A two-dimensional air streamer discharge model based on the improved Helmholtz equation at low temperature and sub-atmospheric pressure

In this paper,an efficient boundary condition is applied to solve the photoionization rate,and a two-dimensional numerical simulation is carried out for the development and propagation of an air streamer at low temperature and sub-atmospheric pressure.The results show that the new boundary condition improves the calculation accuracy,but the influence of photoionization on the streamer discharge process is not obvious.The discharge current in the development of streamer discharge is defined,and the corresponding expression of the positive and negative streamer discharge current is given.The influence of the electric field exceeding the threshold value on the discharge process is preliminarily introduced.In the process of discharge,only the propagation velocity of the streamer is obviously higher than that of normal temperature and pressure,and the trend of the other parameters is basically the same as that described in the previous paper.The above results give us a deeper understanding of the discharge characteristics under low temperature and sub-atmospheric pressure,which has certain significance for the development of aviation and high voltage engineering.

Effect of aeration on fast gas pressure tests

Given the problem of the long time required for testing gas pressure, we propose a fast-test method in which we used a technique of fast borehole sealing and air replenishing. Based on the characteristics of gas emission from boreholes to be tested, we built a theoretical model for calculating parameters during the process of increasing natural pressure and aeration. Using this model, we investigated the effect of different aeration conditions on velocity of pressure tests. The result shows that: 1) aerating air into boreholes can speed up gas pressure tests and 2) the more similar the pressure of the aerated air to the original gas pressure, the smaller the gas volume absorbed by coal and the shorter the time needed in pressure test. A case study in the Lu’an mining area shows that the time needed for gas pressure test is only 4 h using our method of aeration and 29 h under conditions of increasing natural pressure, saving time by 86.2%. This case study also indicates that, by using the aeration method, only one hour is needed for gas pressure to reach a stable state, which breaks the record of the shortest time needed for gas pressure tests in China.

3D numerical simulation of high pressure squeezing process with revised Drucker-Prager/Cap model

In order to investigate the sand mold strength after the aeration sand filling-high pressure squeeze moldingprocess,a tree-dimentional(3D)numerical simulation was introduced.The commercial finite element method(FEM)software ABAQUScombined with a revised Drucker-Prager/Cap model was used to simulate the squeeze compaction process.Additionally,the sand bulk density after the aeration sand filling process was tested by a specially designed experiment,which divided the whole sand bulk in the molding chamber into5x9regions and it was used as the input to simulate the squeeze process.During the simulation process,the uniform modeling simulation and the patition modeling simulation methods were used a d the3D numercal simulation results were compared with correlative benchmark testings.From the3D numerica simulation results,it can be concluded that the uniform sand bulk density distribution can obtain a high quality sandmold and the revised Drncker-Pager/Cap model is suitable for handling the situation with the complex paaern.The3D numerical simulation results can predict well the sand mold strength distribution and can be used as guidelines for the production practice.

基于水气两相模拟的薄水舌、大落差水力特性分析及结构影响分析

对高拱坝深孔小开度泄流时,薄水舌、大落差条件下的水力特性及对水垫塘底板结构影响进行分析。通过水力学规范公式、刘培清等人总结的经验公式对不考虑空气阻力、掺气作用时的临底水力特性进行分析;并考虑水气两相作用,采用数值模拟方法对比研究薄水舌、大落差条件下,空气对水舌的阻力及掺气作用,分析临底水力特性及结构影响,为通过坝身孔口实现水垫塘反充水的思路提供支撑,为类似研究和工程应用提供借鉴和参考。

负压差斜管内催化剂颗粒流动特性的实验研究

在规格为Φ150 mm×3600 mm的负压差斜管-阀门实验装置上,通过测量和分析不同催化剂颗粒质量流率(G_(s))时斜管内轴向动态压力的特征参数,进行催化裂化装置斜管内催化剂颗粒的流动特性研究。结果表明:斜管蓄压能力随G_(s)的增大而增大,管内依次出现稀相分层流、密相分层流和填充流;斜管内的压力分布、主频、幅值、标准偏差与流态相对应,可用于流态的量化识别;当G_(s)=65.96 kg/(m^(2)·s)时,斜管内存在多流态,分别为过渡填充流、填充流、密相流;在斜管中部通入松动风,可以有效改善颗粒输送能力和斜管蓄压能力。

