Search Results (77)

Dill is a valuable herb recognized for its rich nutritional composition and bioactive properties. Drying is an efficient preservation technique for maintaining its quality characteristics and ensuring longer storage stability. Incorporating ultrasonic pretreatment before the drying process can significantly reduce energy consumption (SEC) and greenhouse gas emissions. To the best of our knowledge, this is the first study to comprehensively evaluate ultrasound-assisted hybrid microwave–convective drying of dill (Anethum graveolens L.) leaves, focusing on the combined effects on drying kinetics, energetic and exergetic performance, providing an indirect emission estimate and multiple quality attributes. This study aimed to evaluate the drying kinetics, energy and exergy performance parameters, greenhouse gas emissions, quality properties (water activity, rehydration ratio and color) and antioxidant capacity of dill leaves dried by the microwave–hot-air (MW-HA) technique combined with ultrasonic (US) pretreatment. The experiments were conducted at MW power levels of 20%, 40%, and 60% (corresponding to a total output of 900 W), air temperatures of 40 and 60 °C, and US pretreatment durations of 0, 10, and 30 min. The results illustrated that rising MW power, air temperature and US duration significantly reduced the drying time, SEC and greenhouse gas emissions. At higher process conditions, specifically, 40% MW power, 60 °C drying temperature, and 30 min US pretreatment, the maximum energy efficiency (10.17%) and exergy efficiency (11.35%) were obtained. In terms of quality attributes, the best results were achieved at 40% MW power, 60 °C air temperature, and 10 min ultrasonic pretreatment, with reduced water activity (0.258), minimal color variation (ΔE = 11.44), improved rehydration ratio (3.88), and high retention of antioxidant activity. These findings demonstrate the potential of ultrasound pretreatment to enhance drying performance by reducing energy use and emissions while improving quality and antioxidant retention in dill, offering new guidelines for sustainable processing of this herb. Future studies should optimize microwave–hot-air-drying conditions to balance energy efficiency, exergy, and product quality. Full article

Desalination is an increasingly important element in the sustainable supply of potable water. To accurately predict costs, the efficiency of such systems requires accurate knowledge of seawater’s thermodynamic properties. Four models have been proposed for determining the thermophysical properties of salt water, pure water, an ideal mixture, and an aqueous sodium chloride solution, and empirical correlations, as would be expected, provide the precision necessary for accurate exergy calculations. This research began with a study of the most recent and accurate empirical investigations of the thermodynamic properties of seawater. It then employed AI techniques to develop a simpler, more accurate model for density, Gibbs free energy, specific enthalpy, and specific entropy for pressures extending up to 12 MPa, salinities from 0 to 80 g/kg, and the temperature range of 10 °C to 120 °C. The AI-based correlations achieved absolute errors of 1.5 kg/m³ for density, 0.185 kJ/kg for specific enthalpy, 0.005 kJ/kg·K for specific entropy, and 0.214 kJ/kg for Gibbs free energy. These values demonstrated at least equivalent, and even superior, accuracy to the existing state-of-the-art formulations, with the advantage of significantly reduced computational complexity, enhanced computational efficiency, and a more user-friendly implementation. Validation against experimental data demonstrated the exceptional accuracy of the predicted values for all the stated thermodynamic properties. In addition, an exergy-based assessment was conducted of the performance of a recently commissioned desalination plant in Kuwait. This was a large-scale multi-effect distillation plant with thermal vapour compression (MED-TVC), showing a second-law efficiency of 8.9%, with the primary source of exergy destruction identified as the evaporator units. Comparative assessment with a more conventional approach showed differences of less than 0.4% in total exergy destruction and less than 5% in exergetic efficiency. This is taken as a validation of the accuracy, reliability, and practical usefulness of the proposed AI framework for the performance evaluation of desalination systems. Full article

