平面撞击流反应器流动模式、混合机理及过程强化研究

发布时间：2018-03-12 10:11

本文选题：平面撞击流　切入点：反应器　出处：《华东理工大学》2015年博士论文　论文类型：学位论文

【摘要】：撞击流作为强化混合的重要手段,已在煤气化和纳米粒子制备等领域得到成功应用。掌握撞击流流动及混合机理,对撞击流反应器的开发、设计和运行至关重要。本文采用实验和数值模拟相结合的方法,系统研究了平面撞击流的偏转振荡特性以及平面撞击流反应器内流体的流动、混合机理及过程强化。具体内容归纳如下：1.采用粒子图像测速仪、高速摄像仪和流动可视化等实验手段和大涡模拟对自由平面撞击流的偏转振荡进行了研究,考察了射流雷诺数、喷嘴间距、边界受限程度和射流宽高比等因素对偏转振荡的影响,揭示了偏转振荡产生和维持的原因。结果表明,射流自身不稳定性、撞击区撞击不稳定性是引起偏转振荡的本质原因,而速度和压力的周期性变化和转换是维持偏转振荡的原因；偏转振荡周期主要由射流速度和喷嘴间距决定,还受射流宽高比与边界受限程度的影响；与雷诺时均模型相比,大涡模拟所得的结果与实验结果吻合较好。2.对不同雷诺数和几何结构的平面撞击流反应器内流动特性进行了研究,重点研究了文献中尚未报道过的半偏转振荡,考察了射流间距、射流宽高比、反应器腔室深度和顶部空间等结构参数对半偏转振荡的影响,揭示了半偏转振荡的产生机制。结果表明,平面撞击流反应器内存在分离流、吞噬流、撞击面摆动振荡、半偏转振荡等流动模式；半偏转振荡发生在进口平面以下,其无因次周期约为自由平面撞击流的一半,临界雷诺数随着无因次射流间距和射流高宽比的增大而减小；半偏转振荡由平面射流自身不稳定性引起,且靠速度和压力变化来维持,反应器腔室顶部正压抑制了射流向反应器顶部偏转。3.基于平面撞击流不稳定性,设计了新颖的撞击流激励振荡装置,考察了雷诺数、激励频率、激励振幅和结构参数等因素对振荡行为的影响,获得了平面撞击流及反应器的激励振荡规律。结果表明,异步声波激励能够引起撞击面发生与激励频率一致的水平振荡,振幅小于10%的声波激励对偏转振荡影响不显著,随着同步或异步激励振幅的增大,偏转振荡会转变为居中碰撞或水平振荡。声波激励作用下平面射流涡旋结构的变化是引起振荡模式转化的主要原因。平面撞击流反应器内流量激励能够引起撞击面的水平振荡,且振荡频率与激励频率一致,而撞击面与反应器壁面的相互作用是摆动振荡产生的主要原因。当撞击面振幅小于0.5倍射流间距时,撞击面摆动振荡幅度与激励振幅和射流速度成正比,而与激励频率成反比。4.利用激光诱导荧光技术对平面撞击流反应器内的流体混合及激励强化过程进行了研究,考察了流体黏度、雷诺数、反应器结构参数、激励条件等对平面撞击流反应器内流动形态和混合效果的影响。结果表明,平面撞击流反应器内处于分离流模式时,流体的混合效果较差,而转变为自持振荡模式时,流体的混合效果显著提升。在射流间距较大的平面撞击流反应器内,较低雷诺数下发生了半偏转振荡,达到了良好的混合效果；激励能够明显提高低雷诺数分离流模式下的流体混合效果。
[Abstract]:As an important means to strengthen the impact of mixed, has been successfully applied in the coal gasification and the preparation of other fields. Grasp the impinging stream flow and mixing mechanism, the development of impinging stream reactor, it is important to design and operation. This paper uses the combined method of experiment and numerical simulation, oscillation characteristics of deflection plane impinging stream system research the plane and impinging stream reactor fluid flow and mixing process, strengthening mechanism. Specific contents are summarized as follows: 1. using particle image velocimetry, high-speed camera and flow visualization experiment method and large eddy simulation of deflection oscillation free plane impinging stream is studied, investigated the jet Reynolds number, nozzle spacing. The influence factors of boundary limitation and jet aspect ratio of deflecting oscillation, reveals the deflection produces and maintains the oscillation. The results show that the jet instability itself The impact, the impact of instability is caused by the nature of the reasons deflecting oscillation, and the periodic change and conversion speed and pressure is the reason of maintaining deflection oscillations; deflection period of oscillation is mainly determined by the jet velocity and jet nozzle spacing, is also affected by the aspect ratio and boundary limitation; compared with the Reynolds averaged model, large eddy the simulation results agree well with the experimental results of.2. on different Reynolds number and geometric structure of plane impinging stream reactor flow characteristics were studied, focusing on the half deflection oscillation has not yet been reported, investigated the jet distance, jet width ratio, influence the reactor chamber depth and space structure parameters on the top deflecting oscillation, reveal the mechanism of oscillation half deflection. The results show that the plane fluidwere has separated flow, phagocytosis flow, impact surface of swing oscillation, half deflection vibration On the flow pattern; half deflection oscillations occur at the inlet plane, the dimensionless period is about half of the free plane impinging stream, the critical Reynolds number decreases with dimensionless jet spacing and jet height width ratio increases; half deflection plane jet oscillation by itself does not lead to stability, and the changes of velocity and pressure. Maintain the reactor chamber at the top of positive pressure inhibited the shooting to the top of the reactor deflection.3. plane impinging flow instability based on the design of a novel impinging stream excited oscillation device, effects of Reynolds number, excitation frequency, excitation amplitude and the effect of structure parameters on the oscillation behavior, the oscillation characteristic of plane impinging stream and the reactor. The results show that the asynchronous acoustic excitation can cause the impact surface occurrence and excitation frequency oscillation level consistent, less than 10% of the amplitude of the acoustic excitation affects the deflection of oscillation is not significant, With the increase of synchronous or asynchronous excitation amplitude, oscillation deflection will be transformed into the middle level of collision or oscillation. Variation of wave excitation planar jet vortex structure is mainly caused by oscillation mode transformation. The planar impact flow reactor can cause the impact surface of horizontal vibration excitation, and the oscillation frequency and excitation frequency, and the impact of interaction surface and the reactor wall is the main reason for the swing oscillation. When the impact surface amplitude is less than 0.5 times the jet distance, the impact surface of swing oscillation amplitude and excitation amplitude and velocity is proportional to the excitation frequency and inversely proportional to.4. using laser induced fluorescence technique was studied for planar fluid mixing and impinging stream the incentive in the reactor intensive process, the effects of fluid viscosity, Reynolds number, the structure of the reactor parameters, excitation conditions on plane fluidwere flow Influence of morphology and mixing effect. The results show that the plane fluidwere in separated flow mode, poor mixing effect of fluid, and transformed into a self sustained oscillation mode, the mixing effect of fluid significantly. In the larger pitch plane jet impinging stream reactor, low Reynolds number under half deflection oscillation, achieves good mixing effect; incentive can significantly improve the fluid mixing effect of low Reynolds number flow separation mode.

【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ052

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