膜曝气生物膜反应器脱氮性能研究

膜曝气生物膜反应器(MABR)有效地将生物膜法技术和膜分离技术结合在一起,在污水脱氮方面潜力巨大。以MABR处理模拟生活污水和豆制品加工废水,着重考察了MABR的稳定性及脱氮性能。结果表明,在HRT=12 h、曝气压力=10 kPa和C/N=5时,MABR对模拟生活污水处理效果最佳,COD、氨氮、TN的平均去除率分别为92.0%、86.5%、83.3%。而在HRT=8 h和曝气压力=10 kPa时,MABR对豆制品加工废水处理效果最佳,COD、氨氮、TN的容积负荷分别为1320、125.5、184 g(/m^(3)·d),平均去除率分别可达到84.2%、81.5%、79.7%,优于传统生物膜法脱氮。

膜曝气生物膜反应器处理合流制溢流污水的实验研究

以聚丙烯复合材料经熔融拉伸制成的帘式超薄微孔中空纤维膜为载体,构建膜曝气生物膜反应器装置处理合流制溢流污水,研究在不同水力停留时间、曝气压力、水流流速条件下,膜曝气生物膜反应器对水体中污染物COD、NH_(4)^(+)-N、TN的去除率。结果表明:膜曝气生物膜反应器对水体中各项污染物均有较好去除效果。水力停留时间为12 h时,COD、NH_(4)^(+)-N、TN去除效果较好,去除率分别为80.8%、82.4%、65.4%;水力停留时间为8 h时,TP去除效果达到34.2%,后期逐渐趋于平缓。溶解氧浓度随曝气压力增加而增加,曝气压力达到25 kPa之后COD、NH_(4)^(+)-N达到较佳的去除率,平均去除率分别为82.2%、84.1%;而TN去除的最佳曝气压力为15 kPa,去除率为70.0%。水流流速为0.03 m/s和0.05 m/s时,反应器整体运行效果较好,对COD、NH_(4)^(+)-N、TN的平均去除率分别为81.8%、83.5%、67.8%。

铁尾矿基蒸压加气混凝土低温蒸压技术研究

为了实现铁尾矿的综合利用,优化铁尾矿蒸压加气混凝土的生产成本,针对铁尾矿蒸压加气混凝土蒸养压力高、制品抗压强度低等问题,以铁尾矿作为主要原料,结合工业生产探究了外加剂、废浆、胶凝材料等因素对制品性能的影响。研究结果表明:外加剂、废浆及胶凝材料能显著改善铁尾矿蒸压加气混凝土制品的性能,通过掺入外加剂,可使蒸压加气混凝土的蒸养压力从1.2 MPa降至0.9 MPa;在铁尾矿、废浆、水泥、石灰、石膏、外加剂配比为50%∶20%∶18%∶6%∶4%∶2%时,可制备出干密度603.59 kg/cm^(3)、抗压强度3.67 MPa的铁尾矿蒸压加气混凝土制品,可实现铁尾矿的高效综合利用。

Experimental study on pressure and aeration characteristics in stepped chute flows

The free flow on the step surfaces has received much attention for its representative body type,flow structure,water-air two phase flow,cavitation,and many complex issues.The experiments about the time-averaged pressure and aeration concentration distribution on the step surface show that the vertical plane of steps will inevitably experience negative pressure,which must rely on adequate aeration concentration to avoid cavitation damage.However,the self-aerated flow at the head section has a relatively low aeration concentration,and the concentration of the entire steps decreases with the increasing of weir head,the minimum appears in the vicinity of the corner,and the location is close to the minimum pressure.Thus,it is necessary to set aerator in the upstream end of the step surfaces to avoid cavitation damage.

AN EXPERIMENTAL INVESTIGATION OF PRESSURE AND CAVITATION CHARACTERISTICS OF HIGH VELOCITY FLOW OVER A CYLINDRICAL PROTRUSION IN THE PRESENCE AND ABSENCE OF AERATION

This article experimentally investigated the pressure and cavitation characteristics of high velocity flow over a surface irregularity with and without aeration in a non-circulating water tunnel system. The surface irregularity is a cylindrical protrusion made of stainless steel of 6 mm diameter and 2 mm height. Pressures with and without aeration were measured with MPX400D pressure transducers and real-timely acquired by a SINOCERA YE6263 data acquisition system. Variations in flow regimes with and without aeration were observed. Pressure profiles and their variations with air concentration upper and lower cylindrical protrusion on the invert and obvert walls were determined. Variations of cavitation number with air concentration lower cylindrical protrusion were analyzed. Also, cavitation numbers in the presence and absence of aeration were compared.

