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This study dealt with evaluating the (J85-GE-5H) military turbojet engine (TJE) in terms of exergetic and advanced exergetic analyses at Military (MIL) and Afterburner (AB) process modes by utilizing kerosene (JP-8) and hydrogen (H2) fuels. First, exergy and advanced exergy analyses of the engine were performed using JP-8 fuel as per actual engine operating conditions. These analyses of the turbojet engine using hydrogen fuel were also examined parametrically. The performance evaluation of the engine was lastly executed by comparing the obtained results for both fuels. Based on the parametric studies undertaken, the entire engine’s exergetic efficiency with JP-8 was reckoned 30.85% at the MIL process mode while it was calculated as 16.98% at the AB process mode. With the usage of H2, the efficiencies of the engine decreased to 28.62% and 15.33% for the above mentioned two modes, respectively. As the supreme exergy destructions occurred in the combustion chamber (CC) and afterburner exhaust duct (ABED) segments, the new technological developments should be considered to design more efficient engines. As a result, the engine worked less efficiently with hydrogen fuel due to the enhancement in exergy destructions. Conversely, the greenhouse gas (GHG) emission parameters lessened with the utilization of H2 fuel.

With the constant increase of energy costs and environmental impacts, improving the process efficiency is considered a priority issue for the manufacturing field. A wide knowledge about materials, energy, machinery, and auxiliary equipment is required in order to optimize the overall performance of manufacturing processes. Sustainability needs to be assessed in order to find an optimal compromise between technical quality of products and environmental compatibility of processes. In this new Industry 4.0 era, innovative manufacturing technologies, as the additive manufacturing, are taking a predominant role. The aim of this work is to give an insight into how thermodynamic laws contribute at the same time to improve energy efficiency of manufacturing resources and to provide a methodological support to move towards a smart and sustainable additive process. In this context, a fundamental step is the proper design of a sensing and real-time monitoring framework of an additive manufacturing process. This framework should be based on an accurate modelling of the physical phenomena and technological aspects of the considered process, taking into account all the sustainability requirements. To this end, a thermodynamic model for the direct laser metal deposition (DLMD) process was proposed as a test case. Finally, an exergetic analysis was conducted on a prototype DLMD system to validate the effectiveness of an ad-hoc monitoring system and highlight the limitations of this process. What emerged is that the proposed framework provided significant advantages, since it represents a valuable approach for finding suitable process management strategies to identify sustainable solutions for innovative manufacturing procedures.

The potential for generating electricity through solar energy makes Brazil a very promising country in this segment, with several possibilities for the use of solar energy, whether in the thermal or photovoltaic part, due to the high incidence of solar radiation throughout much of the country, especially in the Northeast region. In this study, an analysis of the perfor-mance of the organic Rankine cycle (ORC) that produces electricity using solar concentrators was performed. The fluids used in the system were classified as dry type  toluene, isobutane, isopentane, R227ea, R113, R114, R245fa and R600. During the study, the energy and exergy analysis of the system was conducted for different evaporator pressures (500−2500 kPa), and two types of solar collectors were tested (parabolic trough collector and parabolic compound collec-tor). In addition, a system case study was simulated for radiation and temperature conditions in the city of João Pessoa, Brazil. Based on this analysis, the performance of the cycle components was examined, and the first and second law effi-ciencies of the system were compared for different configurations. The solar collector (parabolic trough collector) proved to be the most suitable for the studied cycle. With the adequate selection of the refrigerant, collector and evaporation pressure, the first and second law efficiencies of the cycle improve up to 41% and 44%, respectively. For the city of João Pessoa, the highest exergy efficiency occurs in the month of January, the hottest month of the year when the sun shines brightly, and the lowest exergy efficiency occurs in the month of June.

