改进型撞击流反应器的颗粒混合特性

撞击流技术是现代社会强化过程的一种手段,具有巨大的发展潜力和应用前景。然而,在传统撞击流反应器中,颗粒混合效果不佳,导致相关反应进行不充分。为此一种入口速度动态变化的撞击流反应器应运而生,反应器的流场同样分为入口区、撞击区、出口区和漩涡区,但撞击面在几何中心处波动,从而使颗粒的混合区域扩展到整个反应器,并采用流体计算动力学对该改进型的撞击流反应器进行数值模拟。在保证平均流量相同的情况下,采用三角直线型的流速进入撞击流反应器,并与传统撞击流反应器进行分析对比。分析结果表明,颗粒的活动范围得到了有效地加强,与传统撞击流反应器有明显的优势,可以实现颗粒理想混合和相关反应充分进行。     

撞击流反应器流场稳定性研究

采用数值模拟的方法研究对置喷嘴撞击流,分析了撞击流流场结构,创建了7种不同管径比的几何模型,分别为1/3、1/5、1/7、1/10、1/12、1/15、1/20,同时也考察了气流雷诺数对稳态和非稳态撞击流稳定性的影响。研究结果表明,撞击流的稳定性与撞击流的几何模型及入口雷诺数有关,撞击流流场可分为入口区,撞击区,出口区及漩涡区。对于非稳态工况下,在入口气流雷诺数一定情况下,管径比大于1/10的模型都能形成稳定的撞击流,管径比小于1/10的模型中撞击流形成一段时间后都会失效。当管径比一定时,随着雷诺数的增大,撞击流持续时间在减小,变化形式依据不同管径比而不同。     

斜流叶轮顶端间隙流动特性的研究

使用单倾斜热线及其测试系统，在不同顶端间隙条件下，对翼形和圆弧形料流叶轮的间隙流动特性进行了实验研究，着重考察了顶端泄漏流动对斜流叶轮出口流场及其二次流对叶轮性能的影响。     

撞击流反应器流场速度时间序列的结构复杂性研究

结合谱熵和小波熵算法,从整体及各个尺度上,对撞击流反应器(Impinging stream mixer,ISM)流场速度时间序列进行结构复杂性分析。谱熵算法描述时间序列信号的谱的结构情况,反映序列频率谱的集中程度,从而体现ISM流场速度信号的总体的平均功率的分布情况;小波熵算法充分利用小波变换的多分辨、多尺度特性,使信号在结构上的复杂性得以清晰体现。研究表明,尺度a4上的小波熵分布与系统的结构复杂性的分布类似,说明该系统的信号的主要特征集中在低频细节成分a4尺度上。不同尺度下的小波熵表征信号在各个频段的变化趋势,体现信号在时域和频域上的信息。该系统的轴向流体结构复杂性大小沿轴线没有特定的变化规律,但径向流体结构复杂性大小呈对称分布,且在轴心取得最大值。     

油气润滑气液两相环状流流动特性分析

建立油气润滑气液两相环状流的数学模型,通过Fluent仿真,研究水平管内环状流的形成机制以及油气流速对其影响趋势。结果表明:气液两相流型随气相速度的变化,从分层流向环状流和雾状流转变,其中分层流向环状流的转变是附壁效应和气相涡旋流动的结果,环状流向雾状流的转变是气相撕裂油相形成细小油滴,并均匀混合的结果;在一定范围内最短进口长度和气速成正比关系。     

流化床撞击流气流粉碎机拉瓦尔喷管研究

流化床撞击流气流粉碎是对矿物进行超细粉碎的重要方法，喷管是其最关键部件之一。根据流体力学理论对流化床气流粉碎喷管进行了研究，提出了轴对称撞击流速度势函数表达式和喷管直径变化方程，并根据相关理论对超声速拉瓦尔喷管进行了设计和制造。实验证明，采用该喷管对煤进行超细粉碎，在喷管人口压力为0．7MPa～1．0MPa、转速分级轮转速〉2400r／min条件下，粉碎产品中以粒径小于2μm的颗粒为主，对煤具有良好的超细粉碎效果。     

不同阀芯结构节流阀流阻特性研究

基于标准k-ε湍流模型对四组不同阀芯结构(平底、小弧、大弧、波浪形)调节阀流阻性能进行研究,分析流场内速度流线、压力云图,得到流动规律及阀前后压力损失,流阻系数ξ。研究表明:随着阀芯开度增加,阀内流阻系数逐渐减小。10%开度时平底阀芯结构调节阀内流阻系数最大,大弧形与波浪形阀芯结构调节阀的流阻系数最小,对比发现大弧形与波浪形阀芯结构调节阀的截阻性能较平底阀芯调节阀的流阻系数值减小9.71%;全开度下大弧、小弧阀芯以及波浪形阀芯调节阀内部流阻系数相近,平底阀芯全开度下流阻系数相较于其他三组减小了14.69%。表明该工况下,阀芯处于全开度时,平底阀芯截阻性能具有一定的优势,因此,调节阀在小开度工况下工作时可选用大弧阀芯与波浪形阀芯结构。     