Theoretical Model of Dynamic Bulk Modulus for Aerated Hydraulic Fluid

Existing models of bulk modulus for aerated hydraulic fluids primarily focus on the effects of pressure and air fraction,whereas the effect of temperature on bulk modulus is disregarded.Based on the lumped parameter method and the full cavitation model,combined with the improved Henry’s law and the air polytropic course equation,a theoretical model of dynamic bulk modulus for an aerated hydraulic fluid is derived.The effects of system pressure,air fraction,and temperature on bulk modulus are investigated using the controlled variable method.The results show that the dynamic bulk modulus of the aerated hydraulic fluid is inconsistent during the compression process.At the same pressure point,the dynamic bulk modulus during expansion is higher than that during compression.Under the same initial air faction and pressure changing period,a higher temperature results in a lower dynamic bulk modulus.When the pressure is lower,the dynamic bulk modulus of each temperature point is more similar to each other.By comparing the theoretical results with the actual dynamic bulk modulus of the Shell Tellus S ISO32 standard air-containing oil,the goodness-of-fit between the theoretical model and experimental value at three temperatures is 0.9726,0.9732,and 0.9675,which validates the theoretical model.In this study,a calculation model of dynamic bulk modulus that considers temperature factors is proposed.It predicts the dynamic bulk modulus of aerated hydraulic fluids at different temperatures and provides a theoretical basis for improving the analytical model of bulk modulus.

Combustion performance studies of aluminum and boron based composite solid propellants in sub-atmospheric pressure regimes

The aim of present study is to investigate the burning rate,ignition delay,and flame characteristics of ammonium perchlorate(AP)-hydroxyl terminated poly-butadiene(HTPB)[AP/HTPB]based composite propellants(CSP's)in sub-atmospheric pressure regimes(13 kPae100 kPa).Several fuels and catalyzed were used to evaluate their effects on the combustion characteristics of AP based propellants in sub-atmospheric pressure regimes.In fuels,aluminum(Al)and boron(B)were selected as metallic and non-metallic fuel respectively.While in catalyst,butyl ferrocene(B.F.)and ferric oxide(F.O.)were selected as liquid and solid catalyst respectively.Apart from these,other ingredients that were used are di-octyl adipate(DOA),toluene di-isocyanate(TDI),and glycerol.The article throws some light on the burning rate and ignition delay properties for these new classes of prepared propellant samples.At subatmospheric pressures,all propellants are susceptible to irregular burning with the ejection of soot's,fumes,and unburned particles.F.O.based catalyzed propellants can sustain its combustion up to the lowest pressure.

PRESSURE CHARACTERISTICS OF CAVITATION CONTROL BY AERATION

This experimental investigation was systernatically conducted with the aid of a non-circulating water tunnel in the Hydraulics Laboratory at Zhejiang University of Tech nology in China, The test velocity is between 20m/s and 40m/ s. The least air concentration to prevent cavitation erosion lies between 1. 7% and 4. 5%. Pressure waveforms with and without aeration in cavitation and cavitation erosion regions were measured. Time-averaged pressure profiles with and without aeration were compared. Pressure characteristics cotresponding to least air concentration to prevent cavitation erosion in cavitation and cavitation erosion regions were analyzed.

填埋场单井注气气体压力监测试验及预测模型

确定填埋场注气过程中气体压力分布特征可为好氧通风工程提供关键技术和理论支撑。以现场单井注气试验为依托,在渗流力学理论的基础上,开展了不同注气强度条件下气体压力分布监测试验,分析了注气过程中气体压力的径向分布特征,推导了注气条件下垃圾土体内部以解析解形式表达的气体压力预测(analytical gas pressure prediction,简称AGPP)模型;结合现场气体压力监测结果,构建了以注气井压力为核心参数的经验公式形式的气体压力预测(empiricalgaspressure prediction,简称EGPP)模型。试验结果表明:低压注气强度也可以达到良好的注气效果,在较短时间内可以让气体充满注气井周围;通过现场监测数据与AGPP模型、EGPP模型的对比,初步验证了两种模型的可靠性。以上成果为预测和评估好氧通风过程中垃圾填埋场气体压力分布提供了新方法。

梯形消能墩—台阶组合式消能工水力特性研究

为降低台阶负压,减少空化空蚀的影响,提高台阶消能效果,在传统台阶凸角位置增设梯形消能墩组成梯形消能墩—台阶组合式消能工,采用水工模型试验与数值模拟相结合的方法,研究梯形消能墩—台阶组合式消能工的水力特性。结果表明,梯形消能墩—台阶组合式消能工台阶水平面与竖直面在靠近凸角附近存在负压,有发生空化空蚀破坏的可能;但台阶水平面与竖直面负压区掺气浓度基本大于5%,可有效降低空化空蚀危害;在本研究范围内,梯形消能墩—台阶组合式消能工消能率可达70%以上,消能率随流量的增大而降低。该组合式消能工有利于减小台阶空化空蚀危害和提高台阶消能效果,可为台阶消能工设计和现有台阶溢洪道除险加固提供参考依据。

