Influence of Cavitation on Unsteady Vortical Flows in a Side Channel Pump

Previous investigation on side channel pump mainly concentrates on parameter optimization and internal unsteady vortical flows.However,cavitation is prone to occur in a side channel pump,which is a challenging issue in promoting performance.In the present study,the cavitating flow is investigated numerically by the turbulence model of SAS combined with the Zwart cavitation model.The vapors inside the side channel pump firstly occur in the impeller passage near the inlet and then spread gradually to the downstream passages with the decrease of NPSHa.Moreover,a strong adverse pressure gradient is presented at the end of the cavity closure region,which leads to cavity shedding from the wall.The small scaled vortices in each passage reduce significantly and gather into larger vortices due to the cavitation.Comparing the three terms of vorticity transport equation with the vapor volume fraction and vorticity distributions,it is found that the stretching term is dominant and responsible for the vorticity production and evolution in cavitating flows.In addition,the magnitudes of the stretching term decrease once the cavitation occurs,while the values of dilatation are high in the cavity region and increase with the decreasing NPSHa.Even though the magnitude of the baroclinic torque term is smaller than vortex stretching and dilatation terms,it is important for the vorticity production along the cavity surface and near the cavity closure region.The pressure fluctuations in the impeller and side channel tend to be stronger due to the cavitation.The primary frequency of monitor points in the impeller is 24.94 Hz and in the side channel is 598.05 Hz.They are quite corresponding to the shaft frequency of 25 Hz(fshaft=1/n=25 Hz)and the blade frequency of 600 Hz(fblade=Z/n=600 Hz)respectively.This study complements the investigation on cavitation in the side channel pump,which could provide the theoretical foundation for further optimization of performance.

Synergistic Modification of PVC with Nitrogen-Containing Heterocycle and Tung-Oil Based Derivative for Enhanced Heat Stabilization and Plasticization Behavior

The additives present in polyvinyl chloride(PVC)materials are the major source of organic by-products during PVC degradation.The thermal stabilizer and plasticizer are the main additives that endow PVC with the required properties during its processing.However,these two additives easily migrate when samples are obtained by physical mixing of the additives with PVC.This causes the reduction of PVC sample efficacy and the increase in the formation of organic by-products in the radiolysis process.In this work,two kinds of grafted PVC samples(tungoil derivative grafted PVC and Atz grafted PVC,abbreviated as P-GT4 and P-AZ3)were synthesized by chemical grafting of 3-amino-1,2,4-triazole(Atz)and tung-oil derivative on PVC,respectively.These two PVC samples were then blended at different mass ratios to obtain hybrid PVC materials with excellent plasticization,thermal stability and migration resistance ability.Differential scanning calorimetry(DSC),discoloration,Congo red test and thermogravimetric analysis(TGA)showed that when the mass ratio of P-GT4 to P-AZ3 in the mixed PVC resin was 1:3,the resulting P1:3-GT4-AZ3(P4)presented the best plasticization and thermal stability.The kinetics of thermal decomposition showed that the activation energy of P4 was much higher than that of the reference material[PVC/DOTP/CaSt2/ZnSt2,PVC/CZ41 for short]at mass lossα=20%and 80%.In addition,the leaching test showed that P4 material possessed excellent migration resistance ability.

