Energy Conversion and Management-X最新文献

The thermo-hydraulic effects of the number and placement of holes in rectangular winglet vortex generators on a solar air heater were investigated numerically. This study examined airflows under conditions where the Reynolds number ranged from 3000 to 20,000 and the Prandtl number was 7.070. Variations in the number of holes, ranging from one to nine, resulted in ten different hole-arrangement patterns. The blockage ratio, which is defined as the ratio between the surface area of the vortex generator and the cross-sectional area of the airflow duct, remained constant throughout the investigation, which made it necessary to vary the hole diameters. For the simulations, the Realizable k-epsilon model supplemented with a wall function was employed. The results indicated that the number of holes had a significant effect on the Nusselt number, and the winglet vortex generator featuring a single hole was observed to have the highest averaged Nusselt number, whereas the nine-hole configuration had the lowest. Conversely, the impact on the friction factor was comparatively minimal. Additionally, an analysis of the hole placement revealed slight variations in the averaged Nusselt numbers and friction factors when the number of holes remained constant. Velocity plots and pathlines were utilized to elucidate the flow structures and induced vortices. This study concludes that large and well-organized vortices were more efficient for heat transfer under the experimental conditions. In addition, maintaining a constant blockage ratio between the vortex generator’s surface area and the airflow duct’s cross-sectional area in the solar air heater contributed to the friction factor being mostly unaffected by the number of holes.

Enhancing the efficiency of low-cost solar-powered desalination technologies, such as solar stills (SS), is essential for ensuring continuous access to freshwater in remote, water-stressed areas, particularly during cloudy or rainy days when the performance of conventional SS systems is compromised. This study introduces an innovative stepped solar still design, optimized for ease of operation, maintenance, environmental compatibility, and improved efficiency, especially under low-light conditions. The impact of the inlet mass flow rate on the desalination process was investigated to enhance distilled water production. Light absorption and step hot spot temperatures were further improved by incorporating natural and cost-effective absorbers, such as carbon, and an innovative soil-carbon combination. The synergy of this soil-carbon combination, enhancing light absorption, heat transfer, and storage through increased surface contact during radiation exposure and its distribution during shutdown, led to a 12.8% and 3% increase in distilled water production over the 4-hour test duration, compared to the baseline and carbon-only tests, respectively. This innovative design, combined with the use of a soil and carbon mixture, significantly improves the performance of solar distillation systems. These findings contribute to the development of sustainable, low-cost, and energy-efficient solutions for freshwater provision in remote areas, addressing both water scarcity and energy conservation challenges.

Solar photovoltaic (PV) power plants’ performance is severely impacted by multi-level irradiances or partial shading, leading to power losses and voltage instability. Also, partial shading adds further complexity to the maximum power point tracking algorithms by introducing numerous peaks in the power curves, resulting in additional losses. Numerous solutions are presented to deal with shading losses, and dynamic reconfiguration is the most effective; however, higher switch count and complex architecture make it impractical in real-world implementation. Hence, this study proposes a low-complexity architecture based on the grouped string voltage balancing approach. This approach utilizes a voltage balancing converter connected to groups of strings to enhance the power output of the array of PV plants, maintain overall system voltage stability, and eliminate the possibility of multiple peaks formation in the power curves. The effectiveness of the proposed approach is tested under numerous static and dynamic partial shadings and analyzed using power curves, power output, losses, efficiencies, and voltage stability. The validation is done by comparing the proposed approach with conventional and advanced architectures for a 32.5 kW system. The results show that the proposed method requires a 50 % reduced switch count than existing techniques, achieves 99.54 % efficiency, and maintains an average voltage stability of 0.01.

In heat pumps, the use of refrigerants with a low global warming potential (GWP) gains importance due to increasingly strict regulations regarding their ecological impact. In this regard, hydrocarbons (HCs), hydrofluoroolefins (HFOs), and their mixtures are the most promising options due to their thermodynamic properties. Besides the impact of the refrigerant, the cycle configuration (e.g., basic cycle and internal heat exchanger cycle) strongly influences the efficiency of the heat pump. While the potential of low-GWP refrigerants in internal heat exchanger (IHX) cycle configurations is widely investigated in numerical studies, there is a lack of experimental validation. Therefore, this work experimentally evaluates four HCs (R290, R600a, R436A, R1270) and the HFO R1234yf in comparison to R134a in a brine-water heat pump test bench. The test bench design allows to switch between the basic and IHX cycle, thus, enabling the simultaneous impact evaluation of the cycle configuration and the refrigerant on the performance. In the experiments, R1270 shows the highest efficiency for all operating points followed by R290 in the basic cycle. The IHX cycle improves the efficiency for all refrigerants in comparison to the basic cycle. The zeotropic mixture R436A achieves the highest efficiency improvements of up to 27.5% compared to the basic cycle, whereas the efficiency of the single-component refrigerants increases by 10% on average. Despite the significantly higher improvements of R436A due to the IHX, R1270 still leads to the highest coefficient of performance (COP) of up to 6.6 (B12/W35) in the IHX cycle configuration.