不同曝气压力下MABR反应器污染物去除效率研究

通过膜曝气生物膜反应器处理医院污水中试实验研究,对比不同曝气压力下MABR池溶解氧浓度变化,以及不同压力下COD、氨氮和总氮的去除效果变化情况,探索MABR工艺处理医院污水的启动挂膜及最佳运行参数。结果表明:采用低曝气压力和A^(2)O循环挂膜方式启动,MABR工艺能在40天内实现膜表面快速挂膜。MABR池中溶解氧浓度随曝气压力的增加而增加;曝气压力变化对COD去除率影响较小,前期成正比例缓慢增加,后期逐渐趋于平缓;曝气压力对氨氮去除效果成正相关,随着曝气压力持续升高,氨氮去除率出现明显增加趋势;随着曝气压力的增加去除总氮的效果前期呈缓慢增长趋势,压力超过25 kPa时总氮去除效率反而下降,曝气压力过高成为反硝化脱氮的制约因素。中试研究表明:MABR工艺在压力为25 kPa和HRT为12 h情况下运行效果较好,该工艺适用于医院污水处理领域。

弧面对压法检测蒸压加气混凝土抗压强度技术研究

为提高蒸压加气混凝土抗压强度检测效率,提出了一种弧面对压法检测技术。选取A1.5~A5.0共5个强度级别的蒸压加气混凝土砌块钻取直径38mm的芯样作为弧面对压试件,采用自行研制的专用设备在弧面对压试件侧面进行抗压试验;同时在与钻取弧面对压试件相邻的部位切制边长为100mm的立方体试块,测试其抗压强度值;建立了弧面对压试件破坏荷载与立方体试件的抗压强度间关系。依据最小二乘法原理对试验数据进行回归,拟合得到弧面对压法检测蒸压加气混凝土测强公式。最后,从全国范围内随机选取5个厂家的不同强度级别的蒸压加气混凝土砌块作为验证材料,进行了弧面对压法与传统立方体试块测试法的对比;结果表明,弧面对压法的试验用时比传统立方体试块测试法明显缩短,且测强曲线具有较高的测试精度。

Experimental and Numerical Investigations on Ignition and LBO Performances for Staged Combustor under Sub-Atmospheric Conditions

In order to effectively widen the high-altitude operating limits of the multi-swirl staged combustor,the ignition and lean blow-out(LBO)performances of the model combustor were experimentally acquired under the conditions of room temperature and sub-atmospheric pressure with the altitude ranging from 0 km to 12 km.Moreover,the isothermal flow fields inside a staged model combustor with different sub-atmospheric conditions were simulated.Experimental results show that the minimum ignition and LBO fuel-air ratio(FAR)increase rapidly with the increase of simulated altitude.In addition,as the relative pressure drop of injector increases from1%to 3%,the ignition and LBO performances are gradually improved.Side visualization of the flame by high-speed camera shows that the time-averaged flames under stable combustion have a similar distribution pattern under different pressure drops.The luminous intensity is stratified into dim-bright-dim layers along axial direction.The flame near LBO shrinks to the outlet of pilot stage with a great reduction in luminous intensity.The numerical results reveal that with the decrease of air pressure,the air mass flow rate involved in atomization and combustion is significantly reduced,and the aerodynamic shear force of swirling air is weakened,which are adverse to atomization and fuel-air mixing for airblast atomizer and further lead to the deterioration of ignition and LBO performances.

Experimental Analysis of Pressure Fluctuations behind a Bottom Aerator

Experimental observations show that the random process of two phase flow behind an aerator is an ergodic process and its amplitude distribution is similar to a normal distribution. The maximum pressure fluctuation is at the re attachment point where the jet trajectory flow over the aerator re attaches to bottom of the channel, and its amplitude is 2 3 times larger than when there is no aerator. There is a dominant frequency of 1 24 Hz in the model, but the coherence in the frequency domain is not obvious for other frequencies beside the dominant frequency. There is a large vortex at the re attachment point behind the aerator but correlation among the measurement points is not obvious in the time domain.

降低次氧化锌氟含量生产实践

安徽铜冠有色金属(池州)有限责任公司三连炉于2018年改造投产,其中烟化炉产出的次氧化锌经浆化、碱洗脱氟处理后转移给锌冶炼原料,形成了独特的铅锌联动生产模式。主要介绍采取调整曝气压力、碱洗温度、物料颗粒大小等方式降低次氧化锌氟含量。