Exergetic Investigation Research Articles

Energetic and exergetic investigation on lauric and stearic acid phase‐change material–based thermal energy storage system integrated with engine exhaust

AbstractEnergy and exergy analysis comparison of lauric and stearic acid phase‐change material (PCM)–based energy storage system integrated with engine exhaust have been investigated in the present study, which provides more realistic assessment than the conventional energy analysis. On the basis of thermodynamic laws, energy, exergy, charging efficiencies, and availability of PCM thermal storage with various mass fractions have been investigated at engine full load. The exergy saved for PCMs in the overall system is quantified and were compared. The results revealed a considerable enhancement in energy and exergy efficiency for thermal energy storage with lauric acid PCM due to its enhanced thermophysical properties. Energy and exergy of the storage medium for lauric acid PCM with 0.4 kg mass fraction, increased by 68% and 57.5% compared with stearic acid PCM thermal storage integrated with a diesel engine. Also, energy and exergy efficiency of charging and integrating the system with stearic acid PCM decrease with increase in mass fractions. Thus, lauric acid PCM can be used as thermal storage medium at high temperatures for exhaust heat recovery from engines and also an option for green technology.

Energetic and exergetic investigations of an innovative heat recovery exhaust system using a double acting type Stirling engine based on theoretical analysis

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 behaviour 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.

Energetic and exergetic investigations of an innovative heat recovery exhaust system using a double acting type Stirling engine based on theoretical analysis

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 behaviour 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.

Energetic and exergetic investigation of a novel refrigeration system utilizing ejector integrated subcooling using different refrigerants

Increase in coefficient of performance of refrigeration systems is eminently important for various applications such as household refrigerator, tumble dryer, and more in practical applications. A new ejector subcooling system is described and investigated numerically without using an extra pump or compressor. After condenser, some part of the liquid (by-pass refrigerant) is expanded so that its temperature could be lower than the intended subcooling temperature. By using this by-pass refrigerant, the main flow of the refrigerant is subcooled. After evaporation, the by-pass refrigerant is expanded using an ejector. Seven different refrigerants are considered as working fluids (namely; R32, R1234yf, R290, R134a, R717, R600a and R245fa). R1234yf, R290, R600a and R717 are considered as low global warming potential refrigerants in European Union regulation. For each refrigerant, the values of coefficient of performance, relative increment in coefficient of performance and exergy efficiencies are calculated and demonstrated graphically for different condenser temperatures between 30°C/70°C and evaporator temperatures between −20°C/10°C. Results show that the best performance is obtained for R1234yf with an increment of about 20% in coefficient of performance and 18% in exergy efficiency. These efficiencies can be higher or lower approximately by 3% using ejector with higher or lower component efficiencies.

Exergetic Investigation of a R1234yf Automotive Air Conditioning System with Internal Heat Exchanger

This study presents the exergetic investigation of an automotive air conditioning (AAC) system with the refrigerant R1234yf experimentally. The air-conditioning system is based on the conventional mechanical compression refrigeration cycle. An internal heat exchanger (IHX) has been added to the system in order to provide performance enhancement. The influence of the IHX investigated at different compressor speeds and air stream temperatures. Experimental measurements were collected by using a data-acquisition system, and the results were obtained by performing exergetic analysis. The exergy destruction, exergy efficiency and the total exergy destruction per cooling capacity were calculated. The analysis results were compared with a baseline system which operates with the refrigerant R134a. Furthermore, an empirical correlation was proposed for the determination of the total exergy destruction per cooling capacity for various compressor speeds for evaluating the system performance without doing further experiments. As a result, the exergetic efficiency of the system was improved by introducing IHX to the system. Moreover, it was observed that the temperature rise in the air stream decreased the exergy efficiency and increased the total exergy destruction per cooling capacity.

Exergo-environmental life cycle assessment of biodiesel production from mutton tallow transesterification

Abstract The main purpose of this study is to comprehensively investigate a biodiesel production system by transesterification of mutton tallow. To this end, an exergo-environmental life cycle assessment was applied. Exergetic investigation identifies the location, magnitude and sources of the thermodynamic inefficiencies in the biodiesel production process (the highest priority components for process improvement from the thermodynamic point of view). In contrast, environmental life cycle assessment identifies the environmental hot spot subsystems of the entire mutton tallow-to-biodiesel system (the highest priority life cycle steps for environmental improvement). The results obtained show that approximately 83.3% of the exergy fed to the process is recovered in the useful product (biodiesel). The transesterification reactor should have the highest priority for process improvement from the thermodynamic point of view. However, the environmental improvements of the entire biodiesel production system should be focused on minimizing methanol consumption. The net energy ratio of the system is approximately 2.3. Therefore, the biodiesel system presents a net energy gain. Using economic allocation instead of the mass-based approach leads to an increase in the life cycle indicators by approximately 11%. However, this difference is only 6.7% when considering energy allocation.

