共查询到19条相似文献,搜索用时 953 毫秒
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《轻工机械》2021,(4)
针对在设计发酵搅拌设备过程中往往依赖经验判断传质混合效果以及能耗等的现状,课题组利用CFD技术对设计的4种搅拌模型进行气液两相流非稳态数值模拟。模拟采用了多面体网格划分物理模型以及滑移网格模型法求解,探究了其速度场、气相体积分数和功率耗损情况。结果表明:相同工况下,不同搅拌组合的流场特性差异较大;上桨采用径向流桨的搅拌组合形成的混合流场整体速度分布更均匀,能为釜内物质提供更佳的混合和传递效果;同时上桨和底桨采用6半圆叶圆盘涡轮桨的搅拌组合C气液分散性能更好;功耗方面,搅拌组合A组合C组合B组合D。模拟结果及分析可为气液反应釜搅拌器的设计及优选提供重要的参考。 相似文献
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结晶罐搅拌流场及传热过程的数值模拟 总被引:2,自引:0,他引:2
利用CFD技术分别对使用2种不同结构搅拌器的结晶罐内部流场进行详细分析,得到了结晶罐内的流场分布情况,基于流场分析结果获得搅拌功率等性能参数。同时通过流动与传热的非定常数值模拟,得到了结晶罐内壁面传热系数分布和强制冷却时结晶罐内部温度分布随时间的变化趋势,绘出结晶液冷却时的温度变化曲线,以上结果均可为该结晶罐搅拌器及换热结构的设计提供工程参考。图8表2参8 相似文献
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《轻工机械》2016,(3)
针对目前斜叶桨餐厨垃圾厌氧发酵罐存在搅拌能耗高、流场混合效果差等问题设计了新型轴流式搅拌桨(axialflow impeller,AFI)。采用FLUENT软件对斜叶桨和AFI桨发酵罐内流场进行数值模拟,通过斜叶桨发酵罐单相水体系时搅拌功率计算值与模拟值的比较验证数值模拟的可靠性,并对比2种发酵罐中单相流场分布、固相体积分数分布和功率消耗情况。结果表明:单相水体系时,AFI桨改善了发酵罐内流场结构,搅拌功率较斜叶桨下降40.39%;固液体系时,AFI桨发酵罐内固相体积分数分布更为均匀,罐底沉积现象不明显,搅拌功率较斜叶桨下降17.37%。研究结果为餐厨垃圾厌氧发酵罐搅拌桨的设计与选择提供参考。 相似文献
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文章在不相溶液液两相流搅拌槽内,就三种常用的圆盘涡轮搅拌器,对多层组合桨的搅拌特性进行了数值模拟,分别研究了流场特性、搅拌功率和混合时间。研究表明,多层桨中三种桨型的不同组合,会改变流体最大速度和流场死区的出现位置及影响范围,在不同位置出现封闭的局部小循环,破坏釜内流体的整体循环,并对宏观的混合时间产生较大影响。折叶桨有轴向流,可优先设置在最底层,以消除釜底死区。弯叶桨可产生高速径向流,可优先设置在中间层,利于釜内大循环的形成。多层桨不同桨层间的相互影响,使不同位置的桨叶的功率消耗不一致,现有传统的经验算法不适用于多层组合桨的功率计算,有必要进一步探讨。 相似文献
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搪玻璃反应釜因其良好的防腐性被广泛应用于食品工业中,轴流式搅拌釜具有轴向流动大,循环作用好的优点,是果肉饮料生产、发酵搅拌过程较好的选择。采用数值模拟和试验的方法,研究了挡板对流式搅拌釜内固液悬浮的影响规律。通过试验得出结论:试验中改变转速,可以发现存在一个"临界转速",在该转速之前,无挡板时搅拌轴扭矩更小;而在该转速之后则发现有挡板的情况下搅拌轴扭矩更小,挡板抑制"打漩"效果明显。在此基础上采用大于"临界转速"的转速进行非定常两相混合数值模拟计算,结果表明转速超过"临界转速"后,挡板对于反应釜固液悬浮有促进作用。 相似文献
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目的:探究啮合同向双螺杆挤出机不同螺杆构型对流场的影响,改善聚乳酸的材料性能。方法:应用Solidworks软件建立双头螺纹元件的几何模型,在Polyflow中进行数值模拟,借助Fieldview软件对仿真结果进行后处理分析,并对比剪切速率场、压力场、速度场、黏度场以及停留时间分布曲线RTD,得出螺槽深度对流场的影响。结果:在中心距相同的情况下,通过改变螺纹元件的外径和内径之比改变螺槽深度,在相同的工艺条件下,同向双螺杆流道内各物理场以及混合性能均存在较大差异;与构型二相比,构型一的剪切作用更强,但构型二的建压能力更好;挤出过程中,构型二轴向混合能力较好但自清洁能力较差,而构型一轴向混合能力较差、自清洁能力较好。结论:螺槽深度的改变对流道混合性能有着一定影响且存在规律性,可有效指导双螺杆挤出机螺纹元件的设计。 相似文献
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以一级大豆油为液相、Pt/C催化剂为固相,釜体为圆柱体,釜体高度为180 mm,内径为120 mm,液面高度为130 mm,利用FIUENT软件对大豆油氢化反应釜进行液固两相数值模拟,发现倾斜式搅拌桨距反应釜底部高度80 mm、桨叶直径40 mm、搅拌速率300 r/min时流体流动及催化剂分布最佳,并以模拟的主要参数制备了高压反应釜。高压反应釜内一级大豆油添加量90.0 g、Pt/C催化剂添加量0.15%(m/m),充入8 MPa的CO2气体,后充入H2保持反应釜内总压为12 MPa,通过优化得出最佳反应温度97℃、反应时间87 min、搅拌速率285 r/min时,氢化后大豆油的碘值为79.50 g I2/100 g,说明模拟准确,为展示大型设备油脂氢化过程提供理论依据。 相似文献
