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.

Numerical simulation of acoustic pressure field for ultrasonic grain refinement of AZ80 magnesium alloy

Ultrasound with different intensities was applied to treating AZ80 alloy melt to improve its solidification structure.The average grain size of the alloy could be decreased from 303 to 148 μm after the ultrasound with intensity of 30.48 W/cm2 was applied.To gain insight into the mechanism of ultrasonic treatment which affected the microstructure of the alloy,numerical simulations were carried out and the effects of different ultrasonic pressures on the behaviors of cavitation bubble in the melt were studied.The ultrasonic field propagation in the melt was also characterized.The results show that samples from different positions are subjected to different acoustic pressures and the effect of grain refinement by ultrasonic treatment for these samples is different.With the increase of ultrasonic intensity,the acoustic pressure is increased and the grain size is decreased generally.

Refinement and strengthening mechanism of Mg−Zn−Cu−Zr−Ca alloy solidified under extremely high pressure

Mg−Zn−Cu−Zr−Ca samples were solidified under high pressures of 2-6 GPa.Scanning electron microscopy and electron backscatter diffraction were used to study the distribution of Ca in the microstructure and its effect on the solidification structure.The mechanical properties of the samples were investigated through compression tests.The results show that Ca is mostly dissolved in the matrix and the Mg_(2)Ca phase is formed under high pressure,but it is mainly segregated among dendrites under atmospheric pressure.The Mg_(2)Ca particles are effective heterogeneous nuclei ofα-Mg crystals,which significantly increases the number of crystal nuclei and refines the solidification structure of the alloy,with the grain size reduced to 22μm at 6 GPa.As no Ca segregating among the dendrites exists,more Zn is dissolved in the matrix.Consequently,the intergranular second phase changes from MgZn with a higher Zn/Mg ratio to Mg7Zn3 with a lower Zn/Mg ratio.The volume fraction of the intergranular second phase also increases to 22%.Owing to the combined strengthening of grain refinement,solid solution,and dispersion,the compression strength of the Mg-Zn-Cu-Zr-Ca alloy solidified under 6 GPa is up to 520 MPa.

Grain refinement and mechanical properties improvement of casting A357 alloy by high pressure differential pressure casting process

By using conventional differential pressure casting process and high pressure differential pressure casting process respectively, Al-Si-Mg system A357 alloy castings were produced. The results show that compared with the conventional differential pressure casting process, the high pressure differential pressure casting process can further refine grain and improve the tensile strength and elongation of as-cast and heat treated A357 alloy. For as-cast A357 alloy with SiO2 resin sand mould, the increasing scales exceed 6% and 50%, respectively. After heat treatment, the increasing scales exceed 15% and 50% respectively. For as-cast A357 alloy with SiO2-Fe chill mould, the increasing scales exceed 6% and 17% respectively. After heat treatment, the increasing scales exceed 7% and 23% respectively. But the increasing scale depends on the cooling rate of casting. With the increase of the cooling rate, the increasing scale decreases.

Effect of Refining Parameters on Medium Density Fibreboard (MDF) Properties from Oil Palm Trunk

The properties of medium density fibreboard (MDF) made from oil palm trunk (OPT) as affected by refining pressure and preheating time were investigated. The OPT chips were refined in the MDF pilot plant by using four refining pressures (2, 4, 6 and 8 bar) and four different preheating time (100, 200, 300 and 400 seconds). The refined fibres were blended with 10% of urea formaldehyde with a board target density of 720 kg/m3. MDF boards were evaluated based on European Standard EN 622-5:2006 for thickness swelling (TS), internal bonding (IB), modulus of rupture (MOR) and modulus of elasticity (MOE). Analysis of variance (ANOVA) was used to analyze the significance of the factors. The results from this study indicated that refining pressure and preheating time are significant factors for all MDF properties. Low refining pressure and preheating time produced higher TS, lower MOR and MOE with poor bonding than those boards prepared from fibres refined at higher refining pressure and longer preheating time. OPT fibre treated with 8 bar produced good swelling resistance but detrimental on mechanical properties of the finish board. 6 bar steam pressure offered the highest value of mechanical properties (MOE, MOR and IB). Boards from intermediate refining condition (6 bar and 300 seconds) were found the better board properties having 14.58%, 0.73 N/mm2, 38 N/mm2 and 3597 N/mm2 for TS, IB, MOR and MOE respectively.