Thermal and exergetic investigation of a solar dish collector operating with mono and hybrid nanofluids

The use of solar dish thermal collectors is a promising choice for designing sustainable energy systems. The use of nanofluids is a new way for enhancing the thermal performance of solar collectors because of their improved thermal properties. The objective of this study is to investigate the use of mono and hybrid nanofluids in a solar dish collector in order to determine which kind of nanofluids leads to higher performance enhancements. The analysis is conducted with a developed thermal model in Engineering Equation Solver and the collector is studied thermally and exergetically. The examined hybrid nanofluid has as base fluid syltherm 800 with 1% Cu and 1% TiO2. Moreover, the examined mono nanofluids are the syltherm 800 with 2% Cu and syltherm 800 with 2% TiO2. The investigated solar dish collector has a spiral absorber and it is examined for inlet temperatures from 25?C up to 300?C with a flow rate of 200 L/h. According to the final results, the use of hybrid nanofluid leads to higher thermal efficiency enhancement compared to the mono nanofluids because of the higher increase in the Nusselt number in the flow. More specifically, the use of the hybrid nanofluids leads to 0.99% mean thermal efficiency enhancement compared to the pure oil case, while the use of Oil/Cu and Oil/TiO2 lead to 0.42% and to 0.56% mean thermal efficiency enhancement, respectively. Moreover, the exergy efficiency is found enhanced with the use of all nanofluids. The mean exergy efficiency enhancement is 1.21% with the hybrid nanofluid, while it is 0.73% with Oil/TiO2 and 0.53% with Oil/Cu.

Energetic And Exergetic Investigations of an Integrated Heat Pump System for Drying Applications

Energetic And Exergetic Investigations of an Integrated Heat Pump System for Drying Applications

Energetic and exergetic analysis of a novel mixture for an absorption/compression refrigeration system: R245fa/DMAC

In this work, an energetic and exergetic investigations of an upgraded frigorific production system, operating a novel organic pair R245fa/DMAC (1,1,1,3,3-Pentafluoropropane/N, N’dimethylacetamide) are performed.Working fluids are selected due to their low GWP (global warming potential). Results relative to the new organic absorbent are compared with those relative to the classical water/ammonia working fluids. Investigated parameters are the COP, the irreversibility and the exergetic efficiency. Results show that the performance coefficient of the system working with the new fluids is similar to that relative to the Ammonia/Water system, the optimum value is about 45% when working with R245fa/DMAC, while the same optimum value is achieved for an intermediate pressure of 600kPa with the classical one. Furthermore, the system using the new proposed pair uses lower threshold temperatures, between 60°C and 80°C as optimum COP, which allows the use of low temperature energy sources. Results of the exergetic analysis indicate that irreversibility of the system working with R245fa/DMAC is lower than that of the system working with Ammonia/Water of about 10kW, for 3kW as refrigeration power, for the optimum operating conditions and so is the exergetic efficiency. It is noted from this study that the major gain brought by this new pair is the diminution of the threshold temperatures from those that go to 120°C to 80°C and even 60°C for such heat pumps. We retain the advantages of introducing this organic absorbent in the refrigeration production field.

Exergetic investigation of a solar dish collector with smooth and corrugated spiral absorber operating with various nanofluids

Solar energy utilization is vital in order to achieve the sustainability and reduce the utilization of conventional energy sources. The use of nanofluids in concentrating solar collectors is a promising solution in order to achieve high performance. This paper examines the use of various nanofluids as working fluids in a solar dish collector with smooth and corrugated absorber tube. The use of Al2O3, Cu, CuO and TiO2 dispersed on thermal oil and water is presented in this work. The examined concentrations of these nanoparticles are up to 5% in this study. The solar collector is investigated exergetically in order to evaluate together the useful thermal output and pressure losses. The analysis is performed with a developed 1-D thermal model and experimental results are used for the model validation for operation with water. According to the final results, the use of oil-based nanofluids leads to higher exergetic efficiency, while the use of water-based nanofluids leads to higher thermal performance. Moreover, the use of Cu nanoparticle is the most suitable exergetically among the examined cases. Generally, the exergetic efficiency of the examined collector is maximized for Cu-oil based nanofluid with the corrugated absorber and it is about 12.29%.