超高压超临界撞击流实验平台

提出超高压超临界撞击流概念,应用其开发设计超高压超临界撞击流工作平台,应用缓冲罐,及连续工作原理设计了超高压连续进料装置,解决了超高压状态下的连续进料问题,分析了其结构和工作原理,将其应用于超细粉碎,乳化和萃取过程,显示其独特的优越性,在灵芝孢子的破壁实验中效果令人满意.     

冰箱毛细管内流动特性的研究

利用毛细管四段流阻模型,用数值模拟的方法详细讨论了冰箱毛细管在不同工况下的性能,研究了冷凝温度、蒸发温度及过冷度对毛细客流量的影响,并首次对冷凝不充分的含汽制冷液进入毛细管的流动特性进行了讨论,以及做了验证实验。研究结果和编制的软件对毛细管的设计和应用将有一定的借鉴意义。     

流化床撞击流气流粉碎机拉瓦尔喷管研究

流化床撞击流气流粉碎是对矿物进行超细粉碎的重要方法,喷管是其最关键部件之一.根据流体力学理论对流化床气流粉碎喷管进行了研究,提出了轴对称撞击流速度势函数表达式和喷管直径变化方程,并根据相关理论对超声速拉瓦尔喷管进行了设计和制造.实验证明,采用该喷管对煤进行超细粉碎,在喷管入口压力为0.7 Mpa～1.0 Mpa、转速分级轮转速＞2400r/min条件下,粉碎产品中以粒径小于2 μm的颗粒为主,对煤具有良好的超细粉碎效果.     

An experimental study on the flow and heat transfer characteristics of an impinging jet

The flow and heat transfer characteristics of an impinging jet is investigated in two major stages. The first stage is about the investigation of the three dimensional mean flow and the turbulent flow quantities in free jet, stagnation and wall jet region. After a complete documentation of the flow field, the convective heat transfer coefficient distributions on the impingement plate are presented, during the second stage of the study. Heat transfer experiments using the new hue-capturing technique result in high resolution wall heating rate distributions. The technique is fully automated using a true color image processing system. The present heat transfer results are discussed in detail in terms of the flow characteristics. The measurements from the new method are compared with conventional heat flux sensors located on the same model. These heat transfer distributions are also compared with other studies available from the literature. The new non-intrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with good accuracy.     

Large eddy simulation of flow characteristics in an unconfined slot impinging jet with various nozzle-to-plate distances

To study the detailed flow structure of the unconfined plane impinging jet, a 3-dimensional flow analysis is carried out focused on the flow mechanism with the non-dimensional distance, L/d, as flow parameter by using the LES turbulent technique. The symbols d and L represent the nozzle width and the nozzle-to-plate distance, respectively. Then, the flow structures along both the stream-wise and spanwise direction are investigated. For these purposes, the plane impinging jet with Reynolds number of 11,000 is analyzed. The nozzle width was fixed at 1.5mm, but the nozzle-to-plate distance was varied between 4mm and 24mm. As a result, the plane impinging jet shows different flow patterns with L/d. In conclusion, the plane impinging jet is classified into three types with the non-dimensional variable, L/d. L/d≤4: Stable impinging jet, 4<L/d<11: periodically-stable impinging jet and L/d≥11: Unstable impinging jet.     

An experimental study on turbulent characteristics of an impinging split-triplet injector

This paper presents turbulent characteristics of an impinging F-O-O-F type injector in which fuel and oxidizer impinge on each other to atomize under the different momentum ratio. Water was used as an inert simulant liquid instead of fuel and oxidizer. The droplet size and velocity in the impinging spray flow field were measured using a PDPA. The gradient of the spray half-width(b₂) along the long-axis direction declined throughout the entire spray flow field with increasing the momentum ratio from 1.19 to 6.48. However, the gradient of the half-width(b₁) along the short-axis direction decreased with increasing the momentum ratio. The turbulence intensity and turbulent kinetic energy were converged into the center of the initial region with increasing the momentum ratio. As the momentum ratio increased from MR=1.19 to MR=6. 48, the turbulent shear stress decreased. The results of this study can be used for the design of an impinging type injector for liquid rockets.     