具有超快电子传输能力的金/薄层氮化碳等离子光催化剂用于光催化产氢（英文）

光催化产氢可以直接将太阳能转化为化学能,是非常有前景的产氢技术之一.然而,光催化产氢的瓶颈在于如何提高光催化产氢效率和光催化剂的稳定性,以及降低产氢成本.因此,开发廉价、易于制备的产氢光催化剂引起人们广泛关注.作为一种非金属半导体光催化剂,石墨相氮化碳(g-C_3N_4)具有良好的物理化学性质,如良好的化学和热稳定性、极佳的光电性能、强的抗氧化能力等.更为重要的是,g-C_3N_4具有合适的能带结构,能够利用可见光.因此,g-C_3N_4已广泛应用于光催化降解、空气净化、光解水和光催化CO2还原等领域.然而,体相g-C_3N_4仍然暴露出一些缺点,例如比表面积小、光生电子-空穴对的复合率高和反应动力学差等.将体相g-C_3N_4剥离成g-C_3N_4纳米薄片是提高光催化效率的有效方法.薄层g-C_3N_4纳米片具有较高的比表面积,比体相的g-C_3N_4有更好的光生电子-空穴对分离效率.为了进一步提高g-C_3N_4的光催化性能,本文通过在薄层g-C_3N_4表面均匀分散Au纳米颗粒来控制电荷载流子的流动.并通过光催化产氢和污染物降解来评估金/薄层氮化碳(Au/monolayer g-C_3N_4)复合材料的光催化性能.所有的Au/薄层g-C_3N_4复合材料均显示出优于体相g-C_3N_4的光催化性能,其中1%Au/薄层g-C_3N_4复合光催化剂具有最高的产氢速率(565μmol g.1h.1),且具有最佳的污染物降解能力.这主要归结于热电子的注入,而不是肖特基结.Au纳米颗粒的成功引入带来了表面等离子共振(SPR)效应,SPR效应不仅能够提高光吸收效率,而且能够带来高效的热电子转移途径.热电子是从Au纳米颗粒表面注入到薄层g-C_3N_4纳米片的导带上.因此,Au/薄层g-C_3N_4复合光催化剂具有更高的光生电子-空穴对迁移和分离效率,以及更低的光生电子-空穴对复合几率.采用紫外可见光谱(UV-Vis)、光致发光光谱(PL)、光电流和阻抗等表征手段研究了Au/薄层g-C_3N_4复合光催化剂性能提升的原因.结果表明,相比于薄层g-C_3N_4纳米片,Au/薄层g-C_3N_4复合光催化剂具有更好的光电性能,因而光催化活性更高.此外,与薄层g-C_3N_4纳米片的光电流强度相比,Au/薄层g-C_3N_4复合光催化剂的光电流强度没有发生改变,这表明薄层g-C_3N_4纳米片导带上的光生电子不可能转移到Au纳米颗粒的表面.也就是说,肖特基结并没有参与到电子转移过程中。

Construction of a few-layer g-C_3N_4/α-MoO_3 nanoneedles all-solid-state Z-scheme photocatalytic system for photocatalytic degradation

The suppression of the recombination of electrons and holes(e–h) and the enhancement of the light absorption of semiconductors are two key points toward efficient photocatalytic degradation.Here,we report a few-layer g-C_3N_4/α-MoO_3 nanoneedles(flg-C_3N_4/α-MoO_3 NNs) all-solid-state Z-scheme mechanism photocatalyst synthesized via a typical hydrothermal method in a controlled manner.The recombination of the photo-induced e–h pairs could be effectively restrained by the Z-scheme passageway between the flg-C_3N_4 and α-MoO_3 NNs in the composite,which could also promise a high redox ability to degrade pollutants.And it became possible for the prepared photocatalyst to absorb light in a wide range of wavelengths.The detailed mechanism was studied by electron spin-resonance spectroscopy(ESR).The low-dimensional nanostructure of the two constituents(α-MoO_3 NNs with one-dimensional structure and flg-C_3N_4 with two-dimensional structure) endowed the composite with varieties of excellent physicochemical properties,which facilitated the transfer and diffusion of the photoelectrons and increased the specific surface area and the active sites.The 10 wt% flg-C_3N_4/α-MoO_3 NNs showed the best photocatalytic performance toward RhB degradation,the rate of which was 71.86%,～2.6 times higher than that ofα-MoO_3 NNs.