Recently, numerous nations have found themselves in urgent need of an effective water desalination method that utilizes less energy and addresses water scarcity. A low-pressure desalination system is an appropriate technology for many regions due to its benefits, including minimal energy usage to achieve the evaporation threshold, substantial water output, and high-quality pure water. This work primarily aims to ensure the sustainability of low-pressure solar-powered desalination technology combined with a finned natural air-cooling condenser by providing a comprehensive analysis of the exergy, economic, and environmental aspects. Furthermore, innovative technology is a pioneer in generating freshwater continuously without affecting system pressure. Ambient temperature serves as a crucial sign of climate conditions, influencing the level of freshwater productivity, particularly when utilizing a natural air-cooled condenser. Consequently, this temperature has been thoroughly investigated through experiments and exergy analysis. Under the optimal conditions for this study, h_sw = 15 cm, T_sw = 80 °C, and T_amb = 28 °C, the maximum productivity and GOR were obtained as 1020 g/hr and 1.2, respectively. Exergetic efficiency can reach a maximum of 3.48%. The economic analysis of the proposed system indicates that the cost of freshwater productivity is USD 0.042 per kilogram. Furthermore, the device’s first cost recovery period is roughly 183 days or 3.6% of its lifetime. The quantity and price of diluted CO₂ over the lifetime of the device are 13 tons of CO₂/year and 188.5 USD/year, respectively. Full article

In cryogenic air liquefaction systems, a major share of the mechanical energy consumption is associated with exergy destruction caused by heat transfer in recuperative heat exchangers. This study investigated the exergetic optimization of cryogenic gas separation systems by focusing on the Claude–Heylandt cycle as an advanced structural modification of the classical Linde–Hampson scheme. An exergy-based analysis demonstrates that minimizing mechanical energy consumption requires a progressive reduction in the temperature difference between the hot forward stream and the cold returning stream toward the cold end of the heat exchanger. This condition was achieved by extracting a fraction of the high-pressure stream and expanding it in a parallel expander, thereby creating a controlled imbalance in the heat capacities between the two streams. The proposed configuration reduces the share of exergy destruction associated with heat transfer in the recuperative heat exchanger from 14% to 3.5%, leading to a fourfold increase in the exergetic efficiency, together with a 3.6-fold increase in the liquefied air fraction compared with the Linde–Hampson cycle operating under identical conditions. The effects of key decision parameters, including the compression pressure, imposed temperature differences, and expander inlet temperature, were systematically analyzed. The study was further extended by integrating an air separation column into the Claude–Heylandt cycle and optimizing its configuration based on entropy generation minimization. The optimal liquid-air feeding height and threshold number of rectification trays were identified, beyond which further structural complexity yielded no thermodynamic benefit. The results highlight the effectiveness of exergy-based optimization as a unified design criterion for both cryogenic liquefaction and separation processes. Full article

Despite substantial advances in turbofan engineering, a crucial gap persists: there remains the need for an all-inclusive comparative analysis that includes real-world operational data and evaluates the performance of modern turbofans used in aviation. Specifically, systematic investigations that examine the exergy and efficiency of turbofan engines for takeoff and cruise remain scarce. Further, the current literature needs to address rigorous performance assessments that include simultaneous consideration of the combined effects of ambient conditions (e.g., temperature, density, relative humidity), Mach number, and turbine inlet temperature on high-bypass turbofan engines used in modern, commercial aircraft. Energetic and exergetic analyses were conducted on five commercial high-bypass turbofan engines with different configurations for both takeoff and cruise flight modes. The computational thermodynamic models developed showed strong correlation with manufacturers’ specifications. Performance evaluations included variations in ambient conditions, altitude, Mach number, and turbine inlet temperature. Results demonstrate that three-spool engine architecture exhibits 70–71% reduction in exergy destruction between flight phases compared to 62.5% for two-spool designs, indicating greater operational adaptability. The combustion chamber emerged as the dominant contributor to irreversibilities, representing approximately 55–58% of overall exergy destruction during takeoff operations. Results demonstrate that increased ambient temperature and/or humidity increase both degraded exergetic efficiency and thrust-specific fuel consumption, and that Mach number and altitude influenced efficiency metrics through ram compression and density effects, while higher turbine inlet temperatures enhanced exhaust kinetic energy via increased thermal input. We show that cruise operations demonstrated superior exergetic efficiency (68–74%) compared with takeoff (47–60%) across all engine configurations. Our results confirm the fundamental trade-off in turbofan design: for long-range applications, high-bypass engines prioritize propulsive efficiency, while for power-intensive operations, moderate-bypass configurations deliver higher specific thrust. Full article

