Search Results (794)

A novel open-loop thermosyphon heat engine driven by low-temperature waste heat is proposed for simultaneous power generation and freshwater production. Large quantities of low-grade thermal energy from sources such as data centres remain underutilised due to the limited efficiency and mechanical complexity of conventional heat engines at low temperatures. The proposed system employs thermosyphon-driven circulation and gravity-assisted condensate return, eliminating mechanical pumping and reducing parasitic losses. A mathematical model was developed to evaluate system performance under low-grade heat input conditions. For a baseline case with 50% turbine isentropic efficiency and 5000 W thermal input, the model predicts an overall efficiency of 3.8% and freshwater production of 143 kg/day. A parametric study was conducted to identify the dominant performance parameters and assess sensitivity to operating conditions. While the predicted power output does not exceed that of optimised Organic Rankine Cycle systems, the proposed configuration offers reduced mechanical complexity and inherent freshwater production through phase change. Unlike membrane-based desalination systems, the open-loop design can accommodate high-salinity feeds, including concentrated brine streams, enabling high recovery operation. These characteristics suggest potential application in low-temperature waste heat recovery scenarios where simplified operation, high-salinity tolerance, and combined energy–water generation are desirable. Full article

Renewable energy sources, such as solar and biomass, represent sustainable alternatives to meet the growing energy demands of the residential sector. This study evaluated the energy, exergy, and environmental performance of two Brayton configurations using supercritical carbon dioxide: a recompression cycle (SRC) and a recompression cycle with intercooling in the main compression (SMC), both coupled to a dual-loop organic Rankine cycle (DORC) and powered by a hybrid solar-biomass thermal system. Mass, energy, and exergy balances were developed, and a life cycle assessment was performed to quantify the environmental impact. The systems were designed to cover a cooling load of 130 kW corresponding to 200 dwellings constructed with Asbestos cement in the Colombian Caribbean region. The results show that both configurations meet the required demand; the SMC-DORC cycle operates at 650 °C, while the SRC-DORC requires 750 °C. The SRC-DORC exhibits higher thermal efficiency (53.24%), while the SMC-DORC achieves a slightly higher exergy efficiency (28.15%). Environmental analysis shows that the construction phase accounts for the majority of the total impact, exceeding 95% of emissions. Overall, both configurations are technically feasible, with the SRC-DORC standing out for its balance between efficiency and environmental impact. Full article

Organic Rankine Cycles (ORCs) are widely recognized as an effective solution for Waste heat recovery (WHR). However, the design and optimization of these systems must address the tradeoff between computational efficiency and the need to capture complex component behavior. This requires moving beyond purely energetic 0D modeling approaches to account for constructional, spatial, and operational constraints. This work presents a novel modeling framework with a specific focus on the expansion device. Radial inflow turbine stages are selected for their capability to achieve high pressure ratios while maintaining compactness and high efficiency. Heat exchangers follow a generic one-dimensional counterflow configuration, with a shell-and-tube geometry adopted for sizing purposes. The turbine stages are modeled by resolving several internal sections in order to capture local thermofluid dynamic conditions. The framework predicts turbine efficiency and incorporates a newly developed formulation for shock-induced losses, improving performance prediction under trans-sonic flow conditions. After validation against experimental data, the model is applied to a WHR system integrated with an internal combustion engine fueled by biofuels. The results highlight the existence of optimal operating conditions arising from competing physical mechanisms. The analysis also shows the transition from single-stage to two-stage turbine configurations at high pressure ratios and emphasizes the role of real gas effects in determining stage performance and optimal expansion distribution. The results of simulations carried out for three different working fluids (ethanol, toluene, and R1234ze(E)) highlight that the available mechanical power ranges from 10 to 22 kW for single-stage turbine configurations and from 24 to 36 kW for two-stage configurations, with total system volumes varying between approximately 600 and 9000 L. Among the working fluids considered here, ethanol provides the best overall performance for the present case study. Overall, the proposed approach provides a reliable and computationally efficient tool for the preliminary design and optimization of ORC-based WHR systems. Full article