Influence of Cross-Sectional Flow Area of Annular Volute Casing on Transient Characteristics of Ceramic Centrifugal Pump

The annular volute is typically used in a slurry pump to reduce the collisions between solid particles and the volute tongue and to achieve a better resistance to blocking. However, only limited studies regarding annular volutes are available, and there is no systematic design method for annular volutes. In this study, the influence of volute casing cross-sectional flow area on the hydraulic loss, pressure pulsations, and radial force under varying working conditions in a centrifugal ceramic pump are discussed in detail. Experimental tests were conducted to validate the numerical results. The results indicated that, when the volute casing flow area increases, the hydraulic performance decreases marginally under the rated working conditions, but increases at the o-design points, specifically under large flow condition. However, the volute casing with a larger flow area has a wider high-e ciency region. In addition, the increase in the volute casing flow area will decrease the pressure pulsations in the volute, regardless of the working condition, and decrease the radial force on the shaft, therefore, providing an improved pump operational stability. It is anticipated that this study will be of benefit during the design of annular volutes.

Investigation on the Flow Behavior of Side Channel Pumps Based on Vortex Identification

The momentum flow exchange between the impeller and side channel produces highly turbulent flows in side channel pumps.The turbulent flows feature complex patterns of vortex structures that are partly responsible for the dissipation of energy losses and unsteady pressure pulsations.The concept of turbulent flows in side channel pumps requires a reliable vortex identification criterion to capture and predict the effects of the vortex structures on the performance.For this reason,the current study presents the application of the new Ω-criterion to a side channel pump model in comparison with other traditional methods such as Qand λ2 criteria.The 3D flow fields of the pump were obtained through unsteady Reynolds-averaged Navier-Stokes(RANS)simulations.Comparative studies showed that the Ω-criterion identifies the vortex of different intensities with a standard threshold,Ω=0.52.The Q and λ2 criteria required different thresholds to capture vortex of different intensities thus leads to subjective errors.Comparing theΩ-criterion intensity on different planes with the entropy losses and pressure pulsation,the longitudinal vortex plays an important role in the momentum exchange development which increases the head performance of the pump.However,the rate of exchange is impeded by the axial and radial vortices restricted in the impeller.Therefore,the impeller generates the highest entropy loss and pressure pulsation intensities which lower the output efficiency.Finally,the findings provide a fundamental background to the morphology of the vortex structures in the turbulent flows which can be dependent upon for efficiency improvement of side channel pumps.

α-Fe_2O_3 nanoplates with superior electrochemical performance for lithium-ion batteries

On account of the high theoretical capacity, high corrosion resistance, environmental benignity, abundant availability and low cost, the research on a-Fe_2O_3 has been gradually fastened on as promising anodes materials toward lithium-ion batteries(LIBs). A high-performance anode for LIBs based on α-Fe_2O_3 nanoplates have been selectively prepared. The α-Fe_2O_3 nanoplates can be synthesized with iron ionbased ionic liquid as iron source and template. The α-Fe_2O_3 nanoplates as the anode of LIBs can display high capacity of around1950 mAh g^(-1) at 0.5 A g^(-1) which have exceeded the theoretical capacity of α-Fe_2O_3. On account of unique nanoplate structures and gum arabic as binder, the α-Fe_2O_3 nanoplates also exhibit high rate capability and excellent cycling performance.

Bionics-Inspired Structure Boosts Drag and Noise Reduction of Rotating Machinery

As a global concern,environmental protection and energy conservation have attracted significant attention.Due to the large carbon emission of electricity,promoting green and low-carbon transformation of the power industry via the synergistic development of clean energy sources is essential.Rotating machinery plays a crucial role in pumped storage,hydropower generation,and nuclear power generation.Inspired by bionics,non-smooth features of creatures in nature have been introduced into the structure design of efficient rotating machines.First,the concept and classification of bionics are described.Then,the representative applications of non-smooth surface bionic structures in rotating machineries are systematically and comprehensively reviewed,such as groove structure,pit structure,and other non-smooth surfaces.Finally,conclusions are drawn and future directions are presented.The effective design of a bionic structure contributes toward noise reduction,drag reduction and efficiency improvement of rotating machineries.Green and ecological rotating machinery will remarkably reduce energy consumption and contribute to the realization of the“double carbon”goal.