Microstructure evolution and dislocation configurations in nanostructured Al-Mg alloys processed by high pressure torsion

Microstructure evolution and dislocation configurations in nanostructured Al–Mg alloys processed by high pressure torsion （HPT） were analyzed by transmission electron microscopy （TEM） and high-resolution TEM （HRTEM）. The results show that the grains less than 100 nm have sharp grain boundaries （GBs） and are completely free of dislocations. In contrast, a high density of dislocation as high as 1017 m^-2 exists within the grains larger than 200 nm and these larger grains are usually separated into subgrains and dislocation cells. The dislocations are 60° full dislocations with Burgers vectors of 1/2〈110〉and most of them appear as dipoles and loops. The microtwins and stacking faults （SFs） formed by the Shockley partials from the dissociation of both the 60° mixed dislocation and 0° screw dislocation in ultrafine grains were simultaneously observed by HRTEM in the HPT Al–Mg alloys. These results suggest that partial dislocation emissions, as well as the activation of partial dislocations could also become a deformation mechanism in ultrafine-grained aluminum during severe plastic deformation. The grain refinement mechanism associated with the very high local dislocation density, the dislocation cells and the non-equilibrium GBs, as well as the SFs and microtwins in the HPT Al-Mg alloys were proposed.

Effect of titanium content on the refinement of coarse columnar austenite grains during the solidification of peritectic steel

The effect of titanium content on the refinement of austenite grain size in as-cast peritectic carbon steel was investigated by fast directional solidification experiments with simulating the solidification and growth of surface and subsurface austenite in continuously cast slabs.Transmission electron microscope(TEM)and scanning electron microscope(SEM)were used to analyze the size and distribution of Ti(C,N)precipitates during solidification.Based on these results,the pinning pressure of Ti(C,N)precipitates on the growth of coarse columnar grains(CCGs)was studied.The results show that the austenite microstructure of as-cast peritectic carbon steel is mainly composed of the regions of CCGs and fine columnar grains(FCGs).Increasing the content of titanium reduces the region and the short axis of the CCGs.When the content of titanium is 0.09wt%,there is no CCG region.Dispersed microscale particles will firstly form in the liquid,which will decrease the transition temperature from FCGs to CCGs.The chain-like nanoscale Ti(C,N)will precipitate with the decrease of the transition temperature.Furthermore,calculations shows that the refinement of the CCGs is caused by the pinning effect of Ti(C,N)precipitates.

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.

Grain-refining fabrication of nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy ceramics by ultra-high pressure sintering

As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low thermal conductivity.However,the low sintering ability limits its application in thermal barrier coating and radioactive waste immobilization.It usually needs long-term high-temperature soaking to achieve full density,but with inevitable grain growth.In this work,dense and grain-refined nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramics were prepared with ultra-high pressure sintering(UHPS)method under 10 GPa at a low temperature of 800℃.The densification behavior,microstructure evo-lution,and properties of the UHPS-ed samples were then investigated.The grain size of as-prepared(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramic was only 151 nm,which is 40%smaller than that of raw pow-der.In addition,it exhibited advantageous properties including both high hardness and aqueous durabil-ity.Plastic deformation under ultra-high pressure was believed as the dominant densification mechanism responsible for grain refinement and property improvement.

糠醛精制装置工艺优化降低抽出油溶剂含量

糠醛精制装置受糠醛结焦温度所限,抽出油回收系统经三效蒸发后,汽提塔底温度难以进一步提高。在加工高芳烃原料时,因溶剂对芳烃溶解性好,产品抽出油溶剂含量高。采用抽出液二次加热的方法可以提高抽出油汽提塔底温度,对降低抽出油溶剂含量效果较好。通过模拟计算得出安装抽出液二次加热器的最优位置,推荐设置在三效蒸发塔与闪蒸塔之间,相比无二次加热可以降低抽出油溶剂含量约83.1%。计算得出汽提塔最优汽提蒸汽用量为塔底抽出油量的5%,汽提塔顶温度和汽提塔底抽出油溶剂含量近似成反比关系,但汽提塔顶温度的提高需要注意塔顶气中携带油的影响。小负荷运行或者设计加工量较小的装置,通过设置抽出油循环流程,可提高汽提塔底温度,有利于降低汽提塔底溶剂含量。通过设置抽出油二次加热、抽出油循环流程,优化汽提塔操作压力、塔顶温度、汽提蒸汽量等,实际运行可以将抽出油溶剂质量分数控制在小于150μg/g,降低了装置溶剂消耗。

