水力空化联合二氧化氯处理苯酚废水研究

以苯酚废水作为研究对象,采用水力空化技术处理,考察了入口压力、孔板开孔率、孔板排布方式对苯酚降解率的影响,并研究了水力空化联合二氧化氯对苯酚的降解率。研究表明,苯酚降解率随着入口压力的增大,呈现先增大后减小的趋势,存在最佳压力;孔板开孔率对苯酚的降解效果有较大的影响,且环状分布孔板比均匀分布孔板有更好的降解效果;水力空化比超声空化有更高的能量利用率。水力空化联合二氧化氯对苯酚的降解符合一级反应动力学规律,且降解率是2个单独处理工艺之和的1.4倍,并结合对降解机理的探究,表明两者对苯酚的降解存在协同效应。     

壅塞空化降解水中苯酚的实验研究

水力空化是一种很有潜力的水处理技术。利用苯酚溶液作为模拟污水,溶液pH=6.5,经过60 min处理,分别对比了壅塞空化器、振荡腔喷嘴和普通喷嘴对溶液中苯酚的去除效果。结果表明,使用壅塞空化器时,苯酚的去除率达41.59%,分别是振荡腔喷嘴和普通喷嘴的4.5倍和6.6倍。壅塞空化器较之另两种空化器在降解水中苯酚时具有独特的优越性,特别适合于水力空化处理难降解污水的领域。     

文丘里管与孔板组合降解苯酚废水研究

利用水力空化技术,处理模拟废水苯酚,以文丘里管与不同的孔板组合作为空化装置。研究运行时间、入口压力、孔口排布方式及空化数对苯酚降解率的影响,并对苯酚降解的中间产物进行紫外-可见吸收光谱分析,初步判断降解过程中形成的产物性质。研究结果表明,随着时间的延长,苯酚的降解率先增大后趋于稳定,60 min时达到最大降解率;存在最佳入口压力,为0.4 MPa;孔口排布方式对苯酚降解率有较大影响。紫外-可见吸收光谱分析表明,苯酚降解过程的产物可能为酮类或醛类、苯二酚以及脂肪酸类物质。     

水力空化强化臭氧降解水中苯酚影响因素研究

研究了在水力空化强化臭氧降解苯酚时臭氧通入量、多孔板的参数、多孔板的入口压力对苯酚降解的影响。研究表明:三者对苯酚的降解均有较大影响。增加臭氧通入量、提高入口压力都有利于苯酚的降解。研究水力空化强化臭氧氧化作用的动力学,结果表明,苯酚在单独水力空化、臭氧氧化以及它们的联合工艺下的降解均符合表观一级动力学;且在水力空化强化臭氧氧化的工艺中苯酚的去除率比在单独水力空化、臭氧氧化时有显著的提高,表明水力空化强化臭氧氧化的工艺中存在协同作用。     

超声波强化Fenton试剂法降解对硝基苯酚废水

通过超声波产生的空化效应,对Fenton试剂法降解对硝基苯酚(PNP)进行了强化。研究了声强、溶液初始pH、H_2O_2的浓度等因素对超声波强化Fenton试剂法(US/Fenton)降解对硝基苯酚的影响。结果表明,随着声强和H_2O_2浓度的增大,PNP的降解率增大;较低的pH有利于US/Fenton法降解对硝基苯酚。在充分利用超声空化产生的特殊反应环境的同时,提高了Fenton试剂对PNP的降解效果。     

超声波强化Fenton试剂法降解对硝基苯酚废水

通过超声波产生的空化效应,对Fenton试剂法降解对硝基苯酚(PNP)进行了强化。研究了声强、溶液初始pH、H_2O_2的浓度等因素对超声波强化Fenton试剂法(US/Fenton)降解对硝基苯酚的影响。结果表明,随着声强和H_2O_2浓度的增大,PNP的降解率增大;较低的pH有利于US/Fenton法降解对硝基苯酚。在充分利用超声空化产生的特殊反应环境的同时,提高了Fenton试剂对PNP的降解效果。     

