【作者】 梁瑛娜；

【导师】 高殿荣；

【作者基本信息】 燕山大学 ， 机械电子工程， 2008， 硕士

【摘要】 搅拌设备在化学工业、生物工程、制药工程、材料加工及食品加工等领域有着广泛的应用。当所处理的介质对剪切敏感时,通常要求搅拌处于低雷诺数的层流状态。如何应对随之而来的混合效率降低、副产品生成量增加等现象,成为层流搅拌槽研究中亟待解决的问题。本文对双层直-斜组合桨搅拌槽内混合的形成机理、流动特性、影响因素及在工程实际上的应用作了理论分析、数值模拟和实验研究。(1)对搅拌槽内的流动特性进行介绍,提出一种非对称混合的构想,运用桨叶组合结构的变化及其在搅拌槽中布置的非对称性,来增加对搅拌槽中层流流体的搅动,提高混合效率。(2)选用CFD软件FLUENT6.1,采用多重参考系法(MRF)及Laminar模型分别对安装有不同桨型组合叶片、槽径为Φ200mm的有机玻璃槽内的非牛顿流体(甘油和水的混合物)的搅拌流场进行数值模拟。研究了双层直叶片、双层倾斜叶片及双层直-斜组合叶片的同心搅拌、偏心搅拌及上下层叶轮相对于转轴反向偏心搅拌三种不同情况下的流场特性,并进行了对比分析。结果表明,桨叶的形状、组合结构等因素都对流场的形态有很大影响。(3)采用持续片光源、示踪粒子定性描绘出两种组合桨在三种不同空间布置方式搅拌槽内的宏观流动场,与数值模拟结果对照,流场形态基本一致,说明数值模拟方法能很好地模拟出实际情况。斜叶片使其上、下两循环圈交界处的合成速度不水平,以下压斜桨为例,它可使交界处的合成速度向下倾斜、上循环圈强于下循环圈,且斜叶片越多,这种现象越明显。更多还原

【Abstract】 Stirred equipment are widely used in chemical engineering, biomedical engineering, pharmaceutical engineering, material processing and food processing. When the media in stirred tank is shear-stress-sensitive, mixing is often required in a laminar flow state with low Reynoles number. How to deal with the attendant phenomena such as the mixing efficiency falling and the by-products increasing, have been becoming the urgent problem in laminar stirred tank study.In the paper, the studies of theory analysis、numerical simulation and experiment were done to reveal the form mechanism、flow characteristic、influence factor and application in engineering of mixing in double straight-gradient impeller stirred tank.(1)Introduce the flow characteristic in stirred tank, bring forward an idea of dissymmetrical three-dimensional mixing, and use the variety of impeller configuration and the dissymmetrical disposal in stirred tank to enhance the agitation of laminar fluid in stirred tank and improve the mixing efficiency.(2)Using CFD software FLUENT6.1, adopting MRF and Laminar-model to simulate separately the agitation flow field of non-Newtonian fluid (a mixture of glycerin and water) in aΦ200mm plexiglass stirred tank with different organizational impellers. Study the flow characteristic of double straight impeller、double gradient impeller and double straight-gradient impeller centered mixing、eccentric mixing and reverse eccentric to axis mixing, compare and analyse the simulation result. The results show that the factors such as shape of the blades、organizational structure have a great influence on the form of fluid field.(3)Using the durative laser sheet and the tracer particles to describe qualitatively the macro fluid field in the stirred tank with two organizational impellers in three different layouts. The flow field is basically consistent with the numerical simulation result, that is to say the CFD method can have a good simulation of the true situation. The gradient blade make the synthesis speed at the junction of the two circles which above and below it is not level. Take the pressure impeller for example, it can make the synthesis speed at the junction declined and the above circle stronger than the below one. And the more gradient blades it has, the more obvious this phenomenon is.更多还原