Development status and trend of agricultural robot technology

In the face of the contradiction between the increasing demand for agricultural products and the sharp reduction of agricultural resources and labor force,agricultural robot technology is developing explosively on the basis of decades of technical and industrial exploration.In view of the complexity and particularity of the development of agricultural robot technology,it is of great value to summarize its development characteristics and make reasonable judgments on its development trend.In this paper,the type of agricultural robot systems was first discussed.From the classification of agricultural robot systems,the development of main types of monitoring robots,non-selective and selective working robots for crop farming,livestock and poultry farming and aquaculture were introduced in detail.Then the scientific research,core technology,and commercialization of different types of agricultural robots were summarized.It is believed that navigation in complex agricultural environments,damage-free robot-crop interaction,and agronomy-robot fusion have high scientific value and significance to promote the revolutionary advances in agricultural robot technology.The characteristics of inter-discipline between agricultural robot technology and new materials,artificial intelligence,bionics,agronomy are research focus.The fast damage-free operation,autonomous navigation for complex environments,target detection for complex backgrounds,and special design for agricultural robots are considered to be the key technology of agricultural robot development,and the development path is given.Finally,robot-crop interaction simulation,big data support,and artificial intelligence are regarded as paths to realize the breakthrough of key agricultural robot technologies.The summary and prospect of this paper are of positive significance to promote the overall development of agricultural robot technology.

Review of air disturbance technology for plant frost protection

Confronted with severe frost damage to plants,methods,technologies and equipment have been developed and applied during the past century.The paper presents a comprehensive review on the most effective and active technology to protect plants from radiation frost based on air disturbance technology.The working principle of the technology was elaborated with frost protection mechanism,structures and applicability of three types of working patterns:conventional wind machines,selective inverted sink and portable vertical blowing.As an automatic mechanized technology,control strategy,applicable occasion and proper parameters are introduced for each type of working pattern.The operation of the technology and equipment depends on plant critical temperature,prevailing climatic conditions,thermal inversions strength,as well as costs.The frost protection performance and effectiveness of conventional horizontal wind machines,selective inverted sinks and helicopters are discussed and compared from the cost-effectiveness and application aspects,and the feasibility of selective inverted sinks is still controversial.Therefore,conventional wind machines are the best choice for plant frost protection and consequently are widely used in temperate and subtropical areas throughout the world.The frost protection application with helicopters is not easy to use during the frost nights with high cost.The paper also provides researchers with some perspectives on improving air disturbance technology and its equipment,and some practice recommendations for growers.

Performance experiment and numerical prediction on the optimization design of the micro-sized water turbine for the hose reel irrigator

In order to significantly improve the efficiency of driving water turbine used in hose reel irrigator,a new water turbine structure was proposed by the method of performance test and numerical calculation.The internal flow characteristics of original water turbine were analyzed,and it was found that unreasonable design of main flow passage components such as inlet,outlet and runner could not effectively translated pressure energy of upper stream into impact kinetic energy of blade,and gave rise to low energy conversion efficiency of water turbine.The inadequate internal flow and uneven pressure distribution were also not conducive to energy conversion efficiency.Then a new structure of water turbine structure was presented,in which the inlet has a tangential nozzle jet and the outlet is in axial direction.The computational analysis showed that the nozzle jet at the inlet of the new water turbine runner,which makes jet flow mainly concentrate in the impacted blade passage,can reduce the loss of flow kinetic energy.The axial outflow increases the distance of inflow in the runner,which is more conducive to the runner blades work.Performance experiments on both original and new water turbines showed that the highest efficiency of the new turbine is almost 20 percentages higher than that of the original turbine,and the new turbine is nearly triple output power over the original turbine.The internal flow characteristic analysis and the performance experiment were conducted to assess the feasibility of the replacement of the original water turbine by the new water turbine.