基于水力空化技术的废水处理装置及设计

水力空化技术是一种新的水处理技术。本试验利用两种孔板水力空化装置对若丹明B降解进行了试验研究,试验结果表明：水力空化对若丹明B确实有降解作用。探讨和分析了两种孔板的空化数和进口压力等因素对其降解的影响作用,提出了水力空化降解与时间的规律和不同的孔板存在最佳的操作运行参数的观点。     

文丘里管空化器内空泡动力学特性的数值模拟

研究了文丘里管空化发生器内空泡的成长、溃灭特性,根据基本的R-P空泡运动方程,考虑了液体粘性、表面张力和可压缩性等因素的影响,运用四阶Runge-Kutta法对空泡径向非线性运动方程进行求解,得到空泡径向演变过程以及溃灭压力的变化趋势.讨论了初始汽泡半径、入口压力和文丘里管的喉径比等因素对空泡演变过程的影响.结果表明,流体的可压缩性对空泡溃灭的影响最大;空化发生器结构参数以及操作参数均对空泡运动特性产生影响,从而影响空化强度.所得结果对空化流场中空化泡演变规律的研究以及水力空化发生器的设计具有指导意义.     

空化设备的研究进展

空化是液体压力突然降低而产生空泡,空泡随液体压力恢复而溃灭的过程。主要概述应用超声空化,水力空化,涡流空化和突体空化而开发的9种空化设备,分别阐明这些设备的工作原理、空化效果以及优缺点,为进一步研究空化设备提供参考。     

人工淹没空化水射流喷嘴内部流场研究

为了克服淹没水射流应用范围窄,有效靶距范围小的缺点,设计了一种新型的人工淹没空化水射流喷嘴,利用Fluent对人工淹没空化水射流喷嘴内部流场进行了数值模拟。数值模拟结果表明:人工淹没空化水射流喷嘴可以有效的产生空化现象,空化主要在内喷嘴扩散段和外喷嘴出口段产生;喷嘴结构尺寸影响流场空化效果,对于所设计的喷嘴,外喷嘴出口段直径为10 mm,内喷嘴出口至外喷嘴收缩段的距离为6 mm时,流场内空化效果最好。     

Numerical simulation of cavitation in the conical-spray nozzle for diesel premixed charge compression ignition engines

The conical-spray injector is capable of achieving lean mixture with high homogeneity in the cylinder for diesel Premixed charge compression ignition (PCCI) engine with advanced injection timing. To better understand the cavitating flow inside the conical-spray injector, numerical simulations have been conducted by using a mixture multiphase model and a full cavitation model in this study. The results indicate that the cavitation evolution significantly affects the liquid sheet thickness and velocity at nozzle exit, which further change the spray angle and droplet Sauter mean diameter (SMD) dramatically. Based on the cavitation distribution inside the nozzle, the cavitating flow inside the conical-spray nozzle can be classified into four regimes with no cavitation, cavitation inception at inlet, developing cavitation at nozzle exit and super cavitation respectively. The extension of cavitation to nozzle exit in the super cavitation regime significantly improves the fuel atomization by increasing the injection velocity and decreasing the thickness of the liquid sheet. A cavitation map for the conical-spray injector has been developed by sweeping the ambient pressure and injection pressure simultaneously. It is found that the phenomenon of super cavitation only occurs in a narrow region where ambient pressure is very low. Therefore, the start of injection timing should be kept well before top dead center (TDC) to ensure the occurrence of super cavitation inside the nozzle in order to provide more homogeneous fuel/air mixture for diesel PCCI engines.     

Numerical investigation on relationship between injection pressure fluctuations and unsteady cavitation processes inside high-pressure diesel nozzle holes

The relationship between injection pressure fluctuations and unsteady cavitation processes inside the high-pressure diesel nozzle holes have been numerically analyzed by using a two-fluid approach. In order to improve prediction of nozzle hole cavitation content under high-pressure injection conditions, a new adjustment model of bubble number density has also been developed through the analysis of cavitation bubble dynamics and internal flow characteristics of nozzle hole. Model validation results verify that this model is applicable for a wide range of diesel injection pressures. Based on simulation results, it has been found that cavitation bubbles in recirculation zone and its wake flow show totally different responses to the variations of upstream pressure, and the evolution of cavitation content shows a close association with the time derivatives of upstream pressure.     

