Turbulence damping above the cloud height in suspensions of concentrated slurries in stirred tanks

Poor mixing in the clear liquid layer above the cloud height has been reported by several authors. This study uses LDV measurements to quantify turbulence above the cloud using a liquid level of 1.5 T to remove the barrier of a free surface at H = T. A D = T/3, down-pumping PBT was used at an off-bottom clearance of C = T/3. Three slurries were tested at impeller speeds 0.8, 1, and 1.2N_js. The change in turbulence was quantified using the normalized root mean square (RMS) of the fluctuating velocity summed and averaged over each radial traverse. A significant difference between the fluctuating values of the cloud height—minimum, average, and maximum—was observed. The turbulence decays until the maximum cloud height. Beyond that, it remains constant and near zero. The effects of both particle size and solids concentration prove to be important.     

Study of filtered interphase heat transfer using highly resolved CFD–DEM simulations

Accurately predicting the complex inhomogeneous heat transfer behavior in gas–solid fluidized beds is of fundamental importance. In this work, we constitute an enhanced filtered interphase heat transfer coefficient (IHTC) closure by systematically filtering the dataset from highly resolved three-dimensional (3D) computational fluid dynamics–discrete element model simulations. Particularly, effects of several potential filtered variable markers on filtered IHTC predictions are examined by statistical analysis. We reveal the formulated filtered IHTC correction closure manifests a systematic dependence on filtered interphase temperature difference as an additional marker. The proposed closure shows good agreement with the filtered fine-grid simulation data in an a priori analysis. Moreover, the difference of filtered IHTC corrections deduced from 3D Euler–Euler and Euler–Lagrange simulations is quantified. Finally, the comparative analysis between our proposed filtered IHTC formulation and those in literature is implemented. This work holds a potential to facilitate the development of thermal gas–solid flow modeling.     

Viscoelastic properties and flow instabilities of aqueous suspensions of cellulosic fibers: Effects of a gelation agent on dispersion,rheology, and flow stability

Processing of concentrated lignocellulosic biomass suspensions typically involves the conversion of the cellulose into sugars and sugars into ethanol. Biomass is usually pretreated via methods like comminution or steam explosion to form fine cellulosic fibers to be dispersed into an aqueous phase for further treatment. The resulting cellulose suspensions need to be pressurized and pumped into and out of various processing vessels without allowing the development of flow instabilities that are typically associated with “demixing”, that is, the segregation of the cellulosic biomass from the aqueous phase via the formation of mats of cellulosic fibers and the filtration of the aqueous phase. Such demixing can prevent continuous processing at high rates. Here, the development of flow instabilities via the demixing effect for cellulose suspensions is demonstrated using capillary and compressive squeeze flows. It is shown that the use of a gelation agent, hydroxypropyl guar gum, at the critical concentration of 0.5 wt% or higher significantly affects the viscoelastic material functions of cellulosic suspensions, improves the dispersive mixing of the fibers within the aqueous phase, and results in the elimination of the flow instabilities and associated demixing effects that are ubiquitously observed during the pressurization and processing of cellulosic suspensions.     

PREPARATION OF SILVER POWDER FOR CONDUCTIVE PASTE

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钠基膨润土对硅溶胶涂料悬浮性的影响

硅溶胶涂料以其良好的工艺性能在熔模铸造领域得到越来越广泛的应用，但在实际使用过程中该涂料也存在着悬浮性不良等问题，影响到涂料实际使用。分析了改善硅溶胶涂料悬浮性的机理，以及硅溶胶涂料悬浮性与流杯粘度及涂片厚度等工艺性能之间的关系。采用钠基膨润土改善硅溶胶涂料的悬浮性，并取得了良好效果。     

粘土砂湿型用醇基涂料及其应用

粘土砂湿型铸造,铸件表面容易产生粘砂。某厂采用粘土砂湿型生产拖拉机铸件,也遇到了铸件表面粘砂的问题。通过不断选择醇基涂料悬浮剂,调整涂料的配比,最后采用SN-1悬浮剂,经试验和应用取得较好的效果。     

新型纳米分散剂提高醇基涂料悬浮稳定性的研究

对用新型纳米分散剂提高醇基涂料悬浮稳定性进行了研究 ,试验结果表明 ,只有新型纳米分散剂和有机助剂配合使用 ,才可取得明显的悬浮效果 ,醇基涂料的 2h、 2 4h、 48h和 72h悬浮率分别达到 99%、 98%、 96 %和 94%。这种醇基涂料还具有强度高、发气量低、涂刷性好和点火不起泡等特点。     

MATLAB在汽车半主动悬架仿真中的应用

介绍了利用MATLAB软件建立汽车的二自由度数学模型。并建立了基于参考模型的模糊及PID控制器，通过应用SIMULINK对比仿真，得出了模糊控制器对于汽车半主动悬架的控制效果要优于PID控制器。     

刚度和阻尼可调前桥油气悬架的设计

根据CF700型号拖拉机前桥悬架的参数要求,设计一种刚度和阻尼均可调的油气悬架系统。建立油气悬架刚度和阻尼的数学模型,计算油气弹簧的结构参数,仿真研究油气弹簧不同工作状态下的动刚度、阻尼力和输出力的特性以及各结构参数变化对油气弹簧输出力特性的影响。结果表明:油气弹簧液压缸有杆腔和无杆腔连通时阻尼力和悬架输出力较小,两腔分离时阻尼力和悬架输出力较大,通过调节两腔连通时节流面积的大小,可以调节悬架阻尼力和输出力;通过额外连通一个蓄能器,明显减小了油气弹簧的动刚度和悬架的输出力;比例阀节流孔径的大小影响悬架的阻尼力和输出力,节流孔径越大,悬架阻尼力和输出力越小。所设计的油气弹簧可以实现悬架"软"、"硬"状态的切换,并能在一定范围内对悬架刚度和阻尼进行调节。将油气悬架的刚度和阻尼系数线性化后代入振动仿真模型,得到前桥悬架拖拉机座椅安装位置垂向振动加速度均方根值、俯仰振动角加速度均方根值及前轮动载荷均方根值分别降低了9.2%、42.4%、70.3%,提高了拖拉机的行驶安全性和乘坐舒适性。该研究为后期开发半主动油气悬架提供重要理论依据。     

电动静液压作动器EHA及其在汽车主动悬架中的应用

将电动静液压作动器EHA(Electro-Hydrostatic Actuator)应用于汽车主动悬架中, 并提出了基于EHA的主动悬架样机结构.同时,建立了1/4汽车主动悬架动力学模型,设计了用于EHA主动悬架的模糊控制器,并进行了仿真和实验研究.结果表明,基于EHA的模糊控制主动悬架明显改善了汽车的平顺性和操纵稳定性.