Energetic and exergetic investigations of an innovative light-based hydrogen production reactor

In this study, it is aimed to thermodynamically study and experimentally test a continuous type hybrid photoelectrochemical hydrogen production system. The hybrid system considered in this study is capable of enhancing solar spectrum utilization via the combination of photocatalysis and PV/T. In addition, the system eliminates the electron donor requirement of photocatalysis by employing photoelectrodes. Which, as a result, risk of potentially harmful pollutant emissions is reduced. In this study, the present system is investigated in electrolysis operation under three different inlet mass flow rates (0.25, 0.50, and 0.75 g/s). The experimental results are compared to the thermodynamic model outputs. Parametric studies are conducted by changing the inlet mass flow rate from 0 to 1 g/s. The present experimental results suggest that the highest hydrogen production rate is observed at 0.75 g/s inlet mass flow rate, which is 2.43 mg/h. The highest energy and exergy efficiencies are calculated at 0.25 g/s, which are 36% and 32%, respectively. Furthermore, thermodynamic model outputs are confirmed to have a good agreement with the experimental results.

Performance and exergetic investigation of a domestic sp

Performance and exergetic investigation of a domestic sp

Energetic and exergetic investigation of a novel solar assisted mechanical compression refrigeration system

The objective of this study is to present and to examine a novel solar assisted mechanical compression refrigeration system. Evacuated tube collectors are used in order to partially thermally compress the refrigerant, after the mechanical compressor. This design aims to reduce the electricity consumption using a renewable energy source, creating a sustainable system. The suggested design is analyzed parametrically in order to investigate its energetic and exergetic behaviour in various operating conditions and it is examined with EES (Engineering Equator Solver) in steady state conditions. The temperature levels in the evaporator and in the condenser, as well as the thermal compression fraction (expressed with the pressure ratio parameter), are the examined parameters. The final results proved that the optimum values of the pressure after the mechanical compressor is the 75% of the maximum pressure and for this case, energy savings from 15% to 25% can be achieved. Moreover, the specific collecting area is found to be relatively low, close to 2m2/kW for the optimum cases. The final results proved that the new design leads to energy savings in all the examined cases and especially in cases with higher evaporating temperature levels, a fact that makes it ideal for space cooling applications.

Energetic and Exergetic Investigation of a N 2 O Ejector Expansion Transcritical Refrigeration Cycle

Abstract Thermodynamic analysis of a transcritical N2O ejector expansion refrigeration cycle is analysed. A two phase ejector, as an expansion device, is used in place of a conventional expansion valve. Effect of three performance parameters for cycle, namely COP, refrigerating effect, compressor work and two performance parameters of ejectors namely entrainment ratio and pressure recovery ratio are evaluated for various motive nozzle inlet conditions and evaporator temperatures. Further, both energetic and exergetic comparison of the proposed cycle is presented with respect to conventional CO2 ejector expansion refrigeration cycle. The N2O ejector expansion system is found to have higher COP, lower compressor discharge pressure and higher entrainment ratio but have disadvantage of lower volumetric cooling capacity. Maximum COP of N2O ejector cycle is found to be about 10% higher than maximum COP of CO2 ejector cycle. Exergetic output of N2O ejector cycle is higher whereas losses occurred due to irreversibility during expansion is lower.

Energetic and exergetic investigation of a parabolic trough collector with internal fins operating with carbon dioxide

The objective of this study is to determine the energetic and exergetic enhancement of parabolic trough collector with internal fins in the absorber. Carbon dioxide is the examined working fluid to investigate the performance of the system in high temperature levels. In the first part of this study, the impact of the mass flow rate on the collector performance is analyzed and finally 0.20 kg/s is selected as the most appropriate mass flow rate exergetically. In the second part, the impact of internal fins on the system performance is investigated for operation with the optimum mass flow rate. More specifically, the absorber without fins is compared with three different fins with lengths 5, 10 and 15 mm. The final results prove that the higher fin length increases the thermal performance, while the optimum fin length exergetically is 10 mm with 45.95% exergetic efficiency when the inlet temperature is equal to 400 °C. The impact of the pressure losses along the collector is taken into account in the exergetic efficiency, which is the best index for evaluating solar collectors operating with gases. The analysis is performed with Solidworks Flow Simulation, a powerful tool which allows the simultaneous thermal and optical analysis.

