatly increase economic heat transmission distance. Annual primary energy efficiency and product exergy efficiency of the new district heating system are 215.0% and 42.5% respectively. When waste heat price and heat transmission heat distance are 25¥/GJ and 60km respectively, its heating cost and investment recovery period are 6¥/GJ and 0.7years respectively lower than that of current district heating systems based on natural gas fired boilers. Characterized by better thermodynamic performance and economic benefit, the new district heating system would be promising for low-temperature industrial waste heat recovery.

A critical review of definitions for exergetic efficiency in reverse osmosis desalination plants

Different approaches for formulating exergetic efficiency in desalination plants are suggested in literature. In this work these formulations, applied to the reverse osmosis technology, are compared and critically reviewed. As a case study, a reverse osmosis desalination plant in operation has been considered. A key factor is the proper definition of the exergy value of the product and the exergy value of the fuel. In reverse osmosis modules, where chemical separation is carried out, chemical exergy plays also an important role. Another influential issue is the thermodynamic model used in the calculation of the thermodynamic properties. Inappropriate thermodynamic models and ambiguous exergetic efficiency definitions bring confused and contradictory results: negative values of the chemical exergy, exergy production in pumps, or larger irreversibilities in the membranes than in the pumps. The enormous deviations found in the Literature can only be due to different conceptual definitions. In order to clarify these contradictions, this work provides a precise definition for the exergetic efficiency in reverse osmosis desalination plants devices.

Analysis of a gas turbine based hybrid system by utilizing energy, exergy and exergoeconomic methodologies for steam, power and hydrogen production

Energetic, exergetic and exergoeconomic assessments are performed for a novel cogeneration system of power, steam and hydrogen production, including a gas turbine (to produce power), a heat recovery steam generator (to produce steam) and an organic Rankine cycle equipped with a proton exchange membrane electrolyzer (to produce hydrogen). A comprehensive parametric study is reported and effects of such significant variables as air compressor pressure ratio, evaporator temperature, the pinch point temperature difference in the evaporator and degree of the superheat at the ORC turbine inlet on the exergy efficiency, rate of produced hydrogen and sustainability index of the proposed system investigated. Using direct search method by the EES software, the combined system is optimized to achieve the maximum exergy efficiency. It is observed that the rate of produced hydrogen decreases with an increase in superheating degree of ORC turbine and takes the maximum value with change in evaporator temperature. Under the base condition, the corresponding cost values for the power, steam and produced hydrogen are 4.811cents/kWh, 20.56$/ton, and 3.967$/kg H2, respectively. Moreover, under the optimized condition, exergy efficiency, rate of the produced hydrogen and sustainability index of the proposed cogeneration system is 52.09%, 8.723kg/hour and 2.162, respectively.

Modelling and exergoeconomic-environmental analysis of combined cycle power generation system using flameless burner for steam generation

To have an optimum condition for the performance of a combined cycle power generation, using supplementary firing system after gas turbine was investigated by various researchers. Since the temperature of turbine exhaust is higher than auto-ignition temperature of the fuel in optimum condition, using flameless burner is modelled in this paper. Flameless burner is installed between gas turbine cycle and Rankine cycle of a combined cycle power plant which one end is connected to the outlet of gas turbine (as primary combustion oxidizer) and the other end opened to the heat recovery steam generator. Then, the exergoeconomic-environmental analysis of the proposed model is evaluated. Results demonstrate that efficiency of the combined cycle power plant increases about 6% and CO2 emission reduces up to 5.63% in this proposed model. It is found that the variation in the cost is less than 1% due to the fact that a cost constraint is implemented to be equal or lower than the design point cost. Moreover, exergy of flow gases increases in all points except in heat recovery steam generator. Hence, available exergy for work production in both gas cycle and steam cycle will increase in new model.

Exergoeconomic and enviroeconomic analyses of N identical photovoltaic thermal integrated double slope solar still

This paper deals with the enhancement in exergoeconomic and enviroeconomic parameters for double slope solar still by incorporating N identical partially covered photovoltaic thermal (PVT) collectors. The energy, exergy, exergoeconomic and enviroeconomic parameters and productivity have been computed for double slope solar still incorporated with N identical PVT flat plate collectors (N-PVT-FPC-DS). The analysis has been done at 0.14 m water depth, optimum values of mass flow rate and a number of collectors considering four climatic conditions of New Delhi for each month of the year. The result obtained for the proposed system has been compared with the result of earlier researchers. It has been concluded that kWh per unit cost based on exergy gain is higher by 40.73% and 54.63%; environmental cost is higher by 59.70% and 92.55%; however, the output per unit input based on productivity is higher by 9.25% and lower by 25.13% for N-PVT-FPC-DS than double slope solar still integrated with N identical PVT compound parabolic concentrator collector and conventional double slope solar still, respectively.

Thermo-economic analysis and optimization of a combined cooling and power (CCP) system for engine waste heat recovery

A combined cooling and power (CCP) system is developed, which comprises a CO2 Brayton cycle (BC), an organic Rankine cycle (ORC) and an ejector refrigeration cycle for the cascade utilization of waste heat from an internal combustion engine. By establishing mathematical model to simulate the overall system, thermodynamic analysis and exergoeconomic analysis are conducted to examine the effects of five key parameters including the compressor pressure ratio, the compressor inlet temperature, the BC turbine inlet temperature, the ORC turbine inlet pressure and the ejector primary flow pressure on system performance. What’s more, a single-objective optimization by means of genetic algorithm (GA) is carried out to search the optimal system performance from viewpoint of exergoeconomic. Results show that the increases of the BC turbine inlet temperature, the ORC turbine inlet pressure and the ejector primary flow pressure are benefit to both thermodynamic and exergoeconimic performances of the CCP system. However, the rises in compressor pressure ratio and compressor inlet temperature will lead to worse system performances. By the single-objective optimization, the lowest average cost per unit of exergy product for the overall system is obtained.

Numerical calculation of energy and exergy flows of a turboshaft engine for power generation and helicopter applications

Fuel efficiency of aircraft and helicopter becomes greater concern in recent years caused by rising fuel costs and as well as environmental impact of aviation emissions. Modern helicopters, however, highly complex systems with especially turboshaft engines that produce energy and power. So it is important to gain deeper understanding energy and exergy use throughout turboshaft engine and its components. Concurrently, in this study, energy and exergy-based computational approach applied to a turboshaft engine and its components. Exergy efficiency of the axial, centrifugal compressors and power turbine is found to be between 83.8% and 88.6%, while for the combustor, the corresponding value is to be 80.60%. For the components, the greatest exergy efficiency is calculated to be 91.4% at the gas generator turbine unit. As a result of the study, the exergetic efficiency of the turboshaft has been calculated as 27.5% with 1500 kW product exergy. It is expected that numerical formulation based on energy and exergy is beneficial for assessing turboshaft performance for future rotorcraft development.