A study on flow through hydroentangling nozzles and their degradation

Hydroentangling is a technique for mechanically bonding loose filaments or fibers arranged in a web. The efficiency with which the web is entangled depends on the peculiar properties of laminar high-speed waterjets used. The characteristics of such waterjets strongly depend on the operating pressure and the nozzle inlet sharpness which influence the dynamics of fluid flow. In this study, we report on experiments and CFD simulations aimed at improving our knowledge of such two-phase flows. In particular, we simulate the formation and growth of the cavitation cloud inside a sharp-edge hydroentangling nozzle at pressures ranging from 10 to . Our experimental results run at the same pressures, confirm that nozzle cavitation will cause “hydraulic flip”. Once hydraulic flip occurs, atomizing waterjets will turn into constricted laminar waterjets with long intact lengths—a necessary condition for hydroentangling. It has been observed that the nozzle inlet deteriorates under high pressures. Our CFD simulations show a striking similarity between the contours of shear stress at the nozzle inlet and the nozzle wear pattern. These findings together with the SEM elemental analysis at the nozzle inlet reveal the potential for metal oxidation around the inlet, implicating stress-induced corrosion as a major contributor to the nozzle wear. Cavitation might also be one of the mechanisms responsible for the above-mentioned wear at the inlet edge. Additionally, our water-borne solid particle tracking, confirms SEM experimental results that particle deposition can potentially play a considerable role in the deterioration of the nozzle inlet shape.     

Influence of cavitation phenomenon on primary break-up and spray behavior at stationary conditions

In this paper, a special technique for visualizing the first 1.5 mm of the spray has been applied to examine the link between cavitation phenomenon inside the nozzle and spray behavior in the near-nozzle field. For this purpose, a Diesel axi-symmetric nozzle has been analyzed. Firstly, the nozzle has been geometrically and hydraulically characterized. Mass flow measurements at stationary conditions have allowed the detection of the pressure conditions for mass flow choking, usually related with cavitation inception in the literature. Nevertheless, with the objective to get a deeper knowledge of cavitation phenomenon, near-nozzle field visualization technique has been used to detect cavitation bubbles injected in a chamber pressurized with liquid fuel. Using backlight illumination, the differences in terms of density and refractive index have allowed the distinction between vapour and liquid fuel phases. From these visualization results, two important conclusions can be established: on the one hand, cavitation bubbles have been detected at the nozzle exit for pressure drop conditions at which mass flow was not choked yet. On the other hand, it could be seen that the jet formed by cavitation bubbles spread as pressure drop conditions became stronger. Finally, spray visualization in a nitrogen pressurized chamber has been developed at stationary conditions. In order to analyze cavitation influence on spray characteristics, pressure drop has been modified near the values at which cavitation bubbles have been detected out of the nozzle. Two different test strategies have been used for this purpose: fixing injection pressure, which implied a change in chamber density for each test point, or fixing chamber pressure. Both kinds of measurements revealed a noticeable increment of spray cone angle and spray contour irregularities related with the presence of cavitation bubbles at the orifice outlet. This fact can be assumed as an indicator of atomization improvement induced by the collapse of cavitation bubbles at the nozzle exit.     

重油燃烧器Y型喷嘴气液两相流动与雾化特性模拟

为改善重油雾化质量,针对沥青站重油燃烧器Y型喷嘴,运用CFD (Computational Fluid Dynamics)方法研究了喷嘴结构参数(混合室长度、入口直径比、入口夹角)与雾化参数(重油流量、空气入口压力、重油温度)对喷嘴气液两相流动与雾化特性的影响。结果表明,结构参数与雾化参数直接影响喷嘴内油膜厚度与气液两相速度差;不同参数下,喷嘴气耗率与液滴索泰尔平均直径的变化规律相反;综合考虑两个雾化性能指标,混合室的适宜长度为15~20 mm,入口夹角的合理范围为60°~75°,入口最佳直径比为1.0~1.1;为保证重油获得较好的雾化效果,空气入口压力应大于0.5 MPa,这为优化Y型雾化喷嘴的结构与运行参数提供了参考。     

Using spray momentum flux measurements to understand the influence of diesel nozzle geometry on spray characteristics

