Interactions between hybrid nanosized particles and convection melting inside an enclosure with partially active walls: 2D lattice Boltzmann-based numerical investigation

The ice melting is investigated inside a square cavity with two isothermally partially active walls. The concept of dispersing hybrid alumina–Cu nanoparticles and hybrid silica–multiwalled carbon nanotubes (MWCNTs) nanoparticles is recommended for thermal performance enhancement in this thermal energy storage (TES) system. The two-dimensional explicit lattice Boltzmann convection melting scheme in the single-phase model is applied to account for the natural convection flow induced in the melt region and evolution of the solid–liquid interface. The complete melting time for the pure phase change material (PCM) using case (II) is 33.3% lower compared with other cases. If the price of hybrid Al₂O₃–Cu nanoparticles and heat storage capacity is important, the full melt time diminishes by 16.6% with a volume fraction of 0.01 in case (II). Once hybrid silica–MWCNT nanoparticles with a volume fraction of 0.01 are utilized inside case (II), the lowest charging time is achieved. The complete melting time abates by 23.66% in contrast to the pure PCM melting. The use of single/hybrid nanoparticles to enhance the PCM melting is not necessarily economical as efficient positions of active parts could further lessen the charging time. The efficiency of hybrid nanoparticles is linked to the type and weight proportions of nanoparticles, and positions of thermally active parts.     

Mixed convective heat transfer enhancement in a ventilated cavity by flow modulation via rotating plate

The present study numerically explores the mixed convection phenomena in a differentially heated ventilated square cavity with active flow modulation via a rotating plate. Forced convection flow in the cavity is attained by maintaining external fluid flow through an opening at the bottom of the left cavity wall while leaving it through another opening at the right cavity wall. A counter-clockwise rotating plate at the center of the cavity acts as an active flow modulator. Moving mesh approach is used for the rotation of the plate and the numerical solution is achieved using arbitrary Lagrangian-Eulerian finite element formulation with a quadrilateral discretization scheme. Transient parametric simulations have been performed for various frequency of the rotating plate for a fixed Reynolds number (Re) of 100 based on maximum inlet flow velocity while the Richardson number (Ri) is maintained at unity. Heat transfer performance has been evaluated in terms of spatially averaged Nusselt number and time-averaged Nusselt number along the heated wall. Power spectrum analysis in the frequency domain obtained from the fast Fourier transform analysis indicates that thermal frequency and plate frequency start to deviate from each other at higher values of velocity ratio (>4).     

非线性状态下饱和紧密砂土的孔隙压力估算

介绍了无限土体中球孔扩张理论,以及在高应力状态下,考虑材料非线性时紧密砂性土的八面体应力及极限承载力解答,推演出了在非线性饱和紧密砂土内,球孔扩张压力下的孔隙压力公式,并分析了其分布特性。     

斜梯形锥螺纹联接强度计算方法探讨

介绍了螺纹的种类和分类方法以及斜梯形锥螺纹的主要应用场合,并着重介绍了斜梯形锥螺纹联接强度的计算方法、斜梯形锥螺纹与三角形锥螺纹的受力强度比较。分析了斜梯形锥螺纹牙形承受轴向拉力的能力要比三角形锥螺纹要强的原因。     

喷射混凝土衬砌爆破损伤的数值分析

根据混凝土损伤的基本理论，把混凝土分段曲线损伤模型应用到喷射混凝土衬砌的有限元分析中。利用APDL语言编程对ANSYS进行二次开发．模拟了地下工程构建过程中，掘进爆破冲击波对喷射混凝土衬砌的损伤影响程度。实例计算考虑了不同条件下混凝土衬砌的最大损伤值及损伤积累发展趋势。按照5％的允许损伤准则，求出了不同条件下的最大炸药用量，为地下工程掘进施工提供了理论依据。     

磁黄铁矿的同质多象变体及其选别性质差异

有色金属矿中常伴生一种或多种变体磁黄铁矿，不同变体磁黄铁矿的选别性质不尽相同。本文采取多种测试分析方法，探讨磁黄铁矿的成分变化与晶体结构变化的关系，以及不同变体磁黄铁矿的磁性，可浮性变化的特征。     

无底柱分段崩落法崩落矿石形态及其影响研究

本文针对无底柱分段崩落法存在的问题，从爆破入手，对放矿对象──崩落矿石的形态及其对矿石损失贫化的影响进行了理论分析、小型试验和工业试验，提出了矿石崩落体的概念，确定了崩落体的形态，指出放出体──松动体──崩落体是相互联系的整体，研究放矿问题应把放矿和爆破崩矿进行综合研究，通过爆破控制崩落体的形态和效果，使放出体与矿石崩落体和残留体构成的矿堆形态相吻合，以降低矿石损失贫化。     

铝铸轧铸嘴型腔的计算机仿真设计

采用一个k-e低雷诺数紊流模型建立铸嘴型腔三维流动与传热的数学模型,通过对分流块几何尺寸、数目、形状影响铸嘴型腔熔体出口速度和温度的计算机仿真,得知分流块几何尺寸减小可以明显降低铸嘴型腔出口处熔体速度相对误差,使熔体温度沿铸嘴宽度方向分布更均匀。因此,在保证铸嘴结构刚度的前提下,应尽量延长型腔长度以及减小分流块尺寸。     

S200M型掘进机回转台铸造工艺探讨

回转台是S2 0 0M掘进机关键部件 ,尺寸大、结构复杂 ,是掘进机上受力最大的零件。通过严谨的铸造工艺设计和严格的生产过程控制 ,可有效地防止回转台的铸造毛坯件产生铸造裂纹、缩孔、夹杂等缺陷 ,保证铸造质量     

机械密封环隔离体法有限元分析

针对动静环整体建模繁琐及求解计算量大的缺点,采用隔离体法思路对动静环分开建模、加载和计算,将计算结果通过数值方法加以整合,并从中找到与实际整体运行过程中相符的计算结果以便于进行推断,具有较好的可行性和可取性。