Numerical simulation of particle motion at cucumber straw grinding process based on EDEM

Simulation of straw grinding process based on discrete element method(DEM)was proposed.According to the force analysis and kinematics analysis,the differential equation of straw particle motion on hammers was deduced,and the formation mechanism of the material circulation layer was obtained.Geometric model of grinder,particle model and contact model were established by EDEM software.The influence of hammer number,hammer thickness and gap of the hammer-sieve on particle grinding number and power consumption were obtained by single factor simulation test.The grinding process is divided into three stages.The hammer smashing plays a dominant role in 0-0.25 s.While the hammer smashing particle number increases slowly and then decreases to the lowest level in 0.25-0.60 s,the tooth plate smashing particle number increases rapidly and dominates,and then forming a material circulation layer.The hammer and tooth plate smashing particle number is basically stable in 0.60-2.00 s,and the tooth plate smashing occupies the dominant position.With the increase of the number and thickness of hammers,the power consumption of crusher tends to increase,and with the increase of the gap between hammers and sieves,the power consumption of crusher decreases first and then increases.The results can provide guidance for the development of high-efficiency and energy-saving grinding equipment for cucumber straw.

Comparison of droplet distributions from fluidic and impact sprinklers

To adapt to the trend toward low-energy precision irrigation, the droplet distributions for two new prototype sprinklers, outside signal sprinkler(OS) and fluidic sprinkler(FS), were compared with impact sprinkler(IS). A laser precipitation monitor was used to measure the droplet distributions. Droplet size and velocity distributions were tested under four operating pressures for nozzles 1.5 m above the ground. For the operating pressures tested, the mean OS, FS and IS droplet diameters ranged from 0 to 3.4, 0 to 3.5, 0 to 4.0 mm, respectively.The mean OS and FS droplet velocities ranged from 0 to6.3 m$s–1, whereas IS ranged from 0 to 6.3 m$s–1. Being gas-liquid fluidic sprinklers, droplet distributions of the OS and FS were similar, although not identical. IS mostly produced a 0.5 mm larger droplet diameter and a 0.5 m$s–1greater velocity than OS and FS. A new empirical equation is proposed for determination of droplet size for OS and FS, which is sufficiently accurate and simple to use. Basic statistics for droplet size and velocity were performed on data obtained by the photographic methods. The mean droplet diameter(arithmetic, volumetric and median)decreased and the mean velocity increased in operating pressure for the three types of sprinkler.

Irrigated agriculture for food self-sufficiency in the sub-Saharan African region

Increasing agricultural productivity in Africa will have important impacts not only on the agricultural sector but also can be a catalyst for industrialization through agro-processing.Irrigation,therefore,has a crucial role in enhancing food security and reducing hunger in the region.Numerous countries in Africa consider water and irrigation management as a key factor in improving their food security and ensuring access to drinking-water for their populations.Fortunately,there is evidence from a number of places on the continent where the adoption of efficient irrigation systems has led to higher productivity among smallholder farmers.While the appropriate interventions for the diverse agro-ecological zones of sub-Saharan Africa are known,adoption among smallholder farmers still remains a challenge.Digital technology opens the vast untapped potential for farmers,investors,and entrepreneurs to improve the efficiency of food production and consumption in Africa.From precision farming to an efficient food supply chain,technology could bring major economic,social,and environmental benefits.Increasing investment and involvement of the private sector is crucial for the up-scaling of irrigation technologies.Indeed,the sheer optimism across the startup ecosystem is that extreme hunger can be cured in Africa,in this generation,by significantly transforming the industry that employs most of its citizens.This paper draws on lessons from past trends in the irrigation industry and emphasizes on novel directions to ensure that farmers,as well as other stakeholders reap the benefits associated with improved technologies.