Geothermal energy is a renewable and sustainable resource, but its efficient utilization is often constrained by operational inefficiencies and inadequate system management, highlighting the need for detailed energy assessments to improve performance and ensure long-term sustainability. This study aims for a comparative assessment of the performance of a binary geothermal power plant (GPP) considering air-cooled and evaporative cooling configurations using exergy analysis, based on real operating data. Exergetic parameters were applied to evaluate both overall system efficiency and the performance of individual components. The effect of geothermal fluid mass flow rate on turbine net power output was investigated. Additionally, a carbon emission analysis was conducted to assess environmental impact. Based on the energy content of the geothermal fluid entering the heat exchanger, the plant’s energy efficiency was calculated to be 7.5% for the air-cooled condenser configuration and 8.5% for the evaporative condenser configuration. On the basis of the heat input to the Rankine cycle, the overall energy efficiencies of the plant were found to be 39.76% and 43% for the air-cooled and evaporative condenser cases, respectively. The findings suggest that the overall exergy efficiency of the plant improves when employing the evaporative cooling system, reaching 53.57% compared to 48.38% for the air-cooled system. In the air-cooled configuration, Condenser I accounted for the highest exergy destruction at 27%, whereas in the evaporative system, Vaporizer II had the largest share at 25%. Furthermore, it was determined that the plant with an evaporative cooling system produced approximately 13% less carbon emissions compared to the air-cooled plant, which represents an advantage in terms of environmental sustainability. Full article

Since the hydrogen-production process is not yet fully efficient, this paper proposes a poly-generation system that is driven by a geothermal energy source and utilizes a combined Kalina/organic Rankine cycle coupled with an electrolyzer unit to produce, simultaneously, power and green hydrogen in an efficient way. A comprehensive thermodynamic analysis and an exergetic evaluation are carried out to assess the effect of key system parameters (geothermal temperature, high pressure, ammonia–water concentration ratio, and terminal thermal difference) on the performance of concurrent production of power and green hydrogen. Thereby, two configurations are investigated with/without the separation of turbines. The optimal ammonia mass fraction of the basic solution in KC is identified, which leads to an overall optimal system performance in terms of exergy efficiency and green hydrogen production rate. In both configurations, the optimal evaluation is made possible by conducting a genetic algorithm optimization. The simulation results without/with the separation of turbines demonstrate the potential of the suggested cycle combination and emphasize its effectiveness and efficiency. Exemplary, for the case without the separation of turbines, it turns out that the combination of ammonia–water and MD2M provides the best performance with net power of 1470 kW, energy efficiency of 0.1184, and exergy efficiency of 0.1258 while producing a significant green hydrogen amount of 620.17 kg/day. Finally, an economic study allows to determine the total investment and payback time of $3,342,000 and 5.37 years, respectively. The levelized cost of hydrogen (LCOH) for the proposed system is estimated at 3.007 USD/kg H₂, aligning well with values reported in the literature. Full article

Creole avocado is the second most widely produced and consumed variety of avocado globally. Due to its commercialization, limited studies have explored its potential for sustainable applications in biorefinery, particularly focusing on reusing the significant amount of waste generated during its consumption. This research evaluates thermodynamic energy losses of a Creole avocado extractive-based biorefinery, which are of critical importance during the fruit valorization process to determine the efficiency and possibilities of optimization, as well as sustainability impacts, through an exergy balance using computer-aided process engineering. The proposed method utilizes the whole fruit to produce three primary bioproducts, with a focus on implementation in the Montes de María region of Colombia. Following the extended mass and energy balance, an in-depth exergetic analysis was conducted, revealing that all process stages exhibited an exergetic efficiency exceeding 50%. The irreversibilities of the process were calculated as 7763.74 MJ/h, the total waste exergy was 2924.42 MJ/h, and the exergy from industrial waste amounted to 7800.42 MJ/h. These findings highlight the potential for optimizing the sustainability of avocado-based production systems through computer-aided analysis as an effective method. This approach accurately identifies exergy losses at each stage, providing precise numerical data and graphical representations. Additionally, it underscores not only the environmental benefits but also the contribution of these systems to enhancing energy efficiency in agro-industrial applications. Full article

