Abstract

The hydrogen-based microgrid is an excellent solution to address the issue of curtailment caused by the intermittency of renewable energy sources. In such a system, the energy management system plays a crucial role in determining the operational status of the microgrid. To effectively verify the energy management strategies, a hydrogen-based microgrid test bench has been developed, which mainly includes photovoltaic (PV) panels, a programmable direct current (DC) power supply, loads, a lead-acid battery, and a hydrogen storage system. The lead-acid battery is directly connected to a DC bus, primarily serving as short-term storage to address instantaneous power imbalances and maintain bus voltage stability. The hydrogen storage system includes a PEM water electrolysis (PEMWE) system, metal hydride tank, and a PEM fuel cell (PEMFC) system, serving as long-term storage for seasonal energy storage. Considering that the level of hydrogen (LOH) is crucial parameter for the energy management strategy, an LOH estimator, which is used to estimate the hydrogen capacity in the metal hydride tank, has been proposed. This study aims to bridge the gap between simulation and practical application, providing valuable insights and tools for the development of hydrogen-based microgrid system.

Abstract

The air supply subsystem is critical for proton exchange membrane fuel cells, determining the output performance of the stack. By controlling the speed of the air compressor and the opening of the back pressure valve, it is possible to achieve appropriate regulation of air supply pressure and mass flow rate. However, this process presents challenges due to disturbances and the coupling of multiple variables. This study employs the model predictive control algorithm to address these issues because of its strong decoupling capabilities and robustness. Initially, an M-sequence is designed to identify the system and obtain the predictive model for the MPC. Based on feedback output, a Kalman filter is then used to estimate the optimal unmeasurable state information. Subsequently, the MPC controller is designed to obtain the optimal control output under various constraints. Finally, by using a traditional PID controller as a control group, the performance of the proposed MPC controller based on Kalman state estimation is analyzed under current step change conditions.

Abstract

CO₂ gravity flooding is an effective method to enhance oil recovery by gas flooding. In order to clarify the synergistic effect degree of gravity differentiation and oil-gas mixing relative to EOR in the process of CO₂ gravity flooding and the oil displacement mechanism, physical simulation experiments were carried out to compare and analyze the differences of different displacement processes through microscopic visualization experiments, and to clarify the microscopic application rules. Through nuclear magnetic resonance (NMR) on-line displacement experiment, the contribution ratio of extraction degree in each level of pore throat was quantitatively divided, the lower limit of critical utilization of pore throat was defined, and the synergistic development effect was evaluated. The results show that miscibility and gravity differentiation can play a synergistic role at the same time to achieve the highest recovery rate (79.08%). Compared with immiscible horizontal CO₂ flooding, oil-gas miscible effect can reduce interfacial tension, delay gas breakthrough (0.68 PV to 0.79 PV), and lower the critical pore utilization limit (0.09 μm to 0.015 μm). The degree of utilization of pore throat under 0.1 μm was increased from 3.08% to 19.79%; Gravity differentiation can improve the transverse sweep effect during the oil and gas miscible zone moving down the displacement direction. At the same time, gravity flooding can improve the utilization degree of CO₂ on small pores by increasing the injection and production pressure difference.

Abstract

To ensure the safety of fuel cell vehicles and enhance overall vehicle performance, comprehensive thermal management is essential. Currently, thermal management for fuel cell vehicles mainly focuses on low-temperature environments, with relatively little research on high-temperature conditions. This paper proposes an integrated vehicle thermal management solution that includes thermal management for the fuel cell, lithium-ion battery, motor, and cabin. Additionally, a vehicle thermal management system model is built and the control strategies for high-temperature conditions are developed. Model predictive control algorithm is designed to settle down the air conditioning system cooling both the cabin and the lithium-ion battery in high-temperature environments. Simulation results demonstrate that this comprehensive thermal management solution exhibits excellent temperature control capabilities under extreme high-temperature conditions with lithium-ion battery response time of 2324s and cabin response time of 60.13s. And lithium-ion battery temperature is robust to variations of cabin temperature. Additionally, the temperatures of the fuel cell and motor are effectively controlled within the reference range.

Abstract

In this study, a low-carbon solar water heating system integrated with salt hydrates as storage mediums was developed. The thermal performance of the heating system was tested using a full-scale experimental platform. A performance comparison was conducted between the system using sodium acetate trihydrate (SAT)-acetamide (AC) and one using SAT. The heating system incorporating the SAT-AC (phase-change temperature: 47.8 °C) showed an approximate 5.3% increase in the coefficient of performance compared to the system using SAT (phase-change temperature: 56 °C). Additionally, the discharging time for the SAT-AC unit was extended, benefiting from its optimal phase-change temperature. These findings indicate the promising potential of the selected salt hydrates for solar water heating applications and provide valuable guidelines for designing efficient heating systems.