Gasoline spray characteristics impinging onto the wall surface in suction air flow

This study investigates the spray characteristics before and after wall impingingment of gasoline spray in suction air flow. For this study, a rectangular model intake port was made of acrylic glass, and suction air was generated by using the forced air blower contrariwise. The injector for this study was a pintle-type port gasoline injector in which an air-assist adaptor is installed to supply assisted air. A PDPA system was employed to simultaneously measure the size and velocity of droplets near the wall. Measured droplets are divided into “pre-impinging droplets” with positive normal velocity and “post-impinging droplets” were negative normal velocity for the suction flow. The velocities, size distributions and Sauter mean diameter (SMD) of pre- and post-impinging droplets for varions injection angles and air-assists are comparatively analyzed.     

Turbulent flow and heat transfer characteristics of a two-dimensional oblique plate impinging jet

Turbulent flow and heat transfer characteristics of a two-dimensional oblique plate impinging jet (OPIJ) were experimentally investigated. The local heat transfer coefficients were measured using thermochromic liquid crystals. The jet mean velocity and turbulent intensity profiles were also measured along the plate. The jet Reynolds number (Re, based on the nozzle width) ranged from 10, 000 to 35,000, the nozzle-to-plate distance (H/B) from 2 to 16, and the oblique angle (α) from 60 to 90 degree. It has been found that the stagnation point shifted toward the minor flow region as the oblique angle decreased and the position of the stagnation point nearly coincided with that of the maximum turbulent intensity. It has also been observed that the local Nusselt numbers in the minor flow region were larger than those in the major flow region for the same distance along the plate mainly due to the higher levels in turbulent intensity caused by more active mixing of the jet flow.     

Effect of cross-flow velocity on flow and heat transfer characteristics of impinging jet with low jet-to-plate distance

An effect of cross-flow velocity on flow and heat transfer characteristics of impinging jet in the case of low jet-to-plate distance at H = 2D was experimentally and numerically investigated. In the experiments, the air jet from orifice impingement on the wall of wind tunnel while a cross-flow was simultaneously induced normal to the jet flow. The jet velocity was fixed while the cross-flow velocity was varied corresponding to velocity ratios (jet velocity/cross-flow velocity) VR = 3, 5 and 7. The temperature distribution on an impinged surface was visualized by using thermochromic liquid crystal sheet (TLCs), and Nusselt number distribution was evaluated by using image processing method. The flow pattern on impingement surface was visualized by using oil film technique. The numerical simulation was carried out for a better understanding of the jet flow in the cross-flow. The results show that Nusselt number peak shifts downstream and the Nusselt number peak increases with increasing cross-flow velocity.     

The effects of the compressibility of the subsonic flow on heat transfer characteristics in a microscale impinging slot jet

We experimentally investigated the effects of both the compressibility and nozzle width on the local heat transfer distribution of microscale unconfmed slot jets impinging on a uniformly heated flat plate. We made heat transfer measurements under the following experimental conditions; Reynolds numbers of Re = 4000~10000, Mach numbers of Ma = 0.13~0.68, nozzle-to-plate distances of H/B = 3~25, lateral distances of x/B = 0~25, and nozzle widths of B = 300~700 μm having a nozzle aspect ratio of y/B = 30. A thermal infrared imaging technique was used to measure the impingement plate temperature. The experimental results show that for all tested Re and H/B values at a nozzle width of B = 300 μm, the Nusselt number maximum occurred nearly at the stagnation point and then monotonically decreased along the downstream. However, at B = 500 and 700 μm, the maximum Nusselt number point shifted toward x/B ≈ 1.5~2.0. And the Nusselt number increased, as x/B increased, from the stagnation point to the shifted maximum point and monotonically decreased afterward. This shifted maximum point may be attributable to vortex rings promoting sudden flow acceleration and entrainment of surrounding air moving along the jet axis. For the same Reynolds number, the Nusselt number in the stagnation region increased as the nozzle width increased due to a momentum increase of the jet flow caused by the formation of vortices. And, the Nusselt numbers for the smallest nozzle width of B = 300 μm (or highest Mach number at a given Reynolds number) at all H/B and Reynolds numbers tested significantly deviated from those for B = 500 and 700 μm in the downstream region corresponding to x/B > 5, suggesting that the compressibility, when it is high, can affect the heat transfer in the downstream region.

     

超高压和撞击流相结合的新方法在乳化均质方面的应用

传统的乳化方法处理后的物料粒径难以达到亚微米甚至纳米级,不能满足制备更高性能产品的要求。采用超高压和撞击流相结合的新方法,具备了高剪切和高压的均质乳化的双重作用机理,使得高速射流对撞过程中可以产生三个对微粒破碎和分散起重要作用的因素,因此所产生的乳液滴粒直径小,分布窄,并且能耗较小。阐述了新方法的基本原理,对工艺流程进行了研究。实验结果经过三种方法验证均达到比较好的效果。