The transition towards sustainable energy systems demands efficient utilization of low- and medium-temperature thermal sources, which offer a promising alternative to pollutant energy carriers like fossil fuels. Among these, solar thermal, geothermal, and residual heat emerge as leading candidates for clean energy generation. Organic Rankine Cycles (ORCs) stand out as robust technologies capable of converting these thermal sources into electricity with high efficiency. A critical factor in ORC performance lies in the effective transfer of heat from the thermal source to the working fluid. This study systematically evaluates various thermal oils as intermediate heat transfer media, aiming to optimize their selection based on key performance indicators. The analysis focuses on thermal and exergetic efficiencies, alongside mass and volumetric flow rates of both the working fluid and the thermal oil. The findings reveal that the integration of thermal oils notably boosts the exergetic efficiency of the ORC system, underscoring their pivotal role in maximizing energy conversion from sustainable heat sources. Full article

In “no-bleed” engine architectures, bleed air is replaced by shaft power extraction to run the subsystems, avoiding the inefficiencies of traditional bleed systems. This approach is increasingly used in small turbofan engines, prompting analysis of its impact on engine performance and exergy efficiency. A small high-bypass turbofan engine was modeled in software under two control strategies: constant thrust (CT) and constant speed (CS), with shaft power extraction up to 18 kW. Exergy analysis evaluated efficiency losses and sustainability metrics (exergy efficiency, environmental effect factor, and exergetic sustainability index). Simulations indicate that an 18 kW shaft power extraction increases SFC by 13.6% (CT) and 42.1% (CS). Exergy efficiency rises from 47.3% to 50.7% (CT) and 54.2% (CS). However, these power draws also increase irreversibility and the environmental effect factor (EEF) grows from 0.678 to 0.732 (CT) and 0.744 (CS), while the exergetic sustainability index (ESI) drops from 1.48 to 1.34, signaling reduced sustainability at high extraction. Maintaining constant thrust during extraction incurs smaller fuel consumption and exergy efficiency penalties than constant speed control. The findings highlight the need for adaptive control strategies (e.g., limiting extraction levels or using variable-geometry components) to mitigate losses and enhance sustainability in no-bleed engine designs. Full article

This study investigates the effects of novel pipe cross-section designs on the thermal, hydraulic, and exergetic performance of a double-pipe heat exchanger, aiming to identify the most efficient design for industrial applications. Four novel cross-sections are proposed: Case 1 (rounded square), Case 2 (hexagonal), Case 3 (triangular), and Case 4 (star-like), all maintaining the same inlet area as the base model (circular). A 3D CFD model using the Finite Volume Method and realizable k-ε turbulence model is employed to analyze performance under turbulent flow conditions (Re = 3000–20,000). Key metrics, including the Nusselt number, overall heat transfer coefficient, pressure drop, and exergy destruction, are evaluated. The results show that Case 2 achieves a 7% increase in the Nusselt number at Re = 3000 and a 2% increase at Re = 20,000, while Case 4 exhibits a 180% improvement in the overall heat transfer coefficient at Re = 13,100. However, Case 4’s higher pressure drop reduces its performance compared to the base model. Case 2 demonstrates the best thermal characteristics, making it the most suitable for industrial applications. Full article

Heat pump-based renewable energy and waste heat recycling have become a mainstay of sustainable heating. Still, configuring an effective control system for these purposes remains a worthwhile research topic. In this study, a Smith-predictor-based fractional-order PID cascade control system was fitted into an actual clean heating renovation project and an advanced fireworks algorithm was used to tune the structural parameters of the controllers adaptively. Specifically, three improvements in the fireworks algorithm, including the Cauchy mutation strategy, the adaptive explosion radius, and the elite random selection strategy, contributed to the effectiveness of the tuning process. Simulation and field investigation results demonstrated that the fitted control system counters the adverse effects of time lag, reduces overshoot, and shortens the settling time. Further, benefiting from a delicate balance between heating demand and supply, the heating system with upgraded management increases the average exergetic efficiency by 11.4% and decreases the complaint rate by 76.5%. It is worth noting that the advanced fireworks algorithm mitigates the adverse effect of capacity lag and simultaneously accelerates the optimizing and converging processes, exhibiting its comprehensive competitiveness among this study’s three intelligent optimization algorithms. Meanwhile, the forecast and regulation of the return water temperature of the heating system are independent of each other. In the future, an investigation into the implications of such independence on the control strategy and overall efficiency of the heating system, as well as how an integral predictive control structure might address this limitation, will be worthwhile. Full article

