Search Results (16)

Here, a pure and systematic numerical study is conducted to investigate the detonation propagation in a curvature bend by focusing on the combined effect of curvature and cross-section area with a simple two-step chemical reaction model. In a channel with a small radius of curvature R/λ < 10, the detonation wave presents a periodical failure-reinitiation mode. The detonation wave near the inner wall cannot sustain itself due to the strong curvature effect. In contrast, the compression of the outer wall strengthens the front and can form a transverse detonation wave to re-initiate the failed detonation near the inner wall. In a channel with a large radius of curvature R/λ > 10, the inner wall’s weak rarefaction effect is not strong enough to completely quench the detonation wave. In the same way, the numerical results also show that a large area expansion rate inevitably produces a strong rarefaction effect near the inner wall, causing wave front decoupling and even failure. According to the radius of the curvature and the area increase rate, there are three different modes of detonation propagation: stable, critical, and unstable. By defining a new parameter κ to characterize different detonation modes and by considering both the curvature and area expansion effect, we found that the threshold κ = 0.33 can be used to distinguish the unstable and critical modes. Full article

Exploration practice has proved that preservation conditions are one of the critical factors contributing to shale gas enrichment in the Middle Yangtze area. Well Yidi2 is the discovery well of Cambrian shale gas in this area. The paleo-fluid evolution and its implication for preservation conditions of shale gas remains unclear, posing challenges for shale gas exploration and development. In this study, through systematic analysis of fluid inclusions in fractrue-filling vein of the entire core section of this well, combined with carbon and oxygen isotope tests of veins and host rocks, a paleo-fluid profile was established to explore the formation environment of Cambrian paleo-fluids and their implications for the preservation conditions of the Shuijingtuo Formation (SJT Fm.) shale gas. The results suggest that fractures in the SJT Fm. shale at the base of Cambrian Series 2 mainly formed during the deep burial hydrocarbon generation stage, trapping a large number of liquid hydrocarbon inclusions. Subsequently, numerous high-density methane inclusions and a few of gas-liquid two-phase inclusions were trapped. The SO₄²⁻, Ca²⁺ and Mg²⁺ content of fluid inclusion groups in the veins decreased from the Qinjiamiao Formation (QJM Fm.) at the bottom of Cambrian Series 3 upward and downward respectively, and the rNa⁺/rCl⁻ ratio was the lowest in the SJT Fm. and increased overall upward. The δ¹³C values of calcite veins in Tianheban Formation (THB Fm.)-Shipai Formation (SP Fm.) of the middle Cambrian Series 2 and the Loushanguan Formation (LSG Fm.) of the Cambrian Series 3 were lighter compared to the host rocks. Results indicate the later tectonic activities in this area were relatively weak, and the shale interval remained in a state of high gas saturation for a long time. The QJM Fm. was the main source of high-salinity brine, and the SJT Fm. had strong self-sealing properties and was relatively less affected by external fluids. However, the pressure evolution of high-density methane inclusions in the SJT Fm. indicated that the pressure coefficient of the shale section significantly decreased during the Indosinian uplift and erosion stage. The veins in the THB-SP and LSG Fms. were closely related to the oxidation of hydrocarbon gases by TSR (thermochemical sulfate reduction) and the infiltration of atmospheric water, respectively. Therefore, the paleo-fluid in the fractures of Well Yidi2 have integrally recorded the whole geological process including the evolution from oil to gas, the backflow of high-salinity formation water, the upward escape of shale gas, and the process of shale gas reservoirs evolving from overpressure to normal pressure. Considering that Well Yidi2 area is located in a relatively stable tectonic setting, widely distributed fracture veins probably enhance the self-sealing ability, inhibiting the rapid escape of SJT Fm. shale gas. And the rapid deposition of Cretaceous also delayed the loss of shale gas to some extent. The combination of these two factors creates favorable preservation conditions of shale gas, establishing the SJT Fm. as the primary exploration target in this area. Full article

