Abstract

To investigate the phase transitions during adsorption and kinetics of vapor adsorption on mesoporous silica, a series of molecular simulations are conducted in this work. The results provide new insights into the formation of liquid bridges and the growth of cavitation bubbles. The liquid is in a metastable state during desorption, with evaporation potentially occurring through meniscus retreat or cavitation. Spontaneous formation of tiny bubbles is observed in the liquid phase. multiple tiny bubbles often form in proximity, indicating their interdependence. Eventually, as evaporation continues to increase, these bubbles coalesces into ones, initiating the nucleation mechanism for the liquid-to-vapor transition of a metastable liquid.

Abstract

Wind power is a significant part of renewable energy and plays a crucial role in modern power networks. Precise wind power prediction is essential for grid scheduling. Numerous studies have been undertaken to forecast wind energy. The traditional single prediction model is limited as it fails to consider the complexity of meteorological data, specifically the correlation between meteorological data and wind energy. Additionally, it overlooks the volatility of wind power. As a result, there is a decrease in prediction accuracy. This study introduces a novel model for prediction short-term wind power combinations, incorporating meteorological feature selection and signal decomposition to overcome current model constraints. Firstly, maximal information coefficient (MIC) is used for meteorological feature selection. Secondly, for the volatility of wind power, complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) is used to decompose the wind power time series data. Subsequently, the meteorological data that underwent feature selection, along with the two frequency signals, were fed into the sample convolution and interaction network (SCINet), bidirectional long short-term memory (BiLSTM), and gated recurrent unit (GRU) models via three separate channels for prediction. The weight coefficients for the meteorological data prediction results and the signal decomposition prediction results were determined using sequential least squares programming (SLSQP). These weight coefficients were then used to get the final prediction results through a weighted combination. The experimental results show that the prediction accuracy of the model proposed in this study is significantly improved compared to the traditional single prediction model.

Abstract

Mitigation pathways are critical in achieving carbon neutrality. However, there is still uncertainty about the potential of these technologies. Therefore, it is necessary to develop possible scenarios for such technologies to facilitate forward-looking decision-making in national energy strategies. In this study, Japan’s energy dynamics from 2010 to 2050 are examined, focusing on shifts from fossil fuels to sustainable sources within a declining population and expanding economy context. Utilizing the Glocal Century Energy Environment Planning (G-CEEP) model, Various scenarios for Japan’s future energy system to achieve net-zero CO2 emissions by 2050 were examined. This transition suggests profound impacts on national energy policies and economic strategies, supporting Japan’s commitment to sustainable development and environmental stewardship. This research contributes to understanding the integration of energy policy with macroeconomic and environmental objectives in a transitioning economy.

Abstract

Research on Proton exchange membrane fuel cell (PEMFC) bulldozers is currently in its infancy. Performing crucial investgation of fuel cell operation characteristics and potential faults based on the bulldozer operating conditions is beneficial for the promotion of fuel cell applications. In this work, with a 110 kW PEMFC and a 90 kW battery used as the power system for the bulldozer. The contents are threefold. Firstly, a numerical model integrating the bulldozer, cabin, motor and power system is established, and the accuracy and reliability of the model is evaluated. After that, based on the operating conditions of bulldozer including no-load, soil-cutting, soil-transportation and unloading soil stage, the operation characteristics of the fuel cell system are analyzed. To detailed analyze the variation patterns of the various parameters inside the fuel cell under the aforementioned operating conditions, a three-dimensional numerical model of fuel cell is established. The results indicate that PEMFC power and current density rapidly increase to 110 kW and 1.513 A/cm² during the soil-cutting phase, and then decrease rapidly to 50 kW and 0.551 A/cm² during the unloading soil phase, showing significant rate of change. The PEMFC stack temperature can reach a maximum of 346 K. The average liquid saturation in gas diffusion layer reaches a maximum of 0.30 at the end of the soil-transport phase, and the uneven distribution of internal liquid is significant. There is significant uneven distribution of liquid, which could lead to localized flooding issues at the end of soil-transport. Appropriate strategies need to be implemented to control.

Abstract

The efficiency of proton exchange membrane fuel cells (PEMFC) is influenced by both the components of the membrane electrode assembly (MEA) and the fabrication process of the MEA, which in turn impacts the characteristics and structure of the electrode. This study examines the impact of hot-pressing temperatures on the gas diffusion layer (GDL) and catalyst-coated membrane (CCM). Proper hot-pressing is essential for optimizing performance. The ideal hot-pressing temperature identified is 100 ℃, resulting in a maximum power density of 1.228 W/cm2 for the MEA, representing a 4.9% improvement compared to MEAs without hot-pressing. While hot-pressing does increase the ohmic resistance of the MEA across all humidity levels, appropriate hot-pressing temperatures can notably enhance the electrochemical surface area (ECSA) by 16.3% and reduce charge transfer resistance. Additionally, mass transfer resistance can be minimized, potentially due to the narrowing of the interface gap between the catalyst layer (CL) and GDL. These findings offer valuable insights for MEA fabrication processes and can serve as a valuable resource for practical applications.