Using polygeneration systems is one of the most cost-effective ways for energy efficiency improvement, which secures sustainable energy development and reduces environmental impacts. This paper investigates a polygeneration system powered by low- to medium-grade waste heat and using CO₂ as a working fluid to simultaneously produce electric power, refrigeration, and heating capacities. The system is simulated in Aspen HYSYS^® and evaluated by applying advanced exergy-based methods. With the split of exergy destruction and investment cost into avoidable and unavoidable parts, the avoidable part reveals the real improvement potential and priority of each component. Subsequently, an exergoeconomic graphical optimization is implemented at the component level to improve the system performance further. Optimization results and an engineering solution considering technical limitations are proposed. Compared to the base case, the system exergetic efficiency was improved by 15.4% and the average product cost was reduced by 7.1%; while the engineering solution shows an increase of 11.3% in system exergetic efficiency and a decrease of 8.5% in the average product cost. Full article

This paper concerns an economic and exergetic efficiency analysis of a plate heat exchanger placed in a solar installation with TiO₂:SiO₂/DI:EG nanofluid. This device separates the primary circuit—with the solar fluid—and the secondary circuit—in which domestic hot water flows (DHW). The solar fluid is TiO₂:SiO₂ nanofluid with a concentration in the range of 0.5–1.5%vol. and T = 60 °C. Its flow is maintained at a constant level of 3 dm³/min. The heat-receiving medium is domestic water with an initial temperature of 30 °C. This work records a DHW flow of ${\dot{V}}_{DHW,in}$ = 3–6(12) dm³/min. In order to calculate the exergy efficiency of the system, first, the total exergy destruction, the entropy generation number N_s, and the Bejan number Be are determined. Only for a comparable solar fluid flow, DHW ${\dot{V}}_{nf}={\dot{V}}_{DHW}$ 3 dm³/min, and concentrations of 0 and 0.5%vol. is there no significant improvement in the exergy efficiency. In other cases, the presence of nanoparticles significantly improves the heat transfer. The TiO₂:SiO₂/DI:EG nanofluid is even a 13 to 26% more effective working fluid than the traditional solar fluid; at Re = 329, the exergy efficiency is ${\eta }_{exergy}$ = 37.29%, with a nanoparticle concentration of 0% and ${\eta }_{exergy}$(1.5%vol.) = 50.56%; with Re = 430, ${\eta }_{exergy}$(0%) = 57.03% and ${\eta }_{exergy}$(1.5%) = 65.9%. Full article

The interest in combined heat and solar power (CHP) systems has increased due to the growing demand for sustainable energy with low carbon emissions. An effective technical solution to address this requirement is using a parabolic trough solar collector (PTC) in conjunction with a Rankine cycle (RC) heat engine. The solar-powered Rankine cycle (SPRC) system is a renewable energy technology that can be relied upon for its high efficiency and produces clean energy output. This study describes developing a SPRC system specifically for electricity generation in Aden, Yemen. The system comprises parabolic trough collectors, a thermal storage tank, and a Rankine cycle. A 4E analysis of this system was theoretically investigated, and the effects of various design conditions, namely the boiler’s pinch point temperature and steam extraction from the high-pressure turbine, steam extraction from the intermediate-pressure turbine, and condenser temperature, were studied. Numerical simulations showed that the system produces a 50 MW net. The system’s exergetic and energy efficiencies are 30.7% and 32.4%. The planned system costs 2509 USD/h, the exergoeconomic factor is 79.43%, and the system’s energy cost is 50.19 USD/MWh. The system has a 22.47 kg/MWh environmental carbon footprint. It is also observed that the performance of the cycle is greatly influenced by climatic circumstances. Raising the boiler’s pinch point temperature decreases the system’s performance and raises the environmental impact. Full article