The growing concern about environmental degradation and the depletion of fossil fuel supplies has prompted experts to investigate alternate and sustainable transportation energy sources. In these circumstances, biodiesel made from renewable feedstock has emerged as a viable environmentally friendly alternative to conventional diesel. This study thoroughly examines the performance and emission characteristics of a 4-stroke diesel engine running on biodiesel blends, including reduced graphene oxide (rGO) nanomaterial. The non-edible biodiesel from the Jatropha curcas plant is utilized, and it is blended in various ratios with conventional diesel, ethanol, and nanomaterial rGO to improve performance and emissions parameters. Torque increased by up to 17 % in rGO DJE02GO25 at 3500 rpm, while Brake Power decreased by 6.3 % in rGO DJE01GO25 at 2600 rpm. Brake Thermal Efficiency decreased by 12.5 % in rGO Blend 1 at 2600 rpm, and Brake-specific fuel consumption decreased by 16.5 % in rGO DJE02GO25 at 3500 rpm. CO₂ emissions decreased up to 19.71 % in rGO Blend 10 at 2600 rpm. HC emissions decreased to 94 % in rGO blend 8 at 3500 rpm. Finally, NOx emissions decreased up to 84.78 % in rGO Blend 1 at 2900 rpm. The current study reveals that after adding rGO nanomaterial in biodiesel, there is a significant decrease in NOx and HC emissions.

Investigating the impact of dye compounds on cell performance is crucial for advancing dye-sensitized solar cells (DSSCs). This research focuses on the sensitivity analysis of the effect of critical parameters to enhance DSSC efficiency using a thermo-electric numerical model. These parameters include dye types, trapping parameters, diffusion coefficients, and photoanode thickness. When the type of dye changes, in fact, both physical and chemical properties (molar absorption coefficient, etc.) Change, but to avoid the complexity of solving the equations and only to evaluate the effect of the absorption wavelength range on the cell performance only changes in physical properties are considered. The model calculates steady and transient currents under actual weather conditions and sunlight. It incorporates time/space-dependent relationships for increased accuracy and examines electron, iodide, and triiodide ion interactions under varying environmental conditions. Key concepts include the quasi-Fermi level and the multiple trap model, assuming that trapping processes are faster than electron transport and recombination. The results showed that increasing the trapping parameter can affect the transient current behavior, also increasing the thickness of the photoanode and the wavelength range of the dye increases the efficiency of the cell, so that the N749-BD provides the best performance. The findings provide insights into current–voltage characteristics, electron production, and the effects of photoanode thickness and dye types on cell performance, offering pathways for optimizing DSSC technology.

Battery energy storage systems can produce very fast bi-directional power flows, which makes them suitable for providing wind power regulation and frequency control services. Though battery systems can provide fast regulation services, their energy storage capacities are quite low in comparison to other generation sources, so regulation responses from them should be optimized to maximize availability of service. This paper proposes an aggregator that optimizes frequency control responses from battery energy storage systems to maximize service availability. The frequency control response from the aggregated system is defined by a single frequency-droop characteristic. This provides the predictability of response required to comply with grid codes and allows the aggregated system to participate in frequency control markets as a single entity. The method of implementation is fail-safe as failure to receive an optimized order from the aggregator does not prevent the battery energy storage systems from responding to frequency events. This mitigates stability concerns relating to communication delays between the aggregator and battery energy storage systems. Battery systems that provide multiple functions, such as frequency control system services and wind power regulation, can participate in the aggregator scheme by assigning a proportion of the battery’s capacity to the aggregator scheme. Simulations performed in DIgSILENT PowerFactory show that the aggregator successfully extends the duration of full regulation service from the battery systems during frequency excursion events.

The global growth of urban areas is unstoppable, and this growth is accompanied by an intensification of urban heat island effects, exacerbating the challenges of climate change and sustainable urban development in warm climates. In this context, understanding the intricate dynamics of these phenomena and their implications on the thermal behaviour of buildings becomes paramount. This study focuses on València, a Spanish city characterized by a Mediterranean climate, where the interplay between ground temperature variations, vegetation levels, and the thermal demands of buildings is investigated.

Land surface temperature measurements derived from satellite data, specifically from the Landsat-8 mission, provide a valuable lens through which to assess the heat island effect. These measurements are harmonized with data collected from local weather stations to establish a robust foundation for evaluating the thermal dynamics of the urban environment. European standards, coupled with Geographic Information System technologies, enable the simulation of temperature variations, and facilitate a nuanced analysis of their impact on the thermal demands of a building.

Moreover, recognizing the crucial role played by the urban climate in the influencing of heating and cooling needs, this study explores nature-based solutions implemented in València. By leveraging satellite-derived temperature and vegetation data over an extended period, it is possible to identify actions and elements that contribute positively to mitigating UHI effects and improving the overall climatic conditions. Results indicate that vegetation has a notable impact on local temperature, with distinct patterns observed in different seasons. The research incorporated the simulation of climate scenarios, introducing varying levels of vegetation. Results demonstrated a substantial reduction in cooling demand, particularly during the summer months. Buildings with a lower exterior surface-to-volume ratio exhibited a more pronounced reduction in energy consumption.

Nowadays, many sophisticated tools based on various mathematical approaches are used to support planning and strategic decision-making. In the field of waste management, allocation and location problems based mainly on the structure network flow problem are used with respect to infrastructure planning. Modern formulations of the problem allow the inclusion of integer and nonlinear constraints that reflect real-world operations. However, despite the advanced computational technology, such real-world problems are difficult to solve in adequate detail due to the large scale of the problem. Thus, the links in the system are simplified, but most often a transport network is aggregated. The individual nodes in the system may then represent areas with tens or hundreds of thousands of inhabitants, which does not provide sufficient insight for location tasks. This paper presents an approach to dynamically reduce the network with respect to selected points of interest. The selected areas are modeled in greater detail, while with increasing distance the entities are more aggregated into larger units. The approach is based on a transformation of the original network and subsequent cluster analysis, preferably using existing transport infrastructure. The presented approach provides the possibility of practical application of complex tools that are currently mostly theoretical due to high computational demands. The methodology is applied to a case study of Waste-to-Energy infrastructure planning, which needs to model a large area to fill a large capacity facility.