精细化护理对剖宫产术后发生压疮患者的干预效果研究

目的分析基于精细化护理对剖宫产术后发生压疮患者的干预效果。方法将2021年6月至2022年6月就诊于焦作市妇幼保健院的120例剖宫产术后发生压疮患者采用抓阄法分为常规组与观察组,各60例。观察组行精细化护理的护理干预,常规组行常规护理干预,对比两组干预前后负性情绪、疼痛程度、自我效能、睡眠质量、遵医依从度及满意度。结果干预后,两组负性心理情绪对比均有所降低,且观察组低于常规组,差异有统计学意义(P<0.05)。干预后,两组在疼痛程度评分均有所降低,且观察组低于常规组,差异有统计学意义(P<0.05)。干预后,两组自我效能评分均有所提升;且观察组高于常规组,差异有统计学意义(P<0.05)。观察组失眠症状改善率(96.67%)明显高于对照组(78.33%),差异有统计学意义(P<0.05)。观察组遵医依从度方面高于常规组,差异有统计学意义(P<0.05)。观察组满意度(98.33)高于常规组(88.33),差异有统计学意义(P<0.05)。结论基于精细化护理可改善剖宫产术后发生压疮患者疼痛程度、负性情绪,提高遵医依从度,降低疼痛程度,效果理想。

Aspen Plus模拟热耦合变压汽提工艺优化糠醛精制装置脱水塔

糠醛精制装置脱水塔一般采用单塔汽提工艺,由于脱水塔塔顶温度和压力较低,常规技术无法较好地回收塔顶气热量。运用Aspen Plus软件,基于NRTL热力学模型对脱水塔系统进行模拟计算,根据共沸温度的变化确定采用热耦合变压汽提工艺的可行性。对比分析常规汽提工艺和热耦合变压汽提工艺,以年总费用(C_(TA))作为评价指标,同时考虑降低一次投资,优化了热耦合变压汽提工艺低压塔和高压塔的塔板数、高压塔的操作压力等参数,推荐低压塔理论塔板数设置为4,高压塔理论塔板数设置为8,高压塔操作压力在230~305 kPa之间。与常规单塔汽提工艺相比,热耦合变压汽提工艺设备总成本增加32.1%,年运行费用减少28.1%,C_(TA)减少22.9%,热耦合变压汽提工艺具有较明显的经济优势。

炼油化工设备的带压堵漏技术的应用研究

随着我国工业的快速发展,炼油化工行业在国民经济中的地位越来越重要。然而,炼油化工设备在长期运行过程中经常会出现各种泄漏问题,这不仅影响生产效率,还会对环境造成严重污染。因此,采取有效的堵漏技术对保障生产安全和环境保护具有重要意义。炼油化工设备的带压堵漏技术是保障生产安全和环境保护的重要手段。随着技术的不断进步和应用需求的增长,带压堵漏技术在未来将会得到更广泛的应用和发展。因此,详细介绍了炼油化工设备的带压堵漏技术,并分析了其应用现状与发展前景。

驻波压力场速度波腹位置射流雾化的数值模拟

为研究驻波压力场速度波腹位置射流的雾化特性,基于八叉树结构形式的网格自适应方法与多尺度仿真算法构建了射流雾化的数值模拟方案,通过在计算域边界施加扰动构建了一阶横向驻波压力场。在此基础上实现了振荡压力场与雾化的多物理场耦合计算,研究了驻波压力场速度波腹位置射流雾化的响应特性,基于气体动力学理论阐述了速度波腹位置射流雾化的响应机理。结果表明:基于自适应网格与多尺度仿真算法建立的雾化数值模拟方案可以实现雾化过程较为准确的求解,是研究雾化过程的有力工具;反压振荡与雾化的耦合求解算法可以研究振荡压力场下的雾化特性,对于进一步认识非定常雾化特性并揭示热声耦合机理起到重要的作用;射流处于速度波腹位置时,圆柱射流发生变形变成扁平液膜,并伴随气流的运动发生周期性摆动,破碎长度减小,破碎程度加剧。

精细化在“111”产品质量提升中的应用

在内蒙古某“CO_(2)+O_(2)”地浸铀矿山引入精细化管理模式,对影响产品质量的吸附、淋洗、酸化沉淀等工序进行精细管理。淋洗剂配制由“沉降母液+碳酸氢钠+盐酸+氯化钠”优化为“沉降母液+碳酸氢钠+清水”,维持淋洗剂pH为9.5~10.0,降低了系统氯离子积累;提升淋洗合格液中铀质量峰值浓度,并将其维持在80~130 g/L;自动控制酸化过程的盐酸添加量,精准控制pH在4.5~4.6,进一步降低合格液中的碳铀比;调整淋洗合格液的流量,保持淋洗合格液平均铀质量浓度为30~70 g/L,降低合格液铀质量浓度对产品质量的影响;控制浆体沉淀时间,提升浆体压滤效果。优化生产参数后,产品水分降低了8.50%,铀含量提升了2.88%,产品质量整体提升。

成品油输送管道泄漏位置定位及改进方法研究

针对成品油输送管道泄漏位置定位问题,首先对负压波监测技术进行分析,在此基础上,引入流量法和激光监测法,对成品油输送管道泄漏位置定位改进方法进行研究,为及时发现成品油输送管道泄漏问题并对位置进行定位奠定基础。

