Energy Science & Engineering最新文献

Efficient and reliable utilization of renewable energy at the user's end is the key to achieving a low-carbon life. This paper proposed a new distributed energy system around the comprehensive utilization of solar energy by integrating solid oxide fuel cell (SOFC), energy storage equipment, photovoltaic thermal (PVT) collector, and heat pump. By integrating the use of SOFC and PVT, we can further minimize reliance on fossil fuels, while employing the coupling of PVT and heat pump effectively mitigates the inherent challenges of solar energy's variability and intermittency, all while enhancing overall system efficiency. On this basis, we apply the heat current method to construct a cross-scale heat current model of the components and the system by considering the energy transfer, conversion, and storage characteristics of the system. By employing this model, we simulate the system's operation throughout an entire typical day, assess the COP enhancement of the PVT-coupled heat pump system, analyze the influence of diverse operating conditions on daily system performance, and evaluate the economy of the energy storage devices in the system.

To study the effect of vertical stress difference coefficient on fracture characteristics of shale fracturing, high stress true triaxial hydraulic fracturing test was carried out. By analyzing the profile after fracturing, it was found that the area of hydraulic fracture increased with the increase of vertical stress difference coefficient, and the probability of shear fracture will increase when the stress difference coefficient was high. A high vertical stress differential coefficient exerts a strong control over the direction of crack propagation, while a low vertical stress difference coefficient is beneficial to improve the roughness of hydraulic fracture surface and promote the formation of complex fracture network. By analyzing the pump pressure curves of different tests, it was found that with the increase of vertical stress difference coefficient, the formation and expansion of hydraulic fractures were more difficult. The surface characteristics of hydraulic fractures were quantified based on three-dimensional topography scanning technology, combined with fractal dimension and fracture area calculation method, the results showed that with the increase of vertical stress difference coefficient, the fractal dimension and fracture area decreased. Since shale is stratified, and the transformation of reservoir is mainly reflected in the enhancement of fracture complexity through tensile failure, Xsite discrete grid method was used to study the influence of fracture propagation behavior with different bedding strengths. The results showed that when the bedding tensile strength was high, hydraulic fractures were easy to pass through the bedding, and when the bedding tensile strength was low, hydraulic fractures were easy to be captured by natural fractures. In addition, tensile cracks were easy to form when the tensile strength of bedding was low, shear cracks were easy to form when the strength of bedding was high, and the fracture volume was larger when the strength of bedding was low. This study provides a theoretical basis for hydraulic fracturing in engineering.

In this paper, based on smoothed-particle hydrodynamics-finite element method, numerical models of plunger squeezing water at a sinusoidal velocity were established to simulate self-excited pulse water jet (SEPWJ). RHT constitutive model was adopted to describe the damage and failure of coal rock impacted by water jet. The morphological evolutions of broken pits and timeliness of rock-breaking efficiency of SEPWJ and continuous water jet (CWJ) under the conditions with and without stress loadings were obtained and compared. The evolution laws of damage and stress inner coal rock induced by jet impact, and the failure mechanism were revealed. And the influences of different stress loading magnitudes on the fracture characteristics of coal rock were investigated. The results show that the morphologies of broken pits formed by self-excited pulse jet undergo changes in a semi-circular, U-shaped, V-shaped, and bullet shaped in sequence under the stress-free loading condition. When applying one-dimensional (1D) and 2D stress loadings, the shallow but wide broken pits with laminar main cracks along the stress loading direction and the inverted trapezoidal bowl broken pits are formed, respectively. With the increase of 1D stress, the depth and width of broken pits slightly decrease as a quadratic parabolic function and linearly increase, respectively. And the broken pit width and area both show an exponential slow decreasing trends with the increasing 2D stress. SEPWJ can induce higher stresses to cause the earlier occurrence of initial damage and the shorter duration of damage accumulation to coal rock than CWJ, which leads to a better rock-breaking effect. The surface and deeper coal rock elements are broken mainly due to compressive shear stresses. The 2D stress loading delays the initial damage occurrence and prolongs the damage accumulation duration due to inhibitory effect of stress loading on jet impact.