Abstract

Unconventional oil and gas resources, such as shale oil and gas, are gradually attracting great attention from all of the world. Horizontal drilling and large-scale hydraulic fracturing technology are used to efficiently extract oil from shale formation. A high long-term conductivity is essential for hydraulic fracturing, so accurate evaluation of propped fracture conductivity is of great significance for the development of shale reservoirs. In this paper, FCMS-V fracture conductivity system, scanning electron microscope and sieve analysis were used to study the influence of various factors on fracture conductivity, proppant crushing and embedment under reservoir conditions of the DG shale formation in Songliao basin. A visual study of proppant embedment into the shale rock was carried out. The effects of granule size, granulometric composition, concentration of proppants and closure pressure on fracture conductivity were revealed. It was found that due to the embedment of proppants, the long-term conductivity decreases by 10.2%. After exposure to a closure pressure of 30 MPa, the degree of crushing of the 30/50, 40/70 and 70/140 mesh proppants are 56.9, 38.8 and 26.7%. The findings from this experimental study could help hydraulic fracturing design for long term production of shale reservoirs.

Abstract

Hydrogen storage systems and, specifically, metal hydride-based systems, hold a significant potential when it comes to finding safe, affordable, and efficient energy storage solutions [1-3]. A challenge often associated with most metal hydride compounds is building an efficient Heat Management System to prevent the hydride temperature to diverge from equilibrium and, thus, slow down the storage process [4]. We analyze a hybrid Metal Hydride – Phase Change Material (MH-PCM) configuration, where the PCM surrounds the MH powder and works as Thermal Storage Unit (TSU). During desorption of hydrogen (endothermic), the PCM provides heat to the MH by using the same energy that it had previously stored during the absorption stage (exothermic) [5]. However, PCMs suffer from low thermal
conductivities, thus several Thermal Augmentation Systems (TAS) might be employed to try and solve this issue. Among them, we focus our attention on the addition of Expanded Natural Graphite (ENG) into the PCM. ENG has a high thermal conductivity and can be easily mixed within the PCM to form a composite. The reduction in gravimetric and volumetric density is a negative side effect of using ENG.
In this work, we numerically assess the impact of ENG by comparing the absorption and desorption processes of a baseline MH-PCM design and other layouts with increasing amounts of ENG.
The results show that the overall cycle time is reduced by 20.9% when increasing the ENG volume fraction from 0% to 25%. The gravimetric density drops by 12.3%, thus suggesting the increase in the storage system weight and size. The average inlet and outlet power increase from 2.7 kW to 3.6 kW and from 1.2 kW to 1.45 kW, respectively.

Abstract

The non-uniform distribution of building surface temperatures caused by building shading significantly affects the airflow structure within the building complex. However, previous numerical studies have mostly ignored the non-uniform distribution of building surface temperatures, instead using uniformly heated surfaces as an equivalent substitution. This approach compromises the accuracy of wind-thermal environment predictions within the building complex. Therefore, this study focused on a 4×4 dot-formed building complex and employed numerical simulation methods to explore the impact of the uniform surface assumption on the airflow structure within the complex. The airflow structure and the recirculation ratio rate were used as quantitative indicators in this analysis. The results indicated that the assumption of uniform surface introduced errors in predicting the risk of thermal accumulation within the building complex, and the errors increased with the increase of temperature difference. When the temperature difference was 10K, assuming a non-uniform surface as a uniform surface caused a change in the vortex structure of the airflow, leading to an error in predicting the airflow direction and overestimating the recirculation ratio by 23.74%. The research results emphasized the significance of considering the non-uniform surface temperatures caused by building shading for accurately predicting the wind-thermal environment of the building complex and further reducing energy consumption.

Abstract

In this paper, a series of evaporation experiments were carried out on a cylindrical pool. From these experimental results, we obtain the axial temperature distribution of the ethanol evaporation process, and compare the results of different heating temperatures at different depths. We found that the evaporation of ethanol of different depths will bring different flow patterns, thus changing the temperature distribution. At the same time, we also determined the temperature jump range of ethanol evaporation in cylindrical pool heated by bottom.

Abstract

Microplastics (MPs), produced in large quantities due to their affordability and durability, have raised concerns about their environmental impact. In 2021, global plastic production reached 390.7 million tons. Cold seeps harbor significant populations of ANME-1 archaea, which are involved in methane production and oxidation. However, the effect of MPs on the gene abundance related to methane metabolism in ANME-1 remains unclear. To address this gap, the present study conducted laboratory cultivation experiments using sediment and seawater samples from the Haima cold seep. The main findings are: (1) The addition of MPs did not significantly affect the gene abundance of the ANME-1 community (p > 0.05). (2) Methane metabolism gene coverage in sediment was higher than in seawater (p < 0.001). (3) Environmental factors significantly impacted the gene abundance of nitrogen and methane metabolisms in seawater compared to sediment. This work provides a better perspective on the impact of MPs on methane production and oxidation in the cold seep.