In this work the thermodynamic performance of a transcritical R744 booster supermarket refrigeration system equipped with R290 dedicated mechanical subcooling (DMS) was exhaustively investigated with the aid of the advanced exergy analysis. The outcomes obtained suggested that improvement priority needs to be addressed to the manufacturing of more efficient high-stage (HS) compressors, followed by the enhancement of the gas cooler/condenser (GC), of the medium-temperature (MT) evaporators, of the R290 compressor, and of the low-temperature (LT) evaporators. These conclusions were different from those drawn by the application of the conventional exergy assessment. Additionally, it was found that GC can be enhanced mainly by reducing the irreversibilities owing to the simultaneous interaction among the components. The R290 compressor would also have significantly benefitted from the adoption of such measures, as half of its avoidable irreversibilities were exogenous. Unlike the aforementioned components, all the evaporators were improvable uniquely by decreasing their temperature difference. Finally, the approach temperature of GC and the outdoor temperature were found to have a noteworthy impact on the avoidable irreversibilities of the investigated solution.

In the current research, a quasi-two-dimensional numerical model is used for energetic and exergetic performance predictions taking into account eight inline PTC modules with variable geometries along with the main flow direction, for Therminol VP-1 and Syltherm 800 heat transfer fluids. There are a total of thirty-seven input variables, being thirty-two regarding the geometrical parameters and five environmental/operating parameters. Surrogate-based optimization procedures (Kriging metamodel combined with Non-Dominated Sorting Genetic Algorithm, NSGA-II) are used to build the Pareto frontier for two objective functions: (i) maximization of both useful gain and thermal efficiency and (ii) maximization of useful gain and minimization of exergy destruction. The optimization results indicated that the useful gain of 8 inline PTC array can reach up to 1.0 MW for both thermal oils. By variation in the input parameters along with the PTC array, a broad range useful gain can be achieved, with negligible thermal efficiency degradation. With regard to the Pareto frontier of useful gain and exergy destruction, there is an important asymptotic point for useful gain, in which its augmentation just promotes the increase in exergy destruction. In terms of concentration ratio, the Pareto fronts showed that about 95% and 90% of PTC modules can be assumed at “heterogeneous” along with the array for the first and second objective functions, respectively. At last, convective heat transfer coefficient and outer receiver and outer glass cover temperatures along with the PTC array for different individuals of the Pareto fronts are discussed in detail. Graphical abstract

The parabolic trough collector (PTC) is one of the most well-established concentrating technologies, and it has been used as a heat source in a wide range of thermal applications which demand relatively higher operating temperatures (about 400 ºC). In the present research, a two-dimensional numerical methodology implemented on EES software (Engineering Equation Solver) is proposed to predict energetic and exergetic performances of commercial PTC modules of EuroTrough ET-150 by considering the discretization of the receiver along with the main flow direction. Different mass flow rates of Therminol VP-1 and Molten Salt (NaNO 3 (60%)–KNO 3 (40%)) heat transfer fluids, receiver diameters and solar beam radiation levels are considered. According to the sensitivity analyses, for turbulent and laminar/transition flow conditions the number of divisions/segments of the PTC module to stabilize the values of useful gain, heat loss and irreversibility of the PTC receiver is 20 and 100 divisions, respectively. The validated model is used to perform detailed energetic and exergetic analyses of a PTC array with eight modules in series, in which the PTC modules are firstly analysed individually and after at an overall thermal performance way. In the second part of this research is presented a case study for the application of ET-150 modules using Therminol VP-1 as heat source for a 3.9 MW Organic Rankine Cycle (ORC) operating under environmental conditions of the Northeast region of Brazil, taking into account its thermo-economic viability. According to thermo-economic assessment, the highest values of Net Present Value (NPV) and Internal Rate of Return (IRR) are achieved for G b  = 700 W m −2 and mass flow rate of 1 kg s −1 . Moreover, for the ORC coupled with fifty rows of PTC and eight modules in a row, the NPV could reach 40 million dollars with about 25% of IRR if exemption from taxes is applied.

After the recent renewed interest in CO2 as the refrigerant (R744) for the food retail industry, many researchers have focused on the performance enhancement of the basic transcritical R744 supermarket refrigeration unit in warm climates. This task is generally fulfilled with the aid of energy-based methods. However, the implementation of an advanced exergy analysis is mandatory to properly evaluate the best strategies needing to be implemented to achieve the greatest thermodynamic performance improvements. Such an assessment, in fact, is widely recognized as the most powerful thermodynamic tool for this purpose. In this work, the advanced exergy analysis was applied to a conventional R744 booster supermarket refrigerating system at the outdoor temperature of 40 °C. The results obtained suggested the adoption of a more sophisticated layout, i.e., the one outfitted with the multi-ejector block. It was found that the multi-ejector supported CO2 system can reduce the total exergy destruction rate by about 39% in comparison with the conventional booster unit. Additionally, the total avoidable exergy destruction rate was decreased from 67.60 to 45.57 kW as well as the total unavoidable exergy destruction rate was brought from 42.67 down to 21.91 kW.