A submersible sewage pump is designed for conveying solid–liquid two-phase media containing sewage, waste, and fiber components, through its small and compact design and its excellent anti-winding and anti-clogging capabilities. In this paper, the computational fluid dynamics–discrete element method (CFD-DEM) coupling model is used to study the influence of different conveying conditions and particle parameters on the wear of the flow components in a submersible sewage pump. At the same time, the energy balance equation is used to explore the influence mechanism of different tip clearance sizes on the internal flow pattern, wear, and energy conversion mechanism of the pump. This study demonstrates that increasing the particle volume fraction decreases the inlet particle velocity and intensifies wear in critical areas. When enlarging the tip clearance thickness from 0.4 mm to 1.0 mm, the leakage vortex formation at the inlet is enhanced, leading to increased wear rates in terms of the blade and volute. Consequently, the total energy loss and turbulent kinetic energy generation increased by 3.57% and 2.25%, respectively, while the local loss coefficient in regard to the impeller channel cross-section increased significantly. The findings in this study offer essential knowledge for enhancing the performance and ensuring the stable operation of pumps under solid–liquid two-phase flow conditions. Full article

The establishment of protective forests plays a crucial role in mitigating soil erosion on slopes within hilly and gully regions. However, in practical applications, the configuration of protective forests on slopes is intricate and diverse, and the suitability and rationality of different configuration patterns for various slope sections have not been thoroughly investigated. This study focuses on a 40-year-old artificial protective forest, examining 16 different configuration patterns on the top, middle, and lower slopes. It compares the growth conditions, community structure stability, and characteristics of the saturated soil’s hydraulic conductivity. The findings indicate that the top slope should be identified as a critical area for slope protection. The optimal configuration for this area is the “tree + grass” pattern with a spacing of 5 m × 5 m, which promotes the optimal growth of tree species and effectively reduces the surface runoff of gravel particles ranging from 1 cm to 3 cm in diameter. On the middle slope, the “tree + shrub + grass” structure proves effective in slowing down the erosive force of slope runoff. The recommended spacing for trees is 5 m × 6 m, and for understory shrubs, it is 1 m × 6 m. This configuration pattern results in the most stable structure for the plant community and maximizes the water conservation potential of forest litter. By analyzing the characteristics of the saturated soil’s hydraulic conductivity, we find that the complexity of the plant configuration on the lower slopes is correlated with a greater coefficient of variation in the saturated soil’s hydraulic conductivity. Nevertheless, there is no significant difference in the average soil saturated hydraulic conductivity per unit area between the different configuration patterns. Consequently, the lower slope can rely on the natural recovery of herbaceous plants. The results of this research contribute valuable scientific and technical insights to the management of soil erosion in hilly and gully areas, both in China and around the world. Full article

X-ray detection has widespread applications in medical diagnosis, non-destructive industrial radiography and safety inspection, and especially, medical diagnosis realized by medical X-ray detectors is presenting an increasing demand. Perovskite materials are excellent candidates for high-energy radiation detection based on their promising material properties such as excellent carrier transport capability and high effective atomic number. In this review paper, we introduce X-ray detectors using all kinds of halide perovskite materials along with various crystal structures and discuss their device performance in detail. Single-crystal perovskite was first fabricated as an active material for X-ray detectors, having excellent performance under X-ray illumination due to its superior photoelectric properties of X-ray attenuation with μm thickness. The X-ray detector based on inorganic perovskite shows good environmental stability and high X-ray sensitivity. Owing to anisotropic carrier transport capability, two-dimensional layered perovskites with a preferred orientation parallel to the substrate can effectively suppress the dark current of the device despite poor light response to X-rays, resulting in lower sensitivity for the device. Double perovskite applied for X-ray detectors shows better attenuation of X-rays due to the introduction of high-atomic-numbered elements. Additionally, its stable crystal structure can effectively lower the dark current of X-ray detectors. Environmentally friendly lead-free perovskite exhibits potential application in X-ray detectors by virtue of its high attenuation of X-rays. In the last section, we specifically introduce the up-scaling process technology for fabricating large-area and thick perovskite films for X-ray detectors, which is critical for the commercialization and mass production of perovskite-based X-ray detectors. Full article

The Changbei gas field is dominated by wells with large horizontal displacement, which have exhibited high gas production performance at an early stage of development. With the decrease in reservoir pressure, the liquid loading in the gas well is relatively high and gas production rapidly decreases. Therefore, suitable drainage measures are required to maintain stable gas production. Based on the characteristics of the unconnected oil jacket of gas wells in Changbei, a velocity string was used for drainage. A critical liquid-carrying model was established to determine the location of liquid loading in horizontal gas wells in Changbei. First, the coefficients of the liquid-carrying model were determined through theoretical analysis of the characteristics of the gas well formation. Then, the depth setting of the velocity string was analyzed. The critical liquid-carrying model was employed to calculate the liquid-carrying flow rate of each section; the calculated flow rates were compared with the actual flow rates to determine whether fluid accumulation occurred in each section of the gas well. Thereafter, with the help of the oil and casing position, the suitable setting position of the velocity string was determined. The formation fluid was driven from the tubing into the casing owing to the increase in the overflow area, based on the principle of reducer fluid mechanics. The fluid velocity in the larger overflow cross-section decreased, thereby reducing the drainage capacity of the gas well and resulting in liquid loading. Finally, a timing analysis was performed. After the formation pressure decreased, the well production and flow rate changes were analyzed by placing two velocity strings of different sizes at different wellhead pressures in the gas well with fluid accumulation. The results indicated that although the velocity string was set at a position suitable for fluid drainage, fluid accumulation still occurred after a production period, thus necessitating replacement deliquification. Full article

The relatively stable MOFs Alfum, MIL-160, DUT-4, DUT-5, MIL-53-TDC, MIL-53, UiO-66, UiO-66-NH₂, UiO-66(F)₄, UiO-67, DUT-67, NH₂-MIL-125, MIL-125, MIL-101(Cr), ZIF-8, ZIF-11 and ZIF-7 were studied for their C₆ sorption properties. An understanding of the uptake of the larger C₆ molecules cannot simply be achieved with surface area and pore volume (from N₂ sorption) but involves the complex micropore structure of the MOF. The maximum adsorption capacity at p p₀⁻¹ = 0.9 was shown by DUT-4 for benzene, MIL-101(Cr) for cyclohexane and DUT-5 for n-hexane. In the low-pressure range from p p₀⁻¹ = 0.1 down to 0.05 the highest benzene uptake is given by DUT-5, DUT-67/UiO-67 and MIL-101(Cr), for cyclohexane and n-hexane by DUT-5, UiO-67 and MIL-101(Cr). The highest uptake capacity at p p₀⁻¹ = 0.02 was seen with MIL-53 for benzene, MIL-125 for cyclohexane and DUT-5 for n-hexane. DUT-5 and MIL-101(Cr) are the MOFs with the widest pore window openings/cross sections but the low-pressure uptake seems to be controlled by a complex combination of ligand and pore-size effect. IAST selectivities between the three binary mixtures show a finely tuned and difficult to predict interplay of pore window size with (critical) adsorptive size and possibly a role of electrostatics through functional groups such as NH₂. Full article

Oil pipeline construction and operation in mountainous areas have increased in southwestern China, with oil consumption increasing. Such liquid pipelines laid in mountainous areas continuously undulate along the terrain, resulting in many large elevation difference pipe segments. Serious gas block problems often occur during the commissioning process of these pipelines due to the gas/air accumulation at the high point of the pipe, which causes pipeline overpressure and vibration, and even safety accidents such as bursting pipes. To solve this problem, the gas–liquid replacement model and its numerical solution are established with consideration of the initial gas accumulation formation and the gas segment compression processes in a U-shaped pipe during the initial start-up operation. Additionally, considering the interactions of the gas-phase transfer in the continuous U-shaped pipe, and the influence of the length, inclination angle, and backpressure on the air vent process, the gas migration model for a continuous U-shaped pipe is established to predict the gas movement process. Finally, the field oil pipe production data were applied to verify the model. The results demonstrate that the maximum deviation between the calculated pressure during the start-up process and real data is 0.3 MPa, and the critical point of crushing the gas in the pipe section is about 0.2 Mpa. Additionally, the results show that the mass transfer of the gas section in the multi-pipe hydraulic air vent process causes the gas accumulation section to increase in downstream of the pipe. This study’s achievements can provide theoretical guidance and technical support for the safe and stable operation of continuous undulating liquid pipelines with large drops. Full article

Developing energy from renewable sources and modernizing the energy system are critical components of China’s efforts to combat climate change. Policymakers and authorities have made significant attempts to bring them. However, one of the major impediments to China’s energy revolution is financial limitations, which are inextricably linked to the country’s economic growth. The present research paper intends to investigate the relationship between economic growth and sustainable financial development on the use of energy from renewable sources in both the short and long run in the context of China. To achieve this, the researchers have utilized the panel data consisting of 10 years from 2011 to 2020. When compared to cross-sectional and time-series data samples, the panel data model offers many benefits. For starters, the panel data includes information on the passage of time and the cross-sectional area. Another benefit of using panel-data models with a larger degree of freedom is that they provide more stable and reliable estimates across short periods across cross-sections. In the case of the short run, there is a positive relationship between economic and financial development and the use of energy from renewable sources in the context of all of China. While in the case of long-term effects, the results indicate the adverse impact of financial development on the use of energy from renewable sources in the western regions of China. These results were deduced using the causality test Granger proposed to determine the path of the causal relationship and the direction of the relationship between the variables. These results indicated that the relationship between economic and financial development in east China was unidirectional, and the nature of the underlying relationship was causal. Meanwhile, in east and west China, economic development in China as a whole has been unidirectionally increasing energy from renewable sources. Our empirical findings suggest many strategies for promoting the growth of energy from renewable sources. Full article

Mangrove forests have declined worldwide and understanding the key drivers of regeneration at different perturbation levels can help manage and preserve these critical ecosystems. For example, the Ramsar site # 1602, located at the Tampamachoco lagoon, Veracruz, México, consists of a dense forest of medium-sized trees composed of three mangrove species. Due to several human activities, including the construction of a power plant around the 1990s, an area of approximately 2.3 km² has suffered differential levels of perturbation: complete mortality, partial tree loss (divided into two sections: main and isolated patch), and apparently undisturbed sites. The number and size of trees, from seedlings to adults, were measured using transects and quadrats. With a matrix of the abundance of trees by size categories and species, an ordination (nMDS) showed three distinct groups corresponding to the degree of perturbation. Projection matrices based on the size structure of Avicennia germinans showed transition probabilities that varied according to perturbation levels. Lambda showed growing populations except on the zone that showed partial tree loss; a relatively high abundance of seedlings is not enough to ensure stable mangrove dynamics or start regeneration; and the survival of young trees and adult trees showed high sensitivity. Full article

Turbine guide vanes are among the most critical and complex turbine parts. As an entire engine comprises a significant number of vanes, simplification of the measurement process translates into overall time and money savings. The key to simplification is to define critical areas for inspection, which enables relaxation of strict inspection standards in all areas of stable process manufacturing. The method described herein can help engineers to achieve savings in inspection time and cost, at the same time ensuring the correct shape of vanes as the approach used in this work places great emphasis on correlations between measurements, working conditions, and manufacturing abilities. Another element of the novelty of this approach is an atypical hybrid convention for the crossing of vertical and horizontal inspection paths, assuring a correlation between the measured sections. Although this novel approach was used to measure the geometry of a cast turbine guide vane, it can be easily implemented to measure the geometry of any other element of complex shape. Full article

The critical stable sectional area (CSSA) for surge tanks corresponds to the critical stable state of hydropower stations and is an important index to evaluate the stability of the turbine regulation system. The research on CSSA for surge tanks is always one of the most important topics in the area of transient processes of hydropower stations. The CSSA for surge tanks provides the value basis for the sectional area of surge tanks. In engineering practice, the CSSA for surge tanks is widely used to guide their hydraulic design. This paper provides a systematic literature review about the CSSA for surge tank of hydropower stations. Firstly, the CSSA for surge tanks based on hydraulic transients is discussed. Secondly, the CSSA for surge tanks based on hydraulic-mechanical-electrical coupling transients is presented. Thirdly, the CSSA for air cushion surge tanks is illustrated. Finally, the CSSA for combined surge tanks, i.e., upstream and downstream double surge tanks and upstream series double surge tanks, is presented. In future research, the CSSA for surge tanks of pumped storage power stations should be explored. The CSSA for surge tanks considering multi-energy complement is worth studying. Full article

Food chain length (FCL) is a critical measure of food web complexity that influences the community structure and ecosystem function. The FCL of large subtropical rivers affected by dams and the decisive factors are far beyond clear. In this study, we used stable isotope technology to estimate the FCL of fish in different reaches of the main stream in the Yangtze River and explored the key factors that determined the FCL. The results showed that FCL varied widely among the studied areas with a mean of 4.09 (ranging from 3.69 to 4.31). The variation of FCL among river sections in the upstream of the dam was greater than that in the downstream. Regression analysis and model selection results revealed that the FCL had a significant positive correlation with ecosystem size as well as resource availability, and FCL variation was largely explained by ecosystem size, which represented 72% of the model weight. In summary, our results suggested that ecosystem size plays a key role in determining the FCL in large subtropical rivers and large ecosystems tend to have a longer food chain. Additionally, the construction of the Three Gorges Dam has been speculated to increase the FCL in the impoundment river sections. Full article

Liquid–solid circulating fluidised beds (CFB) possess many qualities which makes them useful for industrial operations where particle–liquid contact is vital, e.g., improved heat transfer performance, and consequent uniform temperature, limited back mixing, exceptional solid–liquid contact. Despite this, circulating fluidised beds have seen no application in the micro-technology context. Liquid–solid micro circulating fluidised bed (µCFBs), which basically involves micro-particles fluidisation in fluidised beds within the bed of cross-section or inner diameter at the millimetre scale, could find potential applications in the area of micro-process and microfluidics technology. From an engineering standpoint, it is vital to know the solid circulating velocity, since that dictates the bed capability and operability as processing equipment. Albeit there are several studies on solid circulating velocity measurement in CFBs, this article is introducing the first experimental study on solid circulating velocity measurement in a CFB at micro-scale. The experimental studies were done in a novel micro-CFB which was fabricated by micro milling machining 1 mm² cross-section channels in Perspex and in a 4 mm² cross-section micro-CFB made by additive manufacturing technology. Soda-lime glass and polymethyl methacrylate (PMMA) micro-particles were employed as solid materials and tap water as the liquid medium. The digital particle image velocimetry (PIV) method was used as a measurement technique to determine the particle velocity in the micro-CFB system and validated by the valve accumulation technique using a novel magnetic micro-valve. The measured critical transition velocity, U_cr, is comparable to the particle terminal velocity, i.e., the normalised transition velocity is approximately 1 in line with macroscopic systems results and our previous study using simple visual observation. As in macroscopic CFB systems, U_cr decreased with solid inventory (1–9%) and finally becomes stable when the solid inventory is high enough (10–25%) and it increases with a reduction in particle size and density. Full article

Mariners navigating within Canadian waters rely on Canadian Hydrographic Service (CHS) navigational charts to safely reach their destinations. To fulfil this need, CHS charts must accurately reflect the current state of Canadian coastal regions. While many coastal regions are stable, others are dynamic and require frequent updates. In order to ensure that important and potentially dangerous changes are reflected in CHS products, the organization, in partnership with the Canadian Space Agency, is exploring coastal change detection through satellite remote sensing (SRS). In this work, CHS examined a hybrid shoreline extraction approach which uses both Synthetic Aperture Radar (SAR) and optical data. The approach was applied for a section of the Mackenzie River, one of Canada’s most dynamic river systems. The approach used RADARSAT-2 imagery as its primary information source, due to its high positioning accuracy (5 m horizontal accuracy) and ability to allow for low and high water line charting. Landsat represented the primary optical data source due to its long historical record of Earth observation data. Additional sensors, such as Sentinel-2 and WorldView, were also used where a higher resolution was required. The shoreline extraction process is based on an image segmentation approach that uses both the radar and optical data. Critical information was collected using the automated approach to support chart updates, resulting in reductions to the financial, human and time factors present within the ship-based hydrographic survey techniques traditionally used for chart improvements. The results demonstrate the potential benefit of wide area SRS change detection within dynamic waterways for navigational chart improvements. The work also demonstrates that the approach developed for RADARSAT-2 could be implemented with data from the forthcoming RADARSAT Constellation Mission (RCM), which is critical to ensure project continuity. Full article