Nowadays Diesel nozzle geometry is a major issue in order to fulfil new emission regulations due to the influence on internal flow, cavitation phenomenon, spray characteristics and therefore atomization behavior, which are very important for engines performance and pollutant formation.The aim of this article is to study the effect of cavitation on Diesel spray behavior. For this purpose, two bi-orifices nozzle geometries, a cylindrical nozzle and a convergent one, are characterized by means of two fundamental spray parameters: mass flux and momentum flux. Five injection pressure values and five discharge pressure levels have been measured in order to change the cavitation regime inside the nozzle flow. It is known from the literature that cavitation brings about a mass flux choke, but there are few studies that investigate its effects on momentum and outlet velocity in real geometries. The key point of this study is the measurement of spray momentum in order to explain the effects of nozzle geometry on spray behavior.     

水力空化对水中微生物的灭活作用及特性

在以文丘里管为空化发生器的水力空化装置中,对含有大肠杆菌的水体进行灭菌处理。通过检测大肠杆菌的灭菌率,考察了水力空化对水中微生物的灭活效果。分析了水流空化数、文丘里管入口压力、空化作用时间、文丘里管结构特性等参数对灭菌效果的影响。结果表明,水力空化的能量效应对水中微生物能够产生灭活作用,实现对含菌污水的灭菌消毒处理。提高文丘里管入口压力、增加空化处理时间、优化空化器结构设计均有利于增强空化灭菌效果。     

Numerical Study on the Effect of Cavitation on Flow and Diesel Fuel Atomization Characteristics

Computational fluid dynamics (CFD) models based on the turbulent mixture multiphase model were applied to consider the effect of cavitation on the spray of diesel fuel. The effects of injection pressure and length‐to‐width (L/W) ratio on the velocity distribution, cavitation number, discharged coefficient, and nozzle exit velocity were investigated and the performance of the model was compared with the experimental data. The results indicate that the cavitation generated in the nozzle has a strong impact on the fuel injection and spray quality, whereas the L/W ratio is a highly effective parameter for cavitation behavior. In addition, by increasing the L/W ratio, the range of cavitation number, wall friction, and flow resistance increase but in the cavitation region the velocity profile in radial and axial directions, spray cone angle, nozzle exit velocity, and the discharged coefficient decrease.     

跨临界CO2快速膨胀过程中非平衡冷凝和闪蒸机理的数值研究

跨临界CO₂在高速膨胀时,压力和温度剧烈下降,会发生非平衡相变。其中在天然气超声速分离设备和超临界CO₂离心压缩机中CO₂会发生非平衡冷凝相变;在引射膨胀制冷系统中,跨临界CO₂在引射器主动喷嘴中发生非平衡闪蒸相变。为解决跨临界CO₂在膨胀过程中物性变化剧烈,非平衡相变模拟困难的问题,构建了新型非平衡相变CFD模型,以研究跨临界CO₂在超声速缩放喷嘴中的非平衡冷凝和非平衡闪蒸的相变过程和膨胀机理,模型耦合了温度驱动的蒸发-冷凝相变机制和压力驱动的空化-冷凝相变机制,并用文献中的试验结果验证了模型的准确性。研究结果表明,在冷凝相变过程中,由压力驱动的冷凝传质具有主要影响,压力驱动的冷凝传质主要存在于喷嘴喉部与内流区域,温度驱动的冷凝传质主要存在于喷嘴渐扩段壁面。冷凝传质速率随着进口压力的增加和进口温度的降低而增加,从而使冷凝的非平衡程度和喷嘴内的干度降低,喷嘴渐扩段内达到声速的位置也相应延后。在闪蒸相变过程中,由温度驱动的蒸发传质占据主导,蒸发相变主要发生在喷嘴喉部附近,空化相变主要发生在喷嘴渐扩段,两相CO₂在喷嘴的渐扩段达到声速。随着喷嘴进口压力的增加和进口温度的降低,闪蒸的非平衡程度增加,使喷嘴内的干度减小。本研究有助于厘清跨临界CO₂快速膨胀中的非平衡闪蒸和冷凝相变机理,并为跨临界CO₂膨胀设备的分析和优化设计提供参考。