Exergy-based methods provide engineers with the best information with respect to options for improving the overall thermodynamic efficiency of an energy conversion system. This paper presents the results of an advanced exergy analysis of an air-to-water reversible heat pump whose performance was analyzed with respect to different working fluids. Environmentally deleterious refrigerants, i.e., R410A and R134a (baselines), and their eco-friendly replacements (R290, R152a, R1234ze(E), and R1234yf) were selected. The evaluations were conducted under the same operating conditions (i.e., with the same cooling and heating demands and outdoor temperatures). Based on conventional exergy analysis, it was determined that different priorities should be given for the thermodynamic improvement of the components according to which heating and cooling modes of the system are in use. Therefore, integrated parameters, i.e., the annual values of exergy destruction, were applied for further analysis. The results obtained showed that the heat pump using R410A provided the largest degree of annual exergy destruction estimated on the basis of conventional exergy analysis (5913 kWh), whereas the heat pump using R290 offered the lowest one (4522 kWh). The annual exergy destruction of the R410A cycle with only unavoidable irreversibilities could be decreased by 50%. In this case, compared to R410A and R134a, R152a and R290 provided lower values of the total annual unavoidable aspects of exergy destruction. Considering technological limitations, when removing all the avoidable irreversibilities within the air exchanger, the largest decrease in the total exergy destruction within the system could be reached. The results obtained from the analysis of the removable irreversibilities showed that the mutual interactions between the compressor, evaporator, and condenser were weak. Finally, it was concluded that, from a thermodynamic point of view, the adoption of R152a and R290 in reversible air-to-water heat pumps as replacements for R410A and R134a is advisable.

Steam methane reforming (SMR) for hydrogen production was studied by simulating the reformer and pre-reformer sections. This simulation was validated by using available data taken from a real industrial plant, which enabled precise correlations with the real industrial process to be found. Moreover, the influence of the molar ratio between the raw materials (steam-to-carbon molar ratio, S/C) and the reformer outlet temperature (Tcc) was studied. The energy requirements for the reforming reaction increased with the S/C ratio. The energy needed for developing the reforming reaction also increased with Tcc, but the hydrogen yield when operating with a high S/C ratio and Tcc increased. In addition, an exergetic analysis was carried out to identify exergy losses in the SMR process, and most were destroyed in the chemical reactors. Increasing the combustion air flow was proposed for finding an optimum value for exergetic efficiency in the process, thereby reducing fuel consumption. Finally, there was a study into the economic viability of this investment, with a reduction of 22% in utility costs with the optimum exergetic value.

This paper aims to present the real improvement opportunities of a simple organic Rankine cycle (ORC) as waste heat recovery system (WHRS) from the exhaust gases of a natural gas engine using toluene as the working fluid, based on the exergy and environmental point of view. From the energy and exergy balances, the advanced exergetic analysis was developed to determine the irreversibilities and opportunities for improvement. Since the traditional exergo-environmental analysis, it was found that the component with the greatest potential environmental impact associated with exergy (bF = 0.067 mPts/MJ) and per unit of exergy (ḂD = 8.729 mPts/h) was the condenser, while the exergy-environmental fraction was presented in the turbine (52.51%) and pump-2 (21.12%). The advanced exergo-environmental analysis showed that the environmental impact is more associated with the operational behavior of the components, with 75.33% of the environmental impacts being of endogenous nature, showing that the environmental impacts are generated to a reduced magnitude through the interactions between components. However, it was identified that much of the environmental impacts in ITC 1 could be reduced, with 81.3% of these impacts being avoidable. Finally, the sensitivity analysis results revealed that steel is the material of the components with the least environmental impact.