Energetic and exergetic performance investigation of a cement facility for clinker production

Energetic and exergetic performance investigation of a cement facility for clinker production

Energetic and exergetic performance investigation of a cement facility for clinker production

In this study, the energetic and exergetic analyses of a cement plant for clinker production are investigated. The exergy destruction rate, energy and exergy efficiency of process components are presented by using the thermodynamic balance equations. The energetic and exergetic efficiencies of cement plant are calculated as 60.78%, and 46.11%, respectively. The rotary kiln, raw mill and cooler component have the maximum exergy destruction rate among the other process components. The exergy efficiency of rotary kiln, raw mill and cooler component are calculated as 57.36%, 33.52% and 49.46%, respectively. Also, to analyse the cement plant performance more comprehensively, the parametric studies are conducted to determine the impacts of different design variables, such as rotary kiln temperature and raw material mass flow rate, and feedstock coal chemical properties and varying of ambient temperature on the energy efficiency, exergy efficiency and exergy destruction rate of plant components.

Experimental analysis, hybridization and exergetic investigation of an absorption refrigeration unit

In this work, an experimental and theoretical investigation of a frozen and hot water production unit with direct gas absorption is developed. Water/ammonia couple is used.A particular interest is given to the system performances evaluation such as exergetic efficiency and total exergy loss. Parameters analyzed are coefficients of performance, irreversibility and exergetic efficiency.Results show that the machine can reach a COP up to 65% and exergetic efficiency up to 18% for a working temperature and a condensation temperature of 120 °C and 18 °C, respectively. These performances decrease for a condensation temperature of 37 °C and 47 °C. Indeed, the engine is less efficient and presents more irreversibility, which is major in the pre-absorber and the absorber.An improvement of the machine cycle is proposed, in order to adapt it to low grade heat sources, using a compressor upstream of the pre-absorber. Performances of the new hybrid cycle are better than those of the real cycle.

Energy and exergy analysis as tools for optimization of hydrogen production by glycerol autothermal reforming

In this work, various assessment tools were comprehensively applied to investigate hydrogen production via glycerol autothermal reforming. These tools are used to study the chemical reactions, design and simulate the entire hydrogen production process, investigate the energetic and exergetic performances of the processes and perform parametric analyses (using intuitive and design of experiment-based methods).Investigating the chemical reactions of autothermal reforming (ATR) of glycerol reveals that the optimal conditions, based on maximizing the hydrogen production, minimizing the methane and carbon monoxide contents and eliminating coke formation at thermoneutral conditions, can be achieved at a water–glycerol feed ratio (WGFR), reforming temperature (T) and oxygen–glycerol feed ratio (OGFR) of 9, 900 K and 0.35, respectively. The energetic study of the resulting process indicates that approximately two-thirds of the energy fed to the process is recovered in the useful product (H2) and that the remaining incoming process energy is exhausted in the off-gas. The exergetic investigation reveals that the exergetic efficiency of the ATR process is 57% and that 152 kJ are destroyed to generate 1 mol of hydrogen. The process operating conditions recommended by the chemical reaction investigation suffers from low performance because energetic and exergetic efficiencies are comparatively lower than values previously reported in literature for other reformates. The parametric investigation indicates that more accurate conditions are needed to convert glycerol–hydrogen. These conditions ensure the lowest consumption of energy to generate a given amount of hydrogen. This paper recommends WGFR = 5.5, T = 900 K and OGFR = 0.96 as the optimum conditions for the entire glycerol-to-hydrogen process. For this configuration, the thermal and exergetic efficiencies are 78.7% and 67.8%, respectively.

Energetic and exergetic investigation of novel multi-flash geothermal systems integrated with electrolyzers

In this paper, a comparative energetic and exergetic study is conducted to analyze novel multi-flash (single to quintuple) geothermal power generating systems which are newly integrated with electrolyzers for hydrogen production. The effects of increasing the number of flashing from one to five for the system on its performance are carefully studied for practical applications. In addition, parametric studies are undertaken to investigate the effects of varying several operating conditions on the performance of the integrated multi-flash systems. The results show that increasing ambient temperature results in smaller exergy destruction rates and higher overall exergy efficiencies. Furthermore, the quintuple-flash system integrated with electrolyzer provides the largest power output and the highest energy and exergy efficiencies among the systems considered. The power generation, hydrogen production rate and overall energy and exergy efficiencies of the quintuple flash integrated system are found to be varying from 6.8 kW to 112.9 kW, 2.6 L s−1 to 44.21 L s−1, 2.8%–4.6%, and 46.5%–53.4%, respectively, by increasing the geothermal source temperature.