90°弯管内示踪气体混合均匀性的数值模拟与实验研究

示踪气体在管道内的混合均匀性,对示踪法测量气体流量的准确性或者在线校准管道气体流量计的校准精度影响很大.在直径为300mm的90°弯曲管道内,对示踪气体CO与空气的混合情况进行了数值模拟研究,并与实验结果进行了对比分析.结果表明,五孔释放混合效果明显要好于单孔释放,且五孔释放时弯管下游9D处示踪气体与空气混合基本均匀.数值模拟结果和实测结果基本吻合,可为示踪法测量气体流量和在线校准管道气体流量计提供参考.     

人-车系统的人体乘坐舒适性仿真及实验研究

汽车振动直接影响人体的乘坐舒适性.为了高效地评价振动环境下人-车系统的人体乘坐舒适性,运用ADAMS/View和LifeMOD软件构建了人-车系统生物力学仿真模型,通过对路面不平度的模拟,将不同路面作为振动激励添加到人-车系统的动力学分析当中,进行不同路面及不同车速的人体乘坐舒适性仿真研究.在SA30-S802/ST随机振动台上,进行相应路面及车速激励的人体振动响应实验,并验证了人体乘坐舒适性.将仿真计算与实验结果进行对比研究表明,仿真结果和实验结果基本一致,一定程度验证了所建立的人-车系统生物力学仿真模型的正确性及其进行人体乘坐舒适性仿真的可靠性,对快速评价人-车系统的人体乘坐舒适性具有一定的指导价值,为在汽车产品的设计阶段进行人体乘坐舒适性预测和评价提供了有效方法.     

数值模拟在陶瓷粉末材料冷等静压过程中的应用

为了解释陶瓷粉末件低密度缺陷的形成原因，借助有限元分析软件MSC.MARC对陶瓷粉末件的冷等静压（CIP）形成过程进行了有限元数值模拟，从数值计算的角度给出了成形过程中粉体的应变分布、密度分布规律，并提出了改善陶瓷粉末体件低密度现象的对策，研究结果表明：在CIP成形过程中芯棒顶端倒角处变形受到抑制，等效应变最大，相对密度最小，出现变形不均匀现象；粉末构件的几何形状、尺寸、模具形状对低密度区域的形成有较大影响。     

粉体混合均匀性定量评估模型的建立与研究

针对粉体混合均匀性难以快速准确检测和定量化描述的问题,通过大量实验采用分形理论建立了粉体混合均匀度定量评估模型,即数出不同半径圆内包含的粉体颗粒数,在双对数坐标上找出"数目-半径"或"数目-质量"点,与理论计算的标准线比较来说明粉体混合的均匀程度。当不同粒径的粉体混合,用"数目-半径"分析法;同粒径的粉体混合,用"数目-质量"分析法。同时提出了定量评估粉体混合的不均匀程度,特别适合于现场检验。     

DEM simulation for optimal design of powder mixing in a ribbon mixer

A ribbon mixer is often employed in powder mixing in a wide range of engineering fields. The structure of the ribbon mixer is extremely complicated. This structure makes it difficult to understand the mixing mechanism by experimental approaches due to problems related to accurate sampling. At present, the mixing mechanism in the ribbon mixer is empirically identified as convection, despite a lack of precise assessment. Additionally, experimental investigations to find the optimal design of the ribbon mixer have not been sufficiently conducted because of its prohibitive cost. As such, there is a lack of sufficient discussion concerning the design for better mixing in the ribbon mixer. Numerical technologies represent a promising approach for solving the aforementioned problems. Significant improvements in computer hardware have enabled numerical models such as the discrete element method (DEM) to be positively employed in powder mixing. In the current study, an identification approach is developed for convective mixing, and besides, the study explores an effective parameter for better mixing in the ribbon mixer using the DEM. A swept volume measurement approach due to paddle movement is newly developed to identify the main mixing mechanism as convection. Sensitivity analyses are performed to find an effective parameter for better mixing. Through the sensitive analyses, the blade width is indicated as an important factor for achieving better mixing. Moreover, this study shows that the relationship between the swept volume and mixing index remains, even if the paddle width changes. Thus, the swept volume measurement method is revealed as useful for identifying the mechanism as convection in the ribbon mixer. Thus, not only novel finding regarding the blade width for better mixing but also the development of an approach for identifying convective mixing in the ribbon mixer is presented herein. Incidentally, convection being the dominant mechanism is consistent with the novel finding regarding blade width achieving better mixing.     

Vortex simulation of turbulent mixing layers

We present here a brief survey of vortex-dynamical simulations of the plane mixing layer using different forms of vortex elements. Points and blobs, which have been widely used in the past, suffer from irregular evolution of the vortex sheet approximating the shear layer, and the rather long time-averaging required to obtain meaningful statistics. A technique recently proposed by the authors, using vortex arcs or sheet elements, has been found to be helpful in avoiding these difficulties. In particular, this technique avoids the singularity in induced velocity associated with point vortex techniques, and is therefore in no need of any form of the “desingularization” that is often introduced in the latter. New results for excited mixing layers using the vortex sheet element model are presented, and are shown to be in good agreement with experimental observations.     