To explicitly illustrate the relationship between heliostat field optimization and power generation, a coupled model was established in Simulink. By optimizing the geometric layout of the heliostat field, the solar heat collection efficiency can be significantly improved, thereby increasing the thermal input to the system. The optimized heliostat field design can convert solar energy into thermal energy more efficiently and transfer it to the steam generator through the molten salt loop, thereby driving power generation in the Rankine cycle. In this process, the Rankine cycle is responsible for converting the thermal energy supplied by the molten salt loop into mechanical work and ultimately into electrical power output. At the same time, real meteorological data from a commercial heliostat field were introduced, and annual power generation simulations demonstrated that the integrated modeling of the heliostat field, thermal storage, and power block based on actual meteorological boundary conditions and system parameters can effectively reflect the power generation performance of a commercial tower solar thermal power plant. Meanwhile, research on heliostat field optimization should further evolve from identifying general patterns toward parameter design and overall system performance improvement. For molten-salt tower solar thermal power plants, key design variables such as receiver tower height, receiver dimensions, heliostat dimensions, and heliostat field spacing parameters affect not only the annual average optical efficiency of the heliostat field and the thermal power output of the receiver, but also the annual power generation of the entire plant. By integrating SOLARPILOT 1.5.2 and SAM 2025.4.16, the design variables were systematically analyzed to investigate their effects on the annual average optical efficiency of the heliostat field, the number of heliostats, the receiver output power, and the annual power generation, and the reasonable value ranges of the heliostat field parameters were determined accordingly. The established Rankine cycle power block model was then coupled with the parameter optimization results to carry out a secondary optimization of the initial heliostat field. Through the above study, the aim is to realize a shift from single-objective geometric optimization of the heliostat field to comprehensive optimization oriented toward annual plant power generation performance and scenario adaptability, thereby providing a basis for scheme design and parameter selection of molten-salt tower solar thermal power plants. For external validation, the annual generation predicted for the Delingha 50 MW commercial plant was 142.15 GWh, corresponding to a relative deviation of 2.64% from the published design value of 146 GWh. This indicates that the coupled framework can reasonably capture the integrated response of the heliostat field, thermal storage system, and power block at the plant level. The model is therefore suitable for generation-oriented parameter screening and preliminary design of tower molten-salt CSP plants, while detailed component-level transient design still requires higher-fidelity engineering models. Full article

The article presents a comparative thermodynamic and economic analysis of nuclear power plants using high-temperature gas-cooled reactors (HTGRs) and small modular pressurized water reactors (SMRs). HTGRs, with their ability to achieve steam temperatures exceeding 650 °C, offer significantly higher electricity generation efficiency (approximately 52%) compared to SMRs and traditional PWRs, which achieve around 32%. The study underscores the importance of economic efficiency in investment decisions, noting that while SMRs are still in the conceptual phase, their future construction is uncertain, with realistic deployment expected by the late 2030s or early 2040s. The analysis highlights the superior thermodynamic performance of HTGRs due to their hierarchical dual-cycle gas–steam technology, compared to the single-cycle Clausius–Rankine process used in SMRs and PWRs. The paper contributes new insights into the comparative advantages and challenges of these nuclear technologies, particularly emphasizing the advanced safety features of HTGRs and the inherent design challenges associated with scaling down PWR technology for SMRs. Full article

This study quantifies the benefit of integrating machine learning (ML) with exergy analysis for automotive waste heat-to-power (WHP) systems. A PRISMA 2020 systematic review (2015–2025) across Scopus, ScienceDirect and Web of Science screened open-access peer-reviewed articles, yielding 19 eligible studies on organic Rankine cycle (ORC), thermoelectric generator (TEG) and hybrid ORC–TEG configurations. A random-effects meta-analysis shows a pooled moderate-to-strong gain (Hedges’ g = 0.49; 95% CI: 0.31–0.67) and a symmetric funnel plot. ORC–ANN optimization is strongest (g = 0.61), followed by hybrid CFD–ML (0.55). Multi-objective ML (0.52) and TEG models (0.34–0.41) improved performance, supporting improved recovery and reduced fuel use and CO₂ emissions. Full article

This study investigates the integration of Organic Rankine Cycle systems with hydrogen production and use to enhance energy efficiency and economic viability in waste heat recovery applications. A comprehensive thermodynamic, exergoeconomic, and environmental assessment evaluates multiple ORC configurations and six working fluids across hospital and hotel facilities. The analysis quantifies component-level exergy costs, system-level economics, and operational CO₂ emission reductions, focusing on optimal sizing strategies and threshold conditions under which hydrogen storage enhances energy autonomy without compromising economic viability. Results reveal fundamental design trade-offs: Basic ORC achieved the lowest LCOE at 0.033 $/kWh through operational simplicity, while complex configurations extract up to 70% more power at 14–32% higher cost. N-pentane exhibits superior thermodynamic–economic performance in the Parallel Dual ORC configuration, achieving 20% thermal efficiency and 40% exergy efficiency. R1233zd emerges as the preferred alternative from a safety perspective, exhibiting comparable performance with minimal penalties in both power generation and efficiency metrics. System-level analysis shows that properly sized ORC–hydrogen integration reduces Hospital 1 user LCOE_tot from 0.23 $/kWh to 0.069 $/kWh—a 70% reduction achieved by minimizing grid dependence. Environmental benefits strongly correlate with grid carbon intensity, with operational CO₂ emission reductions ranging from 181 tons annually in Spain to 752 tons in Poland. Full article

