Abstract

Salt hydrate-based thermochemical heat storage is a crucial technology for long-term heat storage. Sodium phosphate stands out due to its high energy storage density, lower dehydration temperature, and low cost. However, its practical application is limited by issues such as deliquescence and agglomeration. In this study, expanded graphite, known for its high thermal conductivity and rich microstructure, was used as the primary matrix. Composites with mass contents of 80%, 60%, and 40% were prepared using the impregnation method. Hydration tests were conducted at 30 °C and RH 80% to examine the microstructure, thermal storage properties, and cycling stability of the pure salt and the composites. The results demonstrated that the incorporation of expanded graphite improved the adsorption kinetics of the composites and thermal conductivity mitigated the deliquescent agglomeration of pure salt, and reduced the dehydration temperature. EG80 has a maximum water absorption of 1.24 g/g, an energy storage density of 1081.8 kJ/kg and a thermal conductivity of 2.98 W/(m-K). After 10 storage discharge cycles, the thermal storage density remained above 1000 kJ/kg, indicating good stability.

Abstract

Sacrificial sodium-rich salts are promising pre-sodiation method to compensate the irreversible capacity of SIBs for energy density enhancement. To increase the capacity utilization ratio and decrease the decomposition potential, the particle size of sacrificial salts is generally reduced to lower than 10 um. However, large amounts of solvent are required to disperse the salts in slurry-coating electrodes, which increases the electrode production cost and limits the mass loading of electrode. This work utilizes dry-processing method to achieve sustainable and high-energy pre-sodiation cathode using Na2C2O4, which is free of using solvent and able to produce ultra-thick electrodes. The feasibility of Na2C2O4 as additive in ultra-thick dry-processing electrode has been demonstrated by electrochemical performance evaluation and electrode structure characterization. The full cells with pre-sodiation achieve large reversible capacity of 101.52 mAh g-1 at high areal capacity of 5.4 mAh cm-2 under 0.1 C as well as superior energy density of 309.3 Wh kg-1 and stable cycling. The novel electrode production strategy is promising for large-scale manufacturing of high-energy-density and low-cost SIBs.

Abstract

In recent years, the power industry has seen a significant uptick in renewable energy integration, including solar and wind farms, accompanied by energy storage systems. While this has increased overall generation capacity, it has also posed challenges to grid security and vulnerability. Key issues such as low short circuit ratios due to renewable integration and the retirement of synchronous machines have weakened grids. Grid forming inverters therefore have emerged as a vital solution, aiding solar and wind farms in maintaining stability during low short circuit ratio conditions. However, traditional Virtual Synchronous Generation (VSG) controllers, while beneficial, often introduce oscillations during disturbances, threatening network stability. This paper introduces an innovative approach that integrates Virtual Synchronous Generation Control with a Virtual Impedance Strategy to address stability challenges in solar and wind farms under low short circuit ratio conditions. By eliminating the need for Phase-Locked Loops (PLL), this method effectively mitigates oscillations during faults and voltage disturbances, thereby ensuring grid stability, with compliance to grid codes such as those of NER and AEMO Australia serving as guidelines. Implementation in PSCAD, which is widely used in the power system industry, validates its capability to meet stringent grid code requirements.

Abstract

In the present work, a simple numerical model is developed to estimate the performance of a solar flat plate collector (FPC) with water and CO2 as heat transfer fluids. An experimental test rig validates the model with water as heat transfer fluid (HTF). Though water is an excellent working fluid, it cannot be used in places where the ambient temperature falls below 0oC. Though antifreeze solutions can be added to water, this decreases the overall efficiency of the collector. In this context, using supercritical CO2 (s-CO2) in place of water can offer enhanced performance in addition to an extended operating temperature range. Hence in this study, the analysis is done with s-CO2 and water by considering four different cases under different operating conditions. The performance of both the HTFs is compared by using dimensionless quantities such as Reynolds number, Nusselt number, and Prandtl number. It has been observed that the outlet temperature and thermal efficiency of solar water heating system (SWHS) achieved are superior when the rate of mass flow is decreased, and the diameter of the riser tubes is made smaller. It has also been observed that substituting s-CO2 with water as the HTF in a solar FPC improves the overall performance. The solar collectors containing s-CO2 have high operating pressures, phase-changing potential with the change of ambient temperature, and considerable property variations around the critical point of the fluid, which are the major challenges for designing this type of SWHS. Thus, these subjects demand an extensive investigation.

Abstract

In recent years, Japanese companies and municipalities have increasingly recognized the importance of urban decarbonization. Urban areas, with their concentration of businesses, must consider not only decarbonization but also the well-being of the people working there. It is particularly important for business leaders to balance decarbonization efforts with employee well-being.
This project aims to create scenarios that achieve both decarbonization and well-being in Nihonbashi, a central business district in Tokyo.
The main focus is on long-term forecasting and management of energy demand using integrated simulation technology with an urban digital twin and developing scenarios that contribute to improving the overall well-being of employees.
Project activities include predicting and visualizing hourly energy demand for buildings within the area and assessing the effects of various decarbonization options. One decarbonization option involves implementing a system to transmit locally generated renewable energy to Nihonbashi and validating it with predictive models. By collaborating with building owners to advance energy management, the project has identified the potential to achieve approximately 10% energy savings.
In addition, the project will also work to improve employee well-being by implementing a chatbot program that will educate employees about their company’s decarbonization activities and encourage behavior change to increase their sense of contribution.
The project aims to enhance sustainable urban development and comfort in the office area and is an important step in a larger decarbonization initiative that will be implemented in partnership with building owners in the Nihonbashi area.
Ultimately, the project aims to improve energy efficiency and overall community well-being and serve as a model for future urban sustainability.