利用变分模态分解对石油炼化压力管道泄漏检测方法改进

本文针对现有检测方法在对石油炼化压力管道泄漏检测时,存在检测定位泄漏位置与实际相差较大的问题,引入改进变分模态分解,开展石油炼化压力管道泄漏检测方法研究。对石油炼化压力管道单端泄漏位置进行定位,结合改进变分模态分解,对检测信号进行增强处理,最后实现信号能量瞬时变化追踪与泄漏检测。通过对比实验证明,新的检测方法可以实现对石油炼化压力管道泄漏的精准定位,且稳定性高。

H_(2)S分压对SA387M Gr.11CL2(H)炼化管道用钢腐蚀行为的影响

为了探究H_(2)S分压对SA387M Gr.11CL2(H)炼化管道用钢腐蚀行为的影响,采用高压釜进行试验,通过SEM,EDS,XRD和EPMA分析了SA387M Gr.11CL2(H)钢腐蚀产物的形貌、成分和物相。结果表明,随着H_(2)S分压(PH_(2)S)的增加,SA387M Gr.11CL2(H)钢的腐蚀减薄量增大。PH_(2)S≤0.5 MPa时,以全面腐蚀为主;PH_(2)S=1.0 MPa时,钢发生全面腐蚀伴随局部腐蚀,应力促进了局部腐蚀。SA387M Gr.11CL2(H)钢耐硫化物应力腐蚀性能良好。PH_(2)S≤0.5 MPa时,腐蚀产物膜中Cr的化合物和具有保护性的硫铁化合物发挥协同作用,有效阻止介质中Cl-的侵入;PH_(2)S=1.0 MPa时,腐蚀产物膜中Cr的化合物含量少,生成的硫铁化合物不具有保护性。H_(2)S分压影响了腐蚀产物膜的生成;Cr的化合物和硫铁化合物的组成和结构的变化,是导致SA387M Gr.11CL2(H)钢发生全面腐蚀和局部腐蚀的主要原因。

破碎和均细化处理方式对胡萝卜汁中类胡萝卜素释放的影响

为研究不同破碎和均细化处理对胡萝卜汁中类胡萝卜素释放途径的影响,采用打浆﹑胶体磨和高压均质3种破碎和均细化方式处理胡萝卜汁。应用分光光度法对处理后不同植物组织(大细胞聚集体﹑小细胞聚集体和有色体)中类胡萝卜素含量,游离类胡萝卜素含量,总类胡萝卜素含量,油脂可萃取类胡萝卜素含量进行测定。应用激光共聚焦扫描显微镜观察不同处理后类胡萝卜素的分布情况。利用高效液相色谱法对油脂可萃取类胡萝卜素单体含量进行测定。通过显著性分析确定不同均细化处理对以上3种植物组织中类胡萝卜素含量﹑游离类胡萝卜素含量﹑总类胡萝卜素释放率和油脂可萃取总类胡萝卜素含量及单体含量的影响。结果表明破碎和均细化处理后,大细胞聚集体中类胡萝卜素所占比例减小(从36.18%减小至15.28%),小细胞聚集体(从11.11%增加至15.73%)和有色体部分(8.36%增加至30.56%)中类胡萝卜素所占比例增大,类胡萝卜素释放在对其释放阻碍程度低的组织部分中。经过均细化处理后,激光共聚焦显微镜下可见的类胡萝卜素颗粒减少,处理越均细,可见的类胡萝卜素颗粒越少。对胡萝卜汁处理越均细,胡萝卜汁中类胡萝卜素释放率越高,其中胶体磨和高压均质联合处理胡萝卜汁后类胡萝卜素的释放率为50.91%。对胡萝卜汁处理越均细,胡萝卜汁中油脂可萃取总类胡萝卜素﹑β-胡萝卜素和α-胡萝卜素含量越少。研究结果对后续分析如何提高胡萝卜汁中类胡萝卜素生物利用率提供依据。

Al3Ti1B1RE细化剂对罐用铝材的细化效果及稀土的作用

采用XRD,OM,SEM,EDAX等探讨了一种新型Al3Ti1B1RE中间合金细化剂对罐用铝材的细化效果及RE的作用。结果表明,该细化剂对罐用铝材的细化效果优于进口和国产Al5Ti1B,且具有长效性,达6h后仍未见明显衰退,明显提高了该材料的强度和塑性;其细化效果及稳定性好的主要原因是:RE可降低铝液的表面能,增加铝液对细化核心(如TiAl3,TiB2)的润湿性,既充分发挥了异质形核作用,又防止了TiB2聚集沉淀倾向;RE也极易在结晶前沿富集造成成分过冷,阻碍了α Al晶粒生长,并促进其在细化核心上形核;此外RE还兼有一定的净化、细化和变质作用,尤其是净化作用提高了该细化剂的冶金质量。