The efficient recovery of low-enthalpy geothermal resources $(T\le 150$ °C) faces significant thermodynamic limitations due to thermal mismatch in evaporators when pure fluids are utilized. This study investigates low-GWP zeotropic mixtures (Pentane/Isobutane), optimized using the NSGA-II algorithm, to enhance both the efficiency and operational resilience of Organic Rankine Cycles (ORCs). The isothermal behavior of conventional fluids limits exergy recovery and increases the Levelized Cost of Energy (LCOE). To address this, an advanced simulation tool, “ORC Master Suite”, was developed and validated against recent literature. Exergetic efficiency and LCOE were simultaneously optimized under strict Pinch Point constraints. Results show that the low-GWP zeotropic mixture of Pentane/Isobutane (70/30% w/w) achieves a 15–25% increase in exergetic efficiency compared to pure fluids, mainly due to the temperature glide, which reduces irreversibilities. Despite the increase in required heat transfer area and the strict capital expenditure penalties associated with ATEX safety protocols for highly flammable hydrocarbons, the LCOE remained competitive against the reference fluid. Overall, low-GWP zeotropic mixtures not only improve thermodynamic performance but also exhibit higher operational resilience to geothermal source fluctuations, making them a promising and sustainable alternative for future geothermal power plants. Full article

This article presents a performance assessment of an electrical power and cooling system powered by a parabolic dish collector and using refrigerants with low global warming potential. The study was conducted using energy and mass balances for each component and system. The simulation includes various parameters, such as solar radiation, the focal temperature of the solar collector, the ambient temperature, the power cycle pressure ratio, and the chiller’s evaporation temperature. The results show that the efficiency of the organic Rankine cycle with the refrigerant R1233zd(E) is similar to that of the refrigerants R123 and R245fa and is up to 11 and 50 times lower than with R290 and R744, respectively. The solar absorption chiller using the refrigerant R717 can achieve cooling with a supply temperature up to 5 °C lower than that of R718. The dynamic simulation results show that the energy efficiency of the proposed solar-powered generator–chiller is 14% higher than that of a standard solar-powered absorption chiller. Furthermore, the same solar-powered generator–chiller reduces the primary energy required by a conventional system by 60% (PESr = 0.60). The presented results may be useful for the design of sustainable generator–chillers for rural areas or for autonomous housing in tropical climates. Full article

Carnot batteries based on the coupling of high-temperature heat pumps (HTHPs) and Organic Rankine Cycles (ORCs) emerge as promising solutions for large-scale and long-duration energy storage, enabling sector coupling and the valorization of industrial waste heat. In such systems, the charging subsystem plays a dominant role, as variations in heat pump performance influence the round-trip efficiency more strongly than comparable variations in the ORC. This work presents a thermodynamic assessment of Rankine-based HP–ORC Carnot batteries focusing on the influence of heat pump configuration and working fluid selection. System performance is evaluated using the heat pump coefficient of performance, volumetric heat capacity, ORC efficiency, and Carnot battery round-trip efficiency through a grid-search optimization over a wide range of storage outlet and waste heat source temperatures. The results show that single-stage configurations are optimal at low to moderate temperature lifts, while two-stage and cascade systems become advantageous at higher lifts. Among the investigated fluids, R-601 provides the highest round-trip efficiencies at elevated storage temperatures, whereas R-600 enables more compact systems due to its higher volumetric heat capacity. These findings provide design guidance for selecting heat pump configurations and working fluids in industrial waste-heat-assisted Carnot battery applications. Full article

This study develops and optimizes a hybrid plant that couples a recompression sCO₂ Brayton cycle to a central-tower particle receiver with a bottoming Organic Rankine Cycle (ORC), including environmental and exergy balances. The two scenarios revealed Pareto points that raised the exergy efficiency to 0.65 in winter and reduced the fuel flow to 15 kg/s. Scenario number two achieves an overall thermal efficiency of 0.50 with total daily emissions of 2520 t CO₂ and 2850 kg NO_x, enabling nearly constant net power. Exergy destruction is concentrated in the high-temperature recuperator (HTR) and ORC turbines (27% each) and the ORC condenser (25%). Compared to a non-optimized baseline, the best solutions increased the ORC and Brayton efficiencies by 6.8–12.66% and 33.4–33.5%, respectively; cut gas-turbine power by 34% and ORC power to 10%; and lowered daily CO₂ and NO_x emissions by 52%. The gains stem from the coordinated adjustments of key levers: lower gas-turbine inlet temperature (about 10%), reduced Brayton mass flow (23%), and tuned ORC turbine inlet pressure. Full article

