液液喷射混合器最佳引射角度的CFD模拟

利用CFD模拟方法,研究了液液喷射混合器中引射流体进料角度的影响行为和优化选择问题。选择7种不同引射角度为考察对象,考察了喷射器内部流体的流动特性与掺混效果。结果表明:不恰当的引射角度将导致引射流体在喷嘴外围环隙的速度和流量分配不均,进而导致流场偏移;随着引射角度的增加,压力降、喷射系数、混合段流体速度和湍流耗散率呈现出先增大后减小的变化趋势;不同引射角度下流体达到混合完全所需要的距离相同,但是质量分数存在差别。综合分析,在7种引射角中,引射流体的最佳引射角度为60°,此条件下喷射器内混合段流体速度大,喷射系数高,混合效果好,同时对管壁的冲击力小。     

液-液喷射器不同进料方式下混合过程的CFD模拟

利用计算流体力学(CFD)软件CFX5对液-液喷射器混合段物料的混合性能进行了模拟,确定了工作流体和引射流体都平行于混合管轴线进料时物料完全混合所需的混合管长度,并分析了三种不同进料方式:(1)工作流体和引射流体都与混合段轴线平行进料;(2)工作流体与混合段轴线平行进料,引射流体与轴线成30°进料;(3)引射流体与混合段轴线平行进料,工作流体与轴线成30°,对混合管内混合过程的影响,结果表明,工作流体和引射流体都与混合段轴线平行进料时混合效果最好。     

喷射反应器内液-液快速反应的数值模拟

对于复杂快速反应,反应物之间能否快速均匀地混合是影响反应转化率、选择性和收率的重要因素,而喷射器作为一种高效混合设备,以它固有的优越性,越来越受重视。本文以酸碱快速中和反应为例,利用CFX5软件,采用k-s模型．将主动流体与引射流体的速度,在不同比值下对反应的影响作了模拟,结果表明,流速比决定反应的速度,流速比越大则反应越快,消耗的动力也越多,因此对于实际的喷射反应器,它必然有一个最优的速度比值。另外,本文还对流速比确定,不同反应物浓度比对反应的影响进行了模拟,结果表明浓度比对反应的影响很小,可以忽略。     

高Schmidt数下喷射器内湍流混合的多尺度模拟放大研究

本文从微观与宏观两个方面考察了喷射器的混合性能.利用CFD模拟软件Fluent 6.2求解了混合模型方程、流体流动方程及k-ε湍流模型方程,对不同结构、不同工况下的喷射器进行了考察,结果表明:1)在喷射器结构一定的情况下,喷嘴速度和引射流体速度比越大混合效果越好;2)在喷射器结构、喷嘴速度与引射流体速度比为定值的情况下,其绝对速度越小混合效果越好;3)在喷射器速度为定值的情况下,混合段直径与喷嘴直径比越小混合效果越好,二者之间存在着线性关系;4)在喷射器速度、混合段直径与喷嘴直径比为定值的情况下,其绝对直径越小混合效果越好,且二者之间存在着线性关系;5)在多数情况下,微观混合速度要慢于宏观混合,微观混合才是喷射器内混合过程的控制步骤.     

喷射反应器内液-液湍流微观混合的研究

通过定义局部分离度,来定量表征喷射器内液-液湍流微观混合规律。其定义式为:(实验所得H~+浓度-模拟所得H~+浓度)/模拟所得H~+浓度。选用酸碱反应体系,利用PLIF技术得到沿喷射器轴线的H~+浓度;采用Fluent软件,利用Standard k-ε模型,模拟获得相同操作条件下的H~+浓度变化趋势。得到不同操作条件下,分离度沿喷射器轴线的变化,结果表明:(1)引流速度不变,喷嘴速度越大,两流体越容易达到微观尺度的均匀混合;(2)喷嘴速度不变,引流速度越大,两流体反而不容易达到微观尺度上的均匀混合;(3)速度比一定的情况下,喷嘴速度越大,越有利于流体的微观混合。     

乙酸催化加氢制乙醇反应动力学研究

我国的能源结构是"富煤、贫油、少气",以煤基乙酸为原料制备燃料乙醇是适宜我国国情的工艺路线,燃料乙醇的研究越来越受到人们的关注。本文研究了贵金属催化剂上乙酸加氢还原制乙醇的反应。在反应温度（160～240）℃、反应压力（3～7）MPa、乙酸液相体积空速（0.3～0.7）h^-1、氢气与乙酸摩尔比5～22的条件下,在等温积分反应器中研究了乙酸加氢制乙醇的反应动力学,并考察了操作条件对乙酸转化率及乙醇选择性的影响。结果表明:随温度升高乙酸转化率和乙醇选择性均明显增加,在240℃时,乙酸转化率接近平衡转化率;增加反应压力,乙酸转化率及乙醇选择性随之增加;提高乙酸液相体积空速,乙酸转化率降低,乙醇选择性呈增加趋势。根据实验数据,应用参数估值方法,得到Langmuir-Hinshelwood型动力学模型中的参数,残差分析及统计检验表明,该动力学模型是适宜的。     

超音速氧气射流对电弧炉熔池作用

论文利用Fluent 6.3,通过对某钢厂150t 电弧炉冶炼过程中不同供氧流量 下超音速氧气射流冲击熔池流场进行三维三相流数值模拟,研究电弧炉熔池在炉壁侧吹氧枪 作用下的流场分布及其变化情况,探讨超音速氧气射流对电弧炉熔池的作用。研究表明氧气 射流冲击熔池引发钢液渣液流动波动,流动速度（冲击动能）以波的形式由冲击点向熔池中 心传递。熔池的速度场分布呈现“周围高、中心低,表层高、底部低”的趋势;由于射流的作 用,熔池内部生成涡流。涡流中心是钢液循环的中心,对钢液循环流动速度场有重要作用。 随着供氧流量的增加,涡流中心越远离氧枪,且在熔池中越深;氧气射流在熔池表面生成的 冲击凹坑在渣层中间横截面的冲击面积S(m2)和供氧流量QO2(m3/h)成线性关系,可表示为： 2 0.0004 * 0.0932 。     

上喷式喷射器内气液两相流的流体力学特征

喷射器作为气液混合装置,比传统接触混合器具有更高的混合强度和传质系数.计算流体力学(computational fluid dy-namics,CFD)模拟作为研究气液混合流的方法,有助于理解喷射器的流体力学和混合特征.它能提供详细的信息来量化操作条件对喷射器性能的影响.本文利用CFD模拟了上喷式喷射器内的气液两相流的流体力学特征.结果表明在较高的混合段长径比下,混合段入口处的压力较低.但是存在一个最大的压力降,此时混合段长径比约为4.0.在相同的喷嘴速度下,混合段入口处压力降最低,气体卷吸量最大.模拟中混合管与喷嘴面积比范围为1～16.无论是保持喷嘴直径不变还是混合管直径不变,混合段入口处的压力都随着D2M/D2N的增加而增加.但是对应的最大气体卷吸率发生在面积比为4.0.当喷射器的结构参数不变,混合段入口处的压力降和气体卷吸率随着喷嘴速度的增加而增大.     

粘性圆柱射流撞击理论研究

撞击式喷嘴在液体火箭发动机中得到广泛的应用,目前对射流撞击形成液膜的理论分析还仅限于无粘或低粘性流体。从流体力学基本方程入手,引入粘性力和撞击过程中的能量损失对现有模型进行修正,得到了粘性圆柱射流撞击形成液膜的理论模型,并对撞击角、射流速度及粘性系数等参数对液膜形状、厚度及速度的影响进行了分析。配制了不同粘度的甘油水溶液进行射流撞击实验,以验证理论模型的正确性。     

甲醇在加压条件下脱水生成二甲醚的动力学研究

在压力3.0 MPa～5.0 MPa、反应温度260℃-380℃、液空速(2.5～8.0)ml/(g·h)条件下,在等温积分反应器内,采用0.154 mm～0.198 mm的CM-3催化剂,考察操作条件对甲醇转化率的影响,测定甲醇气相脱水生成二甲醚的反应动力学实验数据.实验结果表明,随着压力的增加,甲醇转化率下降;加压条件下,温度提高甲醇转化率提高,在380℃左右接近平衡;甲醇转化率随着空速的增加而降低.以Langmiur均匀吸附双曲型动力学方程式建立以各组分逸度表示的本征动力学模型,根据实验数据用参数估值方法获得动力学模型中的参数.残差分析和统计检验表明,动力学模型是适宜的.     

Simulation of the effect of geometric parameters on tangentially injected swirling pipe airflow

A realizable k–ε turbulence model is employed to study compressible tangentially injected swirling flow in the nozzle of air–jet spinning. The effects of the nozzle geometric parameters (the injection angle, the diameter, number and position of the injector, nozzle length and chamber diameter) on both the flow and yarn properties are investigated. The simulation results show that some factors, such as velocity distribution, reverse flow in the upstream of the injector and vortex breakdown in the downstream caused by the nozzle geometric variation, are significantly related to fluid flow, and consequently to yarn properties. With increase in the injection angle or injector diameter or injector number, in the downstream of the injector, velocities will increase somewhat, and the locations of vortex breakdown move downward. As injector number increase with the total injection area being kept constant, the strength of vortex breakdown in the downstream of the injector will slightly increase. A larger reverse flow will be not helpful to draw the fibers into nozzle, as the injector position is closer to the nozzle inlet. The flow is more turbulent for a larger chamber diameter.     

Simulation of air flow in the typical boiler windbox segments

Simulation of turbulent air flow distribution in CFBC furnace, wherein primary air is entrained through inlet duct system called windbox, is attempted through state of art CAD/CFD softwares. Establishment of flow in windbox channel, distributed plate nozzle and combustor is complicated, due to sharp turns and presence of several solid boundaries makes the fluid flow highly turbulent. Hence, the simulation process is aimed in different parts to understand the flow behavior in each of the component associated with windbox. Towards this, the present paper develops the basic understanding for airflow distribution in windbox channel, wherein air exit is considered only through 6×3 array of distributed plate nozzle bottom faces. This analysis also highlights that recirculation flow, at several locations of windbox channel/distributed plate nozzle, which aids to generate high pressures zones and severe turbulent fluctuations. These effects in turn leads to unequal air-flow at exit, which are unable to carry the incoming crashed coal particles and lime stones to furnace for efficient combustion.     

Evaluation of flow maldistribution in air-cooled heat exchangers

Investigation of the evaluation of flow maldistribution in air-cooled heat exchangers is presented. The flow field in the inlet and return headers was obtained through the numerical solution of the governing partial differential equations including the conservation equations of mass and momentum in addition to the equations of the turbulence model. The effects of the number of nozzles, nozzle location, nozzle geometry, nozzle diameter, inlet flow velocity and the incorporation of a second header on the flow maldistribution inside the tubes of an air-cooled heat exchanger were investigated using a 3-D computational method. The results are presented in terms of the standard deviations of the mass flow rate and static pressure in addition to the distributions in the static pressure inside the inlet header of the air-cooled heat exchanger. The results indicate that reducing the nozzle diameter results in an increase in the flow maldistribution. 25% increase is obtained in the standard deviation as a result of decreasing the diameter by 25%. Increasing the number of nozzles has a significant influence on the flow maldistribution. A reduction of 62.5% in the standard deviation of the mass flow rate inside the tubes is achieved by increasing the number of nozzles from 2 to 4. The results indicate that incorporating a second header results in a significant reduction in the flow maldistribution. Fifty percent decrease in the standard deviation is achieved as a result of incorporation of a second header of 7 holes. The results indicate that the mass flow rate and the static pressure distributions become uniform at the inlet of the second pass.     

Numerical investigation of air suction through the louvers of a funnel due to high velocity air jet

The present investigation predicts the suction flow rate from the atmosphere through the louvers of a funnel (used in naval and merchant ships) when the high velocity exhaust comes out from a nozzle or a set of nozzles placed inside the funnel. Conservation equations of mass and momentum have been solved for the funnel with a surrounding computational domain so that the suction can take place at the louvers entry. The resulting equations have been solved numerically using finite volume technique in an unstructured grid employing eddy viscosity based two equation k-ε turbulence model. It has been found from the computation that the air suction rate into the funnel increases with the increase in louvers opening area, nozzle flow rate and height of the funnel. There exists optimum protrusion of the nozzle into the funnel for which maximum suction of air can be achieved with a prescribed nozzle flow rate and all other parameters of the funnel remaining fixed. Similarly there also exists optimum funnel diameter where the suction rate of air becomes the highest with all other parameters remaining fixed. There also exists optimum louver opening area on the funnel where the suction rate becomes the maximum as a function of the funnel diameter. The inclination of the funnel with respect to the vertical has no effect on mass ingress of air into it. An optimum nozzle diameter could be decided for a particular funnel diameter by considering the funnel suction rate and the back pressure developed by the nozzle per meter length of the pipe containing the nozzle (intersection of the two curves gives the optimum point of operation).     

适用于低流速的恒温式液体流量传感器

给出一种能在低流速范围有较高灵敏度的液体流量传感器。在测量水的情形下,当流速为1cm/s时传感器的输出可达30mV,该灵敏度比类似条件下氮气敏感的灵敏度高约一个数量级。该传感器利用维持芯片温度恒定所需的加热功率的变化作为流速的量度。它由标准的铝栅CMOS工艺制成。     

Studying on water nanojet ejection and the wetting phenomena on the nozzle surface

In this research, molecular dynamics simulations of water nanojet ejection out of nozzle holes with various sizes under various pressing forces are performed. The water molecules are ejected out the nozzle by a back plate on which a constant force is applied. The results of MD simulations of water ejection show that after one ejection, about 1.3?C2.5% of total molecules accumulate on the nozzle plate surface. These molecules affect the ejection of water jet thereafter. The cause of the accumulation of wetting water is investigated by analyzing the trajectories of these molecules. It is found that in the firing chamber near the nozzle plate wall, the arrangement of water molecules is aligned by the surface topology of the metal wall. Water molecules are packed into filamentous structure and these lines stack up at equal distances to each other. Water molecules drift along these lines, the trajectories of these molecules are sinuous, the velocity directions of them are random; molecules drift along the parallel lines until they reach a region of low pressure beneath the nozzle opening. These molecules eject out through the edge of the nozzle, they fall back on to the nozzle surface and eventually deposit on the nozzle surface due to low ejection velocity.     

The flow structure inside a microfabricated inkjet printhead

A micrometer resolution particle image velocimetry system has been adapted to measure instantaneous velocity fields in an inkjet printhead. The technique uses 700-nm-diameter fluorescent flow tracing particles, a pulsed Nd:YAG laser, an epi-fluorescent microscope, and a cooled interline transfer charge-coupled device camera to record images of flow tracing particles at two known instances in time. Instantaneous velocity vector fields are obtained with spatial resolutions of 5-10 μm and temporal resolutions of 2-5 μs. The relationship between instantaneous velocity fields is compared to instantaneous shapes of the meniscus. The flow in the nozzle is highly unsteady and characterized by a maximum velocity of 8 ms^-1, Reynolds numbers of Re=500, and accelerations of up to 70 000 times gravity (i.e., 70 000 g). Since the flow field is periodic for each ejection cycle, the instantaneous measurements can be phased averaged to determine the evolution of the average flow field. The ejection cycle period is 500 μs, and consists of four primary phases: infusion, inversion, ejection, and relaxation. During infusion, the actuator plate is deflected downward creating a low pressure that draws fluid into the inkjet cavity through the orifice and pulls the meniscus into the cavity through the nozzle. The meniscus grows, begins to decrease in size, and then deforms in shape, becoming inverted for approximately 6 μs. The meniscus exits the cavity through the nozzle during droplet ejection. During relaxation, the flow undergoes viscously-damped oscillations, and reaches equilibrium before the next ejection cycle begins     

警用脉冲防暴水炮管外动力过程数值模拟

为研究脉冲防暴水炮发射后在管外的动力过程,在Open FOAM软件上利用LES和VOF相耦合的方法对脉冲防暴水炮气液两相流流动过程作数值模拟。对水炮发射过程及其在距端口1.5m范围内的压力分布和速度分布做了分析。用SAMPLE软件对流场数据进行了采样,得到了用其它手段难以获得的数据。模拟表明,液柱形状急剧变化,首先形成蘑菇形,接着被压缩成半球形,在球形内部压力的作用下,半球形液弹被压缩成弧形。压力的作用距离集中在距端口300mm范围内,并很快降到了0.4MPa以下,其间因为压力有一个二次突然释放的过程,造成了二次喷射现象。速度是一个急剧先增加后减小的过程。所采用的圆柱式喷嘴使压力和速度下降太快,不利于提高水炮射程,需要改用其它类型的喷嘴。     

旋转固体火箭发动机统一流场计算

为了进一步研究旋转对固体火箭发动机工作的影响,采用RSM湍流模型对内孔燃烧、内孔与端面同时燃烧管状装药旋转固体火箭发动机统一流场进行了仿真。采用UDF编程给出质量入口边界,获得了旋转条件下发动机内流场结构参数特点,并给予理论说明。计算结果表明,内孔燃烧装药发动机切向速度流场类似于典型的Rankine涡,端面和内孔同时燃烧装药发动机切向速度流场呈现出Rankine涡和由端面燃烧引起的强迫涡的复杂组合涡;在发动机前封头和喷管喉部涡核切向速度峰值非常大,使燃烧室前封头和喷管喉部工作环境显著恶化;旋转使发动机燃烧室压力沿径向逐渐增大,强迫涡附近的压力梯度远大于推进剂表面的压力梯度。     

The decomposition method for Cauchy advection-diffusion problems

In this paper, the solution of Cauchy problems for the advection-diffusion equation is obtained using the decomposition method. In the case when the flow velocity is constant, an analytical solution can be derived, whilst for variable flow velocity, symbolic numerical computations need to be performed.