High-flux solar simulator (HFSS) commonly serves as a vital instrument for conducting material testing and thermochemical experiments, offering valuable applications in the fields of photovoltaic cells and concentrated solar energy. This paper proposes a continuously adjustable HFSS based on light-emitting diodes (LEDs), which can be employed for experimental testing in the solar cell aging. First, an irradiation unit module has been built using high-power LEDs and total internal reflection lenses, and the irradiation performance of the single unit has been validated. In theory, a dome layout model is proposed, in which a detailed geometric analysis is provided for the maximum number of units that can be accommodated on the dome, considering unit size and dome dimensions. Subsequently, aluminum disc has been used as thermal flux sensors, and the irradiation distribution of the system is characterized using a charge-coupled device observation camera and Lambertian board. The results indicate that the system offers an adjustable average flux ranging from 1.6 to 9.04 kW/m² when the system input current is in the range of 7.2–54 A. Additionally, the system demonstrates a spatial nonuniformity of 2% within a 10-mm diameter (Φ = 10 mm) region test region and temporal instability of 2% within 30 min.

The layout of methane sensors in the working face cannot meet the needs for monitoring methane concentrations within confined spaces, and it is challenging to determine the precise locations for manual inspections. Therefore, the working face is firstly divided into different areas and grids. Then combined with the characteristics of methane emissions and the measured data on site, the boundary conditions of simulation experiments are set up and the research is carried out on the diffusion law of methane in the confined space of the working face under different conditions. The experimental results show that methane emission intensity from coal walls affects its distribution. As emission intensity rises, methane nearer the coal wall decreases, while methane further away increases. Among coal mining points, point 2 shows the widest methane diffusion range. Rising wind speeds decrease methane diffusion from the coal wall, increasing vertical diffusion distance. Methane from the coal wall shifts to the air inlet, while methane from the mining point diffuses increasingly to the downwind side. The location of the maximum methane concentration generated from falling coal and its transportation process is only related to the location of the coal mining point. The key areas for methane monitoring in confined spaces of the working face should be the overlapping locations of the vertical-3 and vertical-4 areas and the horizontal-1 and horizontal-3 areas. The key areas for manual inspection should be the overlapping locations of the vertical-2 and vertical-3 areas and the horizontal-1 area.

Coal combustion is a major power source in the world, and energy conservation and environmental protection are now the top priorities in terms of carrying out the strategy for continuous and persistent development in power generation. The intricate coal combustion process must be investigated to present the process inside a live boiler as accurately as possible. In this study, the ANSYS FLUENT program is used to compare two species models namely, species transport (STM) and nonpremixed model (NPM). The two models are run with similar geometry and boundary conditions. It was found that the STM enables entering of the species reactions and activates a selection for the crucial coal combustion and devolatization processes. The NPM combustion process takes place with the assumption that combustion is in equilibrium, a Probability Density Function (PDF) mixture table is calculated first before the simulation can be run. Both submodels can depict the combustion process for a CFPP boiler providing temperature gradients within the boiler with species composition throughout the boiler. The NPM does not track species individually through the boiler, limiting model validation data. The STM was found to be suitable since it provided more comprehensive coal combustion results, that can be used for model validation.

To solve the problem of controlling large deformation of surrounding rock in deep soft rock roadway, the distribution characteristics and deformation mechanism of surrounding rock cracks in soft rock roadway under different lateral pressure coefficients are studied using numerical simulation, theoretical analysis, and field measurement. The results show that under different lateral pressure coefficients, the range of surrounding rock cracks shows three forms: round, oval, and butterfly. No matter what lateral pressure coefficient the roadway is in, the surrounding rock cracks always appear in the plastic zone, and there is a high correlation between the surrounding rock crack range and the plastic zone. The stress characteristics of the surrounding rock in the plastic zone include two main aspects. One is that the direction of the principal stress of the surrounding rock is deflected, which is manifested as an annular distribution of the direction of the maximum principal stress around the roadway. The direction of the minimum principal stress in the upper part of the roadway points to the center of the roadway, and the direction of the minimum principal stress in the lower part of the roadway deviates from the center of the roadway. Second, the ratio of the maximum to minimum principal stress in the surrounding rock is large. Under this stress characteristic, the surrounding rock in the plastic zone has strong shear dilation. The shear dilation makes the crack of the surrounding rock open so that the surrounding rock is squeezed into the roadway space, and then the roadway produces large deformation. Due to the large range of cracks in the butterfly-shaped plastic zone, the shear dilation deformation produced by the butterfly-shaped plastic zone is far more than that of the round/oval plastic zone. According to the crack range of roadway surrounding rock under different lateral pressure coefficients, the corresponding support scheme is put forward. Field experiments show that the support scheme can effectively control the deformation of surrounding rock and meet the requirements of roadway use.