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The flow of plasticized maize starch in a co-rotating twin screw extruder was simulated by using computational fluid dynamics (CFD). Sensitivity of the simulation to the selected viscosity model was analyzed. The results suggest that about 16 times increase in zero shear viscosity has no influence on the flow, whereas a slight change in viscosity at the shear thinning region leads to significant increase in pressure drop along the mixing zone of extruder. Simulation results were validated quantitatively by experimental data. Furthermore, the flow type and profile in the extruder were discussed by using the influence of screw speed and screw configuration as exemplary process parameters. To evaluate the dispersive mixing efficiency, material specific critical capillary number was implemented into particle tracking simulations. Maximum shear stress generated at the tip of the screws was used to calculate the maximum capillary ratio, and therefore to determine the dispersive mixing efficiency. The results show that increase in screw speed led to better dispersive mixing, although the generated shear stresses decreased. To investigate the influence of screw geometry, two different screw configurations were simulated. The results show that the dispersive mixing efficiency can be improved by using reverse kneading blocks at which more particles are exposed to high shear stresses. 相似文献
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Computational fluid dynamics investigation of turbulence models for non-newtonian fluid flow in anaerobic digesters 总被引:1,自引:0,他引:1
Wu B 《Environmental science & technology》2010,44(23):8989-8995
In this paper, 12 turbulence models for single-phase non-newtonian fluid flow in a pipe are evaluated by comparing the frictional pressure drops obtained from computational fluid dynamics (CFD) with those from three friction factor correlations. The turbulence models studied are (1) three high-Reynolds-number k-ε models, (2) six low-Reynolds-number k-ε models, (3) two k-ω models, and (4) the Reynolds stress model. The simulation results indicate that the Chang-Hsieh-Chen version of the low-Reynolds-number k-ε model performs better than the other models in predicting the frictional pressure drops while the standard k-ω model has an acceptable accuracy and a low computing cost. In the model applications, CFD simulation of mixing in a full-scale anaerobic digester with pumped circulation is performed to propose an improvement in the effective mixing standards recommended by the U.S. EPA based on the effect of rheology on the flow fields. Characterization of the velocity gradient is conducted to quantify the growth or breakage of an assumed floc size. Placement of two discharge nozzles in the digester is analyzed to show that spacing two nozzles 180° apart with each one discharging at an angle of 45° off the wall is the most efficient. Moreover, the similarity rules of geometry and mixing energy are checked for scaling up the digester. 相似文献