温差与压力驱动下球在冰中的接触熔化运动

分析了圆球下的冰在压力与温差共同作用下产生的