Solid oxide fuel cells (SOFCs) are highly promising devices for efficient and low-emission energy conversion. The effective triple-phase boundary (TPB) density refers to the fraction of percolated TPB density that effectively contributes to the current production during cell operation. This is one of the most fundamental and least understood aspects of the cell design and performance assessment. This study methodically investigates the effective TPB density, using a computational fluid dynamics model based on the TPB-based kinetics and its correlation with the active anode thickness. Experimental data from previously published studies with varying thicknesses of anode functional layer and operating regimes are utilized to validate the model. The results of this study reaffirm that a significant fraction of the percolated TPB density in SOFCs remains unused during cell operation. This finding emphasizes the need to consider the effective TPB density for theoretical and experimental investigations focusing on optimizing cell performance. Furthermore, an inverse relationship is observed between the effective TPB density and the active anode thickness; a lower active anode thickness corresponds to a higher effective TPB density and vice versa. These findings contribute to advancing sustainable energy systems by guiding the development of more efficient SOFC designs and operational strategies that effectively utilize TPB sites.

The evolution characteristics of pores and fractures in coal after liquid carbon dioxide (CO₂) phase change are important factors that determine the permeability increase effect. Therefore, it is critical to correctly understand the influences of liquid CO₂ phase change on pores and fractures in coal. The changes of adsorption and desorption isotherm, pore size, pore volume, and specific surface area of fractured coal and fractured coal were compared by low temperature liquid nitrogen adsorption experiment. In addition, a scanning electron microscope was adopted to observe fracture characteristics of fractured and unfractured coal samples and analyze changes in the connectivity and fracture development. Experimental results show that the fractured coal samples exhibit better hysteresis loops and a larger proportion of gas desorption than the unfractured ones. Fractured coal samples contain more developed pores and fractures compared with unfractured ones, and their fragmentation degree, pore diameter, fracture width, and connectivity of pores and fractures are also better. Besides, the closer the samples from the fracturing boreholes are, the better the fracturing effect. This indicates that liquid CO₂ phase change can effectively enhance the gas transport capacity in pores and fractures in coal. The research results provide a solid basis for the better application of liquid CO₂ phase-change fracturing to the prevention of coal and gas outburst disasters and the realization of efficient gas extraction in deep coal seams.

Taking a rear-wheel drive pure electric vehicle as the research object, considering the safety during braking and improving energy recovery rate, a study was conducted on the distribution strategy of front and rear axle braking force. During the braking process, the feedback braking force of the motor and the hydraulic braking force with an electronic stability controller (ESC) were coordinated and controlled, to ensure that the total required braking force was met. A fuzzy logic controller has been designed, with three variables of battery state of charge, vehicle speed, and braking intensity as inputs, and a modified motor braking ratio as output variable to prevent wheel lockup. Using Cruise software, a co-simulation model was established with Amesim and Simulink, and simulation validation was conducted on the braking process and cycling conditions. The simulation results showed that the brake recovery strategy based on fuzzy control can effectively improve the vehicle's control performance and energy recovery rate compared to the Economic Commission of Europe regulation. The NEDC (New European Driving Cycle) working condition improved by 10.41% and the CLTC-P (China Light-duty Vehicle Test Cycle-passenger) working condition improved by 10.57%. Effectively improving power consumption per 100 km, NEDC decreased by 1.81% and CLTC-P decreased by 2.62%.