Abstract

The present study conducts a thermal analysis of a silica gel-based open cycle reactor serving as a daily heat storage system. Heat and mass transfer in the reactor during heat discharge are simulated using a transient local thermal non-equilibrium model. The model is validated against experimental data obtained under two different operating conditions, indicating satisfactory agreement between the experimental and the simulated results. Additionally, the study explores the space heating demand on the coldest winter day in London. Design criteria, including the optimal amount of silica gel and the required air flow rate for this open bed reactor to meet this demand, are evaluated and analysed.

Abstract

In the context of the accelerating global sustainable and low-carbon energy transition, maximizing the utilization of the cold energy value inherent in LNG holds significant importance for enhancing the competitiveness of corporate industrial chains and high-quality energy mitigation development. Given the diverse types, varying scales, and complex business cooperation models of LNG cold energy utilization, this research focuses on four major types: cold energy power generation, cold energy storage station, cold water aquaculture, and liquid air energy storage. By considering policy, methodology, and models, and taking into account economic, energy, and environmental factors, the study adhered to the principle of “seeking common ground while reserving differences, emphasizing key points”. Optimal techno-economic evaluation methods and key evaluation indicators were selected, and constructs energy substitution modules, carbon sink trading modules, and policy guarantee modules were built. An economic and “3E” comprehensive benefit evaluation method for LNG cold energy utilization project was formed, and suggestions for promoting the development of cold energy business from a technical and economic perspective were also provided. The research findings could promote the implementation of LNG cold energy utilization project, providing reliable references and insights to prevent the waste of cold energy resources

Abstract

Flow channel or flow field designs have a significant impact on the performance of a Proton Exchange Membrane Fuel Cell (PEMFC). These channels are essential for distributing reactant gases, eliminating byproducts like water, and managing heat within the cell. Enhancing the flow field design can improve the efficiency, power output, and overall lifespan of PEMFCs. A three-dimensional multiphysics, two-phase PEMFC model with novel ribs in the form of asymmetrical airfoil in a parallel flow channel has been investigated in the present study. The ribs are placed along the length of the channel equidistantly. With the operating parameters kept constant, effect of different types of ribs on the overall performance of the fuel cell is reported and compared with the Baseline case where no ribs are present. The present model comprises of a single unit PEMFC modelled in the commercial software package ANSYS Fluent version 2023R2. A comparative study on the effects of different ribs shapes like rectangular, circular and asymmetrical airfoil on the overall PEMFC performance is presented. The obstruction in the flow channel is observed to improve the polarization curve, i.e., current vs. voltage (I-V) curve as well as current vs. power (I-P) curve, in other words, the fuel cell performance. Pressure drop is found higher for parallel flow channel with rectangular ribs than baseline without ribs. Thus, this study examines how a different flow channel design with ribs affects PEMFC performance metrics, offering insights into how changes in flow field configuration can propel advancements in fuel cell technology.

Abstract

Extracting heat from a deep geothermal reservoir in a clean and efficient manner has always posed a significant challenge in geothermal exploration. This paper presents a numerical study of the heat extraction performance of a perfect super-long gravity heat pipe (SLGHP) under the assumptions of either an infinitely large heat transfer coefficient inside the SLGHP or a constant phase change temperature throughout the SLGHP. As the phase transition temperature of the working fluid in the pipe may be higher than the temperature of the surrounding formation, it is necessary to eliminate the possibility of heat loss at the top of the SLGHP by setting it to zero or providing a fully thermally insulated boundary. The results show that the heat output and heat output per unit wellbore length increase linearly with well depth, and the greater the given geothermal gradient and formation thermal conductivity, the larger the heat output and heat output per unit wellbore length

Abstract

Indoor air quality is an important factor which affects the cognitive ability and performance of the occupants of a building, hence, fresh air is incorporated into indoor spaces. However, due to high ambient temperatures, typically in tropical zones, will further increase the energy consumption of HVAC systems. Phase change materials (PCM) are widely employed due to their high energy storage capacity as well as keeping the operating temperature unchanged. The study explores the effect of using a PCM-based heat exchanger for reducing the fresh air temperature and, hence reducing the fresh air ventilation load of a building. On using octadecane as PCM, the study observed that for 8 hours of operation, the average temperature reduction in the air for no fins is 1.80 °C, which increases marginally to 1.82 °C for 1% CuO and 4.15 °C on using 24 longitudinal fins. It leads to an energy saving of 3.51%, 3.83% and 7.75% over a conventional HVAC system for a system with no fin, 1% CuO, and 24 fins, respectively. Further, PCM is charged using exhaust air, and PCM solidifies completely in 4 hours. The study provides an energy-efficient solution for the sustainable use of HVAC systems for policy makers and HVAC engineers.