To investigate the influence of the guide vane height on the cyclonic flow characteristics of guide vane cyclones, this paper mainly adopts a combination of numerical simulation and physical ...experiments, taking the guide vane height as the research object, analysing the internal spiral flow generation law through the flow velocity distribution in each section of the cyclone and the change trend along the course and comparing the tangential velocity, radial velocity and axial velocity characteristics of the cyclone at different guide vane heights. The results show that the tangential velocity increases with the increase in the guide vane height on the cyclone and then decreases. When the ratio between the height of the guide vane and the inner radius of the cyclone is in the range of 0.5–0.7, a higher−strength and more stable spiral flow can be produced, and the tangential velocity reaches the maximum when the guide vane height is 30 mm and the height−to−diameter ratio is around 0.6. As the height of the guide vane increases, the radial velocity area towards the wall of the tube increases, while the radial velocity area towards the tube axis decreases. The overall distribution of axial flow velocity is similar to that of turbulent flow in a circular tube, and the velocity increases with increasing height of the guide vane. The conclusion of this paper provides a theoretical basis for further optimisation of the cyclone structure parameters.
The fluid stress or flow-induced vibration of annular gap flow always has some influence on the stable working conditions of a hydraulic machine. A time-averaged analysis of flow may not have to ...explicitly acknowledge these factors. Accordingly, a finite-axial-length annular gap was measured via particle image velocimetry (PIV), with inner boundary motion and a stable outer boundary. As a statistic result regarding the fluid stress, the Reynolds stresses soared in the first region, were sustained in the middle region, but decreased at last. The flow had a higher convective transportation intensity in the radial direction than in other directions. Flow diagnostics were also performed by proper orthogonal decomposition (POD). As a result, the coherent structures were found. Then, the power spectrum density (PSD) functions were also calculated for finding the flow-induced vibration characteristics; the functions had high amplitude in the low-frequency domain and low amplitude in the high-frequency domain, with an order of magnitude between the two amplitudes of 10−1 to 10−2. In addition, the frequency was higher at a smaller gap width in the middle-frequency domain, but the condition was the opposite in the high-frequency domain. In conclusion, the fluid stresses were changeable and uneven along the flow direction, and flow-induced vibration obviously existed. Remarkably, the turbulence characteristics of the annular gap flow were not “laminar approximating,” while the diameter ratio of the gap was 0.6 to 0.8.
The seepage properties of natural gravel are one of the problems to be considered in seepage project designs. In this paper, the seepage properties of the natural gravel with particle sizes of 5, 20 ...and 60 mm were investigated under different laying conditions. The effect of the particle size, laying depth, bulk density and pressurized head on the seepage properties of the natural gravel was analyzed by using the combined methods of theoretical analysis with physical model test. The results showed that the seepage flow in the natural gravel was non-laminar flow in the test conditions described in this paper. Meanwhile, the relationship between particle size, laying depth, bulk density, pressurized heads and seepage property was established. The seepage discharge increased with the increase of the pressurized head and particle size, and decreased with the increasing of laying depth and bulk density. The critical laying depth and bulk density can be obtained when the seepage discharge becomes zero. The empirical formula of the seepage discharge of natural gravel with different particle sizes, laying depths, bulk densities and pressurized heads was obtained with the method of nonlinear regression, which can be expressed as:
Q
=
5
.
9546
d
0
.
3713
γ
−
0
.
2974
L
−
0
.
1156
H
0
.
1307
−
5
.
6614
. The empirical formula was experimentally validated. The maximum relative error did not exceed 6.73%, proving that the empirical formula of the seepage discharge of natural gravel was rational. The results can provide an important reference to further studying the seepage properties of macropore media, and form a theoretical basis for applying the natural gravel in the seepage projects.
Hydrocyclone with guide vanes is one type of swirl flow launching device without energy input. For researching the flow characteristics of that hydrocyclone, the flow distribution of the sections and ...their variation along the flow were studied using numerical simulation and physical experiment. In addition, the flow field was convenient to be divided into three-dimensional velocities: axial velocity, circumferential velocity, radial velocity and the static pressure. The result showed that the water flow had obvious diversion by the effect of guide vanes. The axial velocity varied into the distribution of higher values emerging away from the pipe wall and the surfaces of guide vanes, and the value was higher on downstream surfaces than upstream surfaces of the guide vanes. The radial velocity’s direction pointed at the axis of pipe on upstream surfaces, and pointed at the pipe wall on the downstream surfaces of the guide vanes; the influenced range was larger in sections along the flow. The circumferential velocity increased along the flow, closing the distorted guide vanes; the value of that velocity was larger closer to the guide vanes, especially the downstream surfaces of the guide vanes. The static pressure decreased along the flow, and the value was larger on the upstream surfaces than the downstream surfaces of the guide vanes. The results can provide some theory references to improve the construction of the hydrocyclone.
Converting ubiquitous environmental energy into electric power holds tremendous social and financial interests. Traditional energy harvesters and converters are limited by the specific materials and ...complex configuration of devices. Herein, it is presented that electric power can be directly produced from pristine graphene oxide (GO) without any pretreatment or additives once encountering the water vapor, which will generate an open‐circuit‐voltage of up to 0.4–0.7 V and a short‐circuit‐current‐density of 2–25 µA cm−2 on a single piece of GO film. This phenomenon results from the directional movement of charged hydrogen ions through the GO film. The present work demonstrates and provides an extremely simple method for electric energy generation, which offers more applications of graphene‐based materials in green energy converting field.
Electric power can be directly produced from pristine graphene oxide (GO) without any pretreatment or additives under water vapor. A single GO film will generate an open‐circuit‐voltage of up to 0.7 V and a short‐circuit‐current‐density of 25 µA cm−2. This work demonstrates and provides an extremely simple method for electric generation, promising for applications in green energy converting field.
•Different methods were used to extract Dendrobium officinale polysaccharide (DOP).•Freeze-thawing cold-pressing had higher extraction yield and molecular weight for DOP.•DOP from Freeze-thawing ...cold-pressing method had stronger antioxidant activities.•Freeze-thawing cold-pressing should be considered as the best method for DOP.
The purpose of this study was to screen the optimum extraction of polysaccharides (DOP) from Dendrobium officinale stem. Firstly, different methods, including hot water extraction (HWE), cold-pressing (CP), freeze-thawing cold-pressing (FTCP), ultrasonic-assisted hot water extraction (UHWE), microwave-assisted hot water extraction (MHWE) and enzyme-assisted hot water extraction (EHWE), were employed to extract DOP under their respective best parameters. Then, the extraction yield, structure and antioxidant activity of the polysaccharides from different extraction methods were compared under the same condition. The data implied that UHWE and FTCP possessed higher extraction yield than the other extraction methods. Besides, DOPCP and DOPFTCP had higher molecular weight than the other polysaccharide samples. More importantly, DOPFTCP had the highest antioxidant activity. Overall, DOPFTCP exhibit high extraction yield, well-preserved molecular chains and best antioxidant activity, all these indicated FTCP was the most suitable method to extract DOP.
Display omitted
•Novel NMCZ-x heterostructure photocatalysts are synthesized for the first time.•The development of preferred orientation in CZ-0.1 by adjusting the 2D Ni-MOFs content.•Synergy ...between Cu doping and catalytic platform makes better PHE activity.•Efficient H2 evolution and excellent stability are realized over NMCZ-10 composite.•The photocatalytic mechanism of 2D MOFs and Pt as double co-catalysts is revealed.
Doping strategy has been widely studied and applied to design visible light driven photocatalysts, which can introduce defect level and modulate the band structure of photocatalysts to improve the photocatalytic activity. In addition, it is of great significance to introduce a catalytic platform in the photocatalytic H2 evolution (PHE) system, which can also greatly improve the photogenerated carriers transport capacity. As is known to all, 2D materials have been proven to be crucial platform for PHE reactions. In view of this, we have successfully prepared the 2D Ni-MOFs/Cu-doped Zn0.5Cd0.5S-x (abbreviated as NMCZ-x) heterojunction with the preferential orientation of crystals, which endows the catalyst with extremely excellent PHE activity and chemical stability. DFT calculations indicated that Cu atoms served as the center of electron capture after substituting Zn atoms, and Cu doping will introduce defect level. The NMCZ-10 complex achieves the best PHE activity and superior structural stability. This work highlights the importance of the synergistic effect between element doping and catalytic platform for the preparation of advanced photocatalysts.
Biodegradable microplastics (BMPs) pose serious environmental problems to soil organisms, and their adsorption capacity might make pesticides more dangerous for soil organisms. Therefore, in this ...study, polylactic acid (PLA) BMPs and imidacloprid (IMI) were used as a representative of BMPs and pesticides, respectively. Eisenia fetida was used as a test animal to investigate the effects of environmentally relevant concentrations of single and compound contaminated PLA BMPs and IMI on mortality, growth, number of offspring, tissue damage, and gut microorganisms of E.fetida. Exposure to PLA BMPs treatment and PLA BMPs + IMI treatment resulted in a sustained increase in E.fetida mortality, reaching 16.7% and 26.7%, respectively. The growth inhibition rate of single treatments was significantly increased. The compound contamination had the greatest effect on E.fetida offspring compared to the control. PLA BMPs and IMI cause histological damage to E.fetida, with the compound treatment causing the most severe damage. Based on the results of 16S sequencing, the bacterial communities in E.fetida gut and soil treated to PLA BMPs and IMI were significantly different. PLA BMPs + IMI treatment suppresses the abundance and diversity of E.fetida gut microorganisms, disrupting the homeostasis of bacterial communities and causing immune and metabolic dysfunction. These findings highlight the more severe damage of combined PLA BMPs and IMI pollution to E.fetida, and help to assess the risk of earthworm exposure to environmentally relevant concentrations of PLA BMPs and IMI.
Display omitted
•PLA BMPs and IMI cause histological damage in Eisenia fetida.•Combined contamination affects the mortality and reproduction rate.•The earthworm gut microbiota was significantly different from the surrounding soil.•Combined pollution resulted in significant changes in the gut microbiota.
As an important part of low-carbon ecological city construction, green building is also an objective requirement of sustainable development. Based on the green building panel data of 30 provincial ...administrative regions in China from 2010 to 2020, the super-efficiency SBM model combined with the three-stage DEA model was adopted to obtain the green building efficiency value that was closer to the real situation by excluding the influence of environmental factors and statistical noise. Green buildings in China have only been developing for just over ten years and are still in the initial stage of spatial aggregation in which transportation infrastructure plays an important role in scale effect. This manuscript focuses on analyzing the influence factors, intensity and direction of transportation infrastructure on green building efficiency. The results show that: (1) The agglomeration effect is obvious in the area of green buildings with high efficiency, but the radiation effect is not strong in low-efficiency area. (2) Municipal transportation infrastructure investment, road surface area, per capita number of stations and interregional traffic network density have a positive impact on green building efficiency, while freight volume has a negative impact.
The oxidation of tetravalent uranium significantly affects its use as a reducing agent. This study focuses on a tetravalent uranium solution prepared through the hydrogen reduction process in the ...nitric acid system, excluding factors such as hydrazine that could impact the oxidation of tetravalent uranium. The study thoroughly investigates the influencing factors of tetravalent uranium oxidation, including temperature, acidity, etc. It is found that temperature has a critical point of impact on the oxidation of tetravalent uranium at 60 °C. Below 60 °C, although the oxidation rate of tetravalent uranium increases with temperature, there is no significant leap in rapid oxidation. However, at 60 °C, tetravalent uranium undergoes rapid oxidation after an induction period. Through chemical composition analysis and experimental observation, the study clarifies the oxidation reaction mechanism and uncovers the reasons behind the induction period, providing guidance for the use of tetravalent uranium as a reducing agent.
PDF
