搅拌槽中酯化反应热失控的CFD模拟

热失控是化工过程中常见的安全风险之一。在间歇釜式反应器中,桨叶的机械转动可以增强流体的循环流动、湍流强度、混合程度以及传热,进而有效防范热失控。防控效果与反应器结构和搅拌桨型密切相关。针对丙酸异丙酯酯化反应,采用计算流体力学模拟研究了桨型(Rushton桨、30o PBT桨及60o PBT桨)、转动方向和挡板对釜式反应器内温度演化的影响,从流动结构方面分析了原因。基于散度的失控判据比较了三种搅拌桨抑制热失控的能力,抑制能力为Rushton桨＞30° PBTD桨＞60° PBTD桨。本研究可为搅拌反应器热失控的优化设计提供一定的理论依据。     

Comparison of carbon nanofiller-based polymer composite adhesives and pastes for thermal interface applications

Graphite nanoplatelets (GNP), carbon black (CB) and carbon nanotubes are extensively researched to produce thermal interface materials (TIMs). This work reports comparison of interfacial thermal conductance (ITC) of carbon nanofiller-based polymer composite adhesives and pastes. The results show that total thermal contact resistance (TTCR) of GNP/rubbery epoxy composite was the same as that of an equivalent glassy epoxy composite. Although CB-based rubbery epoxy and silicone composites can be applied as thin bondlines, their TTCRs were significantly higher than GNP/rubbery epoxy. GNP incorporation into CB/rubbery epoxy composite improves the ITC of the CB/rubbery epoxy composites but the performance of CB/GNP/rubbery epoxy was inferior to GNP/rubbery epoxy. The thermal paste of GNP/polyetheramine had TTCR of 4.8 × 10^− 6 m²·K/W which is comparable to commercial TIM-paste. The paste produced with silicone had relatively poor ITC versus that prepared with polyetheramine. The paste having smaller particle sized GNPs offers lower TTCR than that prepared with large sized GNPs. The GNP/rubbery epoxy adhesives produced from precursor pastes gave the lowest TTCRs in comparison with the other adhesives. This study suggests that GNPs offer potential for enhancing ITC of TIMs and that ITC of adhesives depends on fillers' thermal conductivity and their interfacial contact with substrates.     

Influence of short time milling in R5(Si,Ge)4, R = Gd and Tb,magnetocaloric materials

The effect of the short milling times on R₅(Si,Ge)₄ R = Gd, Tb magnetocaloric material properties was investigated. In particular, the effect of milling on atomic structure, particles size and morphology, magnetic, and magnetocaloric effect was studied. With short milling times (< 2.5 h), a reduction of the Gd₅Si_1.3Ge_2.7 and Tb₅Si₂Ge₂ particles size was achieved down to approximately 3.5 μm. For both compositions the main differences are a consequence of the milling effect on the coupling of the structural and magnetic transitions. In the Gd₅Si_1.3Ge_2.7 case, a second-order phase transition emerges at high temperatures as a result of ball milling. Consequently, there is a decrease in the magnetocaloric effect of 35% after 150 min of milling. Interestingly, an opposite effect is observed in Tb₅Si₂Ge₂ where a 23% increase of the magnetocaloric effect was achieved, driven by the enhancement of the coupling between magnetic and structural transitions arising from internal strain promoted by the milling process.     

Achieving the best glass former in a binary Gd–Co alloy system

In this work, the best glass former in a binary Gd–Co alloy system has been designed by thermodynamic parameter γ^⁎, which has been proved to be valid in the prediction of glass forming ability (GFA) of other binary alloys. A metastable phase has been observed in some Gd–Co melt-spun ribbons and its composition has been ascertained. By analyzing the effect of the metastable phase on the GFA of the Gd–Co binary alloys, we predict the Gd₅₀Co₅₀ alloy as the best glass former in the binary alloy system. The prediction has been confirmed by the experimental results, proving the validity of the parameter γ^⁎ in the Gd–Co binary alloys.     

Application of near infrared sensors to preconcentration of hydrothermally-formed copper ore

Near infrared sensors can be a very useful technique for the qualitative analysis of complex ores, and thus could be useful for the preconcentration of ores. In this paper, individual particles of hydrothermally-formed copper ore sampled from a mine in the Los Pozos mining district, northern Chile, were classified as product, middling and waste based on their near infrared response. The classification of copper bearing minerals (product) from gangue (waste) was considered for vibration combination bands at longer wavelengths from 2000 to 2400 nm. This region exhibits characteristic features for carbonates and hydroxyl gangue bearing minerals. The near infrared features at 1400 and 1900 nm were not considered favourable for classification and subsequent discrimination because they can be influenced by moisture and other environmental factors and are easily suppressed by iron-rich minerals.Two near infrared preconcentration strategies were applied for particle discrimination. Results indicate that targeting only the calcite (carbonate) dominated particles for discrimination as waste provided the best option for preconcentration. The near infrared discrimination analysis correlates well with mineralogical (QEMSCAN® and XRD) and elemental (XRF) data classification. The results indicate that near infrared spectroscopy is a suitable preconcentration method for supergene copper ore.     

多级油缸导向套装配问题及解决

油缸产品零件虽然不多,但由于导向套的装配精度直接影响产品的密封性和工作性能,因此对导向套的装配精度要求非常严,特别是煤机行业多级油缸导向套的装配。由于其工作时承载力大,且需要在潮湿的恶劣环境下工作,因此对其导向套的安装精度和密封性的要求更为严格。     

直立锁边金属屋面的特点与应用

在建筑防水结构中,直立锁边金属屋面是最为常见的结构形式。本文指出它的特点是固定方式可满足温度变形的需要,抗风压、防腐耐久、防水、防火、防雷性能好,所使用的压型技术和生产方式灵活,同时具有坚固的装饰板支撑系统,既可作为最外层的装饰面,也可作为单纯的防水屋面。     

开敞式盾构机推进力的计算

介绍了开敞式盾构机构造和工作原理及其与土压平衡盾构机的区别,并对开敞式盾构机的受力情况进行分析,从而总结出推力计算公式。并结合工程实际,对φ6.25m开敞式盾构机的总推力进行计算,为盾构机设计提供了一定参考。     

筛分式双齿辊破碎机轴承密封装置的分析与改进

以筛分式双齿辊破碎机为研究对象,对现有的几种辊轴轴承密封方式进行了对比分析;结合煤矿现场筛分式双齿辊破碎机的实际运转情况,总结筛分式双齿辊破碎机辊轴轴承密封处常常出现的故障,并找出其原因,提出合理有效的改进措施。为筛分式双齿辊破碎机辊轴轴承密封的合理设计提供了参考依据。     

掘锚护一体机的设计研究

为提高掘进效率,同时解决施工安全和劳动强度问题,简述了一种集掘进、锚固、支护功能于一体的新型掘锚护一体机。该设备将锚护结构固定在行走部两侧,通过外筒、中筒、内筒2级伸缩把锚杆机和支护机送至掘进机前部,继而实现零空顶距的锚护作业。该设备可采用手动、遥控2种控制方式进行操作,具有操作灵活、动作可靠等优点。