示踪气体混合均匀性的试验研究

为探讨示踪气体与被测气体实现均匀混合的条件,以CO作为示踪气体,以空气作为被测气体,在直径为0.300 m的90°弯曲管道内对示踪气体与空气的混合均匀性进行了试验研究.结果表明,在本试验条件下,当混合气体流速大于3.2 m/s时,在弯管下游的12D(D为管道内径)和15D处,示踪气体的径向和轴向平均体积分数误差小于4%,示踪气体的实测平均体积分数与理论值趋于一致,可认为示踪气体与空气的混合达到了均匀.因此,工业气体的管道输送过程中采用示踪法校准气体流量计时,可在满足上述条件的位置处作为取样点.     

现场混装乳化炸药静态敏化器混合特性研究

为了研究现场混装乳化炸药静态敏化器的混合特性以及安全性,釆用数值模拟和试验相结合的方法,分析了设计的静态敏化器的混合机理、参数变化对混合流场特性的影响规律以及其混合安全性,对比分析了两种混合单元组合方式下乳化基质与敏化剂的混合效果。研究表明:两种不同结构的混合单元能起到让乳化基质与敏化剂初步混合和强化混合的作用;当乳化基质、敏化剂混合流流经静态混合单元时,压力值在乳化基质管路安全泵送的压力范围内,应用安全;在两个缩径混合单元中间加一个网状结构混合单元组成的静态敏化器具有良好的混合敏化效果。     

二氧化钛复合微粉的抗菌性能研究

采用混合－灼烧法制备二氧化钛复合微粉，研究组成，含量和温度对二氧化钛复合微粉抗菌性能的影响。     

内嵌式钨铜粉末爆炸复合结构材料的研究

为满足托克马克核聚变装置内壁材料对W-Cu复合材料的需求,提出了内嵌式粉体爆炸复合方法和技术工艺。先用该方法制备内嵌式W-Cu粉复合材料,其实验粉末分别采用粒径3μm与23μm的纯钨粉和添加10%铜粉的W-Cu混合粉末(质量分数)。然后利用扫描电子显微镜、显微硬度计对内嵌式W-Cu粉复合材料进行表征、分析。结果显示,实验粉末经过爆炸烧结压实后能达到90%以上该密实材料的密度。添加10%铜粉后制备的W-Cu粉复合结构材料结合界面更加规则均匀理想,结合界面附近几乎没有孔隙,粉末压实部分孔隙度更小且孔隙的尺寸更小,均匀致密性更好,但粉末压实层硬度更低。使用粒径3μm的混合粉末与23μm的混合粉末,后者制备的W-Cu粉复合材料,粉末压实部分均匀致密性更好,孔隙度更小且孔隙的尺寸更小,粉末压实层密度更大,但硬度更低。     

内嵌式钨铜粉末爆炸复合结构材料的研究

为满足托克马克核聚变装置内壁材料对 W-Cu复合材料的需求,提出了内嵌式粉体爆炸复合方法和技术工艺。先用该方法制备内嵌式W-Cu粉复合材料,其实验粉末分别采用粒径3μm与23μm的纯钨粉和添加10%铜粉的W-Cu混合粉末(质量分数)。然后利用扫描电子显微镜、显微硬度计对内嵌式 W-Cu粉复合材料进行表征、分析。结果显示,实验粉末经过爆炸烧结压实后能达到90%以上该密实材料的密度。添加10%铜粉后制备的 W-Cu粉复合结构材料结合界面更加规则均匀理想,结合界面附近几乎没有孔隙,粉末压实部分孔隙度更小且孔隙的尺寸更小,均匀致密性更好,但粉末压实层硬度更低。使用粒径3μm的混合粉末与23μm的混合粉末,后者制备的 W-Cu粉复合材料,粉末压实部分均匀致密性更好,孔隙度更小且孔隙的尺寸更小,粉末压实层密度更大,但硬度更低。     

Finite element simulation of the effects of process parameters on deposition uniformity of chemical-vapor-deposited silicon carbide

A two-dimensional model was developed to simulate chemical vapor deposition process for preparing SiC coating by MTS + H₂ system in a vertical hot-wall reactor. The effects of process parameters, including deposition temperature, the flux of mixed gases, the ratio of H₂ and Ar, and the volume ratio of MTS and mixed gases, on deposition uniformity of SiC coating were calculated by finite-element method. The CVD process was optimized by an orthogonal L₉(3)⁴ test to deposit uniform SiC coating. The results show that the deposition uniformity of SiC is influenced greatly by the deposition temperature and the ratio of H₂ and Ar, and little by the flux of mixed gases and the volume ratio of MTS and mixed gases. The optimal deposition uniformity of SiC can be obtained under the operating condition as follows: deposition temperature 900 °C, the flux of mixed gases 0.6 l/min, H₂: Ar = 1:0, and the volume ratio of MTS and mixed gases 1:10. Part of calculated results is validated by corresponding experimental data, which implies that this model is valid and reasonable to characterize CVD process of SiC coating.