Abstract

Asphalt particles have the characteristics of high temperature resistance, salt resistance, good stability, oil affinity, and blocking water without blocking oil. They can effectively plug large pores in high temperature and high reservoirs with salt medium and low permeability. At present, there are few studies on the micro-displacement experiment of asphalt particle system. In this paper, the micro-fluidic experiment technology is used to carry out the oil displacement experiment of asphalt particles under the condition of high temperature in the reservoir. The migration and accumulation law of asphalt particles is described, and then the mechanism of asphalt particles is analyzed, and the effect of displacement is quantitatively analyzed. The experiment shows that the asphalt particles enter the water flow channel after injection, and gather at the inlet of the model and the narrow pore throat in the form of a bridge, and self-similar aggregation occurs. The originally dispersed asphalt particles tend to gather and change the distribution of remaining oil. The accumulation effect causes the channel to block, the corresponding channel seepage resistance increases, the system flow range is reduced, the seepage velocity is accelerated, and the injection system passes through the cluster and porous remaining oil, which expands the affected area and also makes the cluster and porous remaining oil become film-like or drip-like remaining oil, increasing the overall recovery degree. Quantitative analysis of the microscopic model with pore throat radius of 40um and 75um shows that for the 40um model, when the asphalt particle injection concentration is 1.0%, the initial water flooding cluster residual oil accounts for 85%, the asphalt particle displacement cluster residual oil accounts for 80.5%, and the subsequent water flooding cluster residual oil accounts for 75%, and the overall recovery degree increases by 8.13%. For the 75um pore throat model, when the injection concentration is 2.5%, the proportion of the remaining oil in the initial water flooding cluster is 60%, the proportion of the remaining oil after the displacement of the asphalt particles is 47%, and the proportion of the remaining oil in the subsequent water flooding cluster is 43.5%, and the recovery degree is increased by 7.02%.

Abstract

The enhanced vapor injection system (EVIS) has received considerable attention for its energy efficiency. In this paper, the EVIS is in-depth studied theoretically and numerically. First, the EVIS is equated to two cascaded single-stage systems. Then, the expression of the EVIS COP as a function of the intermediate temperature is obtained and numerically analyzed based on a new assumption of thermal perfection. The results show that there is not always an optimal intermediate temperature for the EVIS. Under different compressor isentropic efficiencies, the EVIS performance shows four different trends with the intermediate temperature. This finding will be of great value for the design and maintenance of EVIS and all types of two-stage compression systems.

Abstract

The flow channel structure relates to the flow channel and PTL contact resistance and mass transfer performance in the channel, especially at larger operating voltage, the gas transfer and ohmic loss seriously affect the Proton Exchange Membrane water electrolysis performance. In this paper, the flow channel sub-rib microstructure is designed, and the effects of different sub-rib microstructure designs on the performance of the electrolysis are compared by means of experiments and simulations, and the distributions of micro-vertebrae under the rib of the flow channel and liquid water in the channel, ohmic losses and mass transfer efficiency are analyzed to obtain the optimal design of the flow channel microstructure. The experimental results show that the 0.03 mm tabs under the rib can effectively reduce the interfacial ohmic resistance and improve the mass transfer, and the experimental performance is improved by 9.98% relative to the conventional flow channel, while the simulation results in a performance improvement of 14.30%.

Abstract

Anaerobic digestion coupled with microbial electrolytic cell (AD-MEC) is a promising method for waste energy conversion. However, the technology is currently stuck in a bottleneck. The optimization of the electrode structure is a prospective way to improve the methane production efficiency of AD-MEC. In this study, a new composite electrode structure applied in AD-MEC is developed, consisting of stainless steel wire mesh and carbon felt connection combined to form an electrode, and the two electrodes are connected by an insulating cloth to form a composite electrode plate. The composite electrode plate was applied to the AD-MEC reactor and the traditional AD reactor for comparative experiments. The results show that, the biogas production of the AD-MEC reactor increased by 76.6% compared to the control reactor at a voltage of 0.7V. In addition, the start-up time of the AD-MEC reactor was significantly reduced, the average daily methane content increased by 13.5%, and the cumulative methane production increased by 105.6%. Meanwhile, there are certain differences in microbial community richness and diversity between AD-MEC reactor and control reactor, which is considered to be one of the reasons for the improvement of methane production efficiency. The increase of biogas production and methane content demonstrates that the structural optimization of stainless steel wire mesh carbon felt composite electrode is an effective method to improve AD-MEC efficiency, waste treatment and energy recovery.

Abstract

Safety analysis is an essential tool for ensuring the economic and stable operation of integrated energy systems and is a crucial component of the energy management system. Given that the security region of tightly coupled electric-gas-heat integrated energy systems has not been extensively studied, this paper establishes the security region model and the total energy supply capability model for the integrated energy system. It discusses and analyzes the total energy supply capability and security region characteristics of the tightly coupled electric-gas-heat integrated energy system, highlighting the impact of coupling nodes on the thermal system’s heating capacity and the relationship between the total energy supply capability and load size.