MVR蒸汽离心风机的数值模拟与结构优化

为了进一步提高MVR蒸汽离心风机的运行性能,对蒸发负荷为15 t/h的MVR蒸汽离心风机进行气动热力学设计,建立了三维物理模型;采用CFD数值模拟手段,对MVR蒸汽离心风机内部流场进行数值模拟研究,研究了风机内部结构参数:集流器末端与叶轮入口径向间隙大小、集流器末端深入叶轮的深度、蜗壳宽度与叶轮出口宽度比对风机性能的影响,并对风机结构进行了优化。研究结果表明:集流器与叶轮入口径向间隙大小与风机效率成单调下降关系,间隙越小,效率与全压越大;当集流器末端深入叶轮的深度在10—30 mm之间时,MVR蒸汽离心风机的效率均可保持在75.7%左右;当蜗壳宽度与叶轮出口宽度比为4.47时,风机效率提高1.4%,全压提高1.8%;MVR蒸汽离心风机进出口压力的模拟值与实验值进行了比较,二者吻合较好。     

不同溶剂重结晶RDX对A5混合炸药压药成形性能的影响

通过对A5混合炸药压药成形性能的研究,分析了由于RDX在不同溶剂中的结晶机理不同,造成RDX的压药成形性能不同,从而导致了A5混合炸药压药成形性能的改变。对RDX及其以RDX为主体的混合炸药的应用具有指导意义。     

激光熔覆工艺参数对高熵合金涂层性能的影响及其优化

采用同步送粉激光熔覆技术在Q235钢表面制备了CoCrFeNiMo高熵合金涂层。采用单因素试验研究了工艺参数对涂层形貌及性能的影响,并分析了其作用机理。通过正交试验得到最优工艺参数为:激光功率1000 W,进给速率4.5 mm/s,搭接率35%。此时涂层的平整度标差为0.036 mm,显微硬度为308.98 HV,平均腐蚀速率为0.0178 g/(m²·h)。结果表明,在试验范围内,涂层的平整度随着激光功率、进给速率和搭接率的提升得到改善,显微硬度和耐蚀性的变化趋势相同,它们与工艺参数对显微组织的影响相关。     

鼓风式机械通风冷却塔数值模拟分析及优化

针对鼓风式机械通风冷却塔的研究比较少,现有的规范对其设计也没有明确的规定,采用CFD技术对鼓风式逆流式机械通风冷却塔群的塔排间距、出口速度、环境风及周边建筑物对湿空气回流率的影响进行了模拟计算.计算结果表明:塔排间距减小,回流率增高;冷却塔的出口流速增大塔的回流率减低;当冷却塔周围建筑较远时,冷却塔排布置宜将长轴与主导...     

适用于动物细胞培养的搅拌桨及其数值模拟

提出了一种方法考察桨叶在动物细胞培养上的适用性,应用计算流体力学软件CFX综合比较在30 L搅拌槽中4种不同桨叶的流场、剪切率、Kolmogorov尺度和混合时间,并进行PIV实验验证。结果表明,在单层搅拌体系80 r/min转速下,象耳桨和螺旋桨性能能满足细胞培养要求,Rushton桨在细胞培养罐放大时可以考虑,45°四折叶桨能够适用于细胞培养,但效果不如象耳桨与螺旋桨,PIV实验验证了模拟结果可行性。     

MVR蒸发器管内沸腾传热传质数值模拟

建立了MVR升膜循环蒸发器管内沸腾蒸发传热传质三维物理模型,采用标准k-ε湍流模型、多相流混合模型和C语言编写气液两相之间质量传递和能量传递的自定义函数,对光管和波纹管内氨基酸废水溶液的沸腾蒸发传热传质特性进行了数值模拟研究,得到了光管和波纹管内湍流强度、温度场、相变含气率和平均沸腾传热系数的分布规律,比较了光管和波纹管内流体的流动和传热传质特性,分析了不同管壁加热温度和进口流速对沸腾传热性能的影响。结果表明,采用MVR升膜循环蒸发器可以实现氨基酸废水溶液的低温负压沸腾蒸发操作,传热管的结构对流体的流动和传热传质有影响,波纹管与光管相比可使平均沸腾传热系数提高2.2倍。     

热管换热器流动与传热的CFD模拟及试验

根据热管换热器结构特点及传热特性,建立了热管换热器壳程流动与传热的三维物理模型。模型中引入了多孔介质模型中的分布阻力和分布热源的概念,通过CFD计算软件模拟研究了热管换热器压力降与温度场分布,模拟研究结果与试验结果吻合良好,为热管换热器的进一步理论研究和推广应用提供了依据。     

One-step electrodeposition synthesis and electrochemical properties of Cu6Sn5 alloy anodes for lithium-ion batteries

Cu₆Sn₅ alloys were successfully electrodeposited on rough Cu foils and smooth Cu sheets using a facile one-step electrodepositing method, and their structural and electrochemical properties were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charging/discharging testing and electrochemical impedance spectroscopy (EIS). The influence of surface morphology of the current collectors on the cycleability and the interfacial performance of the Cu₆Sn₅ alloy electrode are both discussed. The results demonstrate that the Cu₆Sn₅ alloy electrode on the rough Cu foil presented better electrochemical performance than that on the smooth Cu sheet because its rough surface could buffer the volume changes to some extent. The first discharging (lithiation) and charging (delithiation) capacities were measured at 462 and 405 mAh g⁻¹ respectively with high initial coulomb efficiency of 88%, with charging capacity in the 50th cycle remaining 76% of that in the first cycle. The phase transformation during initial lithiation was detected by electrochemical impedance spectroscopy (EIS) and its trend versus electrode potential is also discussed.     

Synthesis of microcrystalline brownmillerite Ca2(Al,Fe)2O5 and its influence of mechanical properties to the class G oil-well cement

This study investigated the use of calcium oxide (CaO), aluminum oxide (Al₂O₃) and ferric oxide (Fe₂O₃) as raw materials for the production of brownmillerite Ca₂(Al,Fe)₂O₅, after firing at 1330, 1350 and 1370 °C. Lithofacies analysis, SEM/EDS and XRD were used to analyze the phase transition and microstructure of the clinkers during the firing process, and the contents of free calcium oxide (f-CaO) in the clinkers were determined by chemical titration. The results showed that the optimum temperature for the preparation of brownmillerite was 1370 °C (within the selected temperature range). By firing and quenching, microcrystalline brownmillerite (MB) was obtained (crystallinity index was 0.7). Compared with the compressive strength of class G oil-well cement matrix (M0) without MB, the compressive strength of specimens (M4) with 4 wt% MB addition increased by 67, 12, 20 and 33% (after curing for 1, 3, 7 and 14 d, respectively). meanwhile, the elastic modulus of M4 (after curing for 7 d) was reduced by 24% relative to that of M0, indicating that the mechanical properties of M4 were better than that of M0. To investigate the effect of microcrystalline brownmillerite on the strength and toughness of the class G oil-well cement matrix, triaxial testing was used in this study, and the toughening mechanisms were established.     

Numerical simulation of the dynamic flow behavior in a bubble column: A study of closures for turbulence and interface forces

Numerical simulations of the bubbly flow in two square cross-sectioned bubble columns were conducted with the commercial CFD package CFX-4.4. The effect of the model constant used in the sub-grid scale (SGS) model, C_S, as well as the interfacial closures for the drag, lift and virtual mass forces were investigated. Furthermore, the performance of three models [Pfleger, D., Becker, S., 2001. Modeling and simulation of the dynamic flow behavior in a bubble column. Chemical Engineering Science, 56, 1737-1747; Sato, Y., Sekoguchi, K.,1975. Liquid velocity distribution in two-phase bubble flow. International Journal of Multiphase Flow 2, 79-95; Troshko, A.A., Hassan, Y.A., 2001. A two-equation turbulence model of turbulent bubbly flows. International Journal of Multiphase Flow 27, 1965-2000] to account for the bubble-induced turbulence in the k-ε model was assessed. All simulation results were compared with experimental data for the mean and fluctuating liquid and gas velocities. It is shown that the simulation results with C_S=0.08 and 0.10 agree well with the measurements. When C_S is increased, the effective viscosity increases and subsequently the bubble plume becomes less dynamic. All three bubble-induced turbulence models could produce good solutions for the time-averaged velocity. The models of Troshko and Hassan and Pfleger and Becker reproduce the dynamics of the bubbly flow in a more accurate way than the model of Sato and Sekoguchi. Based on the comparison of the results obtained for two columns with different aspect ratio (H/D=3 and H/D=6), it was found that the model of Pfleger and Becker performs better than the model of Troshko and Hassan, while the model of Sato and Sekoguchi performs the worst. It was observed that the interfacial closure model proposed by Tomiyama [2004. Drag, lift and virtual mass forces acting on a single bubble. Third International Symposium on Two-Phase Flow Modeling and Experimentation, Pisa, Italy, 22-24 September] performs better for the taller column. With the drag coefficient proposed by Tomiyama, the predicted slip velocity agrees well with the experimental data in both columns. The virtual mass force has a small influence on the investigated bubbly flow characteristics. However, the lift force strongly influences the bubble plume dynamics and consequently determines the shape of the vertical velocity profile. In a taller column, the lift coefficient following from the model of Tomiyama produces the best results.