To enhance the aerodynamic performance of organic Rankine cycle (ORC) turbines under increasing energy demands, surrogate-based optimization was applied to a 100 kW ORC turbine rotor. Four representative surrogate models—a radial basis neural network (RBNN), Kriging, response surface approximation (RSA), and a PRESS-based weighted (PBW) ensemble—were comparatively evaluated under identical numerical conditions. Independent optimizations of the first- and second-stage rotors enabled an examination of how different design variable space characteristics influenced surrogate predictive behavior. A fractional factorial sampling strategy was used to construct the training dataset, and learning curve analysis was conducted to assess sample size adequacy. Sensitivity estimation revealed distinct response surface characteristics between stages, allowing the interpretation of variations in surrogate stability. In both stages, geometric modifications were primarily concentrated near the outlet blade angle, identified as a dominant variable influencing efficiency. CFD validation confirmed that surrogate-based exploration successfully identified improved rotor geometries. Flow-field analysis indicated reduced entropy generation near the trailing edge region, suggesting the mitigation of aerodynamic losses. The results demonstrate that surrogate-based optimization can reliably improve turbine performance within a bounded design space, while the relative effectiveness of surrogate models depends on the sensitivity structure of the underlying problem. Full article

The supercritical carbon dioxide (SCO₂) Brayton cycle presents a promising alternative to the traditional steam Rankine cycle, owing to its superior thermal efficiency, high power density, and compact design. As a key component governing system performance, the heat exchanger requires a highly compact and efficient design. This study proposes a novel additively manufactured (AM) wavy microchannel heat exchanger that achieves a compactness of 1670 m²/m³. The design incorporates adaptive flow channels to accommodate SCO₂’s density variation, along with wavy patterns and ribs to enhance thermal performance. A comprehensive fluid–thermal–mechanical coupling numerical analysis was conducted to evaluate its thermal–hydraulic and mechanical performance. Within the Reynolds number range of about 900–6000, the wavy structures improve the heat transfer rate by 21–58%, compared with the straight channel. The maximum effectiveness (ε = 0.66) occurs at a Reynolds number of 900. Compared with other heat exchangers used in the SCO₂ cycle, the overall performance of the hot and cold channels has improved by 12–44% and 3–89%, respectively. Structural analysis confirms that the average total stress under operating conditions remains below the yield strength of the Inconel 617 material, with thermal stress being the dominant contributor. This work underscores the potential of the proposed AM heat exchanger to deliver a superior combination of compactness, thermal–hydraulic performance, and structural integrity for advanced SCO₂ power cycles. Full article

The increasing regulatory pressure on the maritime sector to decarbonize, driven in part by market-based mechanisms at the European level, is accelerating the development of onboard carbon management and energy-efficiency solutions. In this context, this study evaluates an integrated architecture that combines a CO₂ liquefaction system with organic Rankine cycles. The system captures 66% of the total CO₂ emitted by ship engines and is capable of recovering up to 2600.8 kW of energy from onboard hot and cold sources. To identify the most suitable working fluids, an extensive screening of 208 low-GWP zeotropic mixtures is conducted, assessing their thermophysical behavior and energy recovery performance. A detailed thermo-economic assessment is undertaken, including the calculation of CO₂-equivalent savings, GHG abatement cost, and payback periods. To account for fuel price variability, probabilistic modelling based on Monte Carlo sampling is applied to estimate the distribution of discounted payback outcomes. The results demonstrate that Novec 649-based zeotropic mixtures combined with the proposed architecture reduce fuel consumption and enhance onboard CO₂ management while remaining safe and economically viable across a wide range of operating scenarios. Full article

This paper investigates an Organic Rankine Cycle (ORC) system for low-to-medium temperature heat recovery using comparative thermodynamic, exergoeconomic and economic modelling. A working-fluid study considering environmental and thermodynamic perspectives is conducted. A 20 kW ORC unit is tested and used as a feasibility and trend-consistency reference to support the modelling assumptions and practical operating bounds. A parametric study then examines the effects of evaporator pressure, condensation temperature, superheat, subcooling and heat-exchanger pinch-point temperature differences on net power output, first- and second-law efficiencies, total product cost and total capital investment under prescribed boundary conditions. Multi-objective optimization is applied to identify Pareto-optimal trade-offs and representative compromise solutions. Results show an intermediate evaporator pressure maximizes net power output, while lower condensation temperature generally improves efficiency; superheat has limited efficiency impact but should ensure safe operation, and a small subcooling margin (around 3 °C) mitigates cavitation risk. The best overall performance is obtained with an evaporator pinch of 3 °C and a condenser pinch of 5–9 °C; tightening pinch constraints increases required heat-transfer area and makes heat exchangers the main cost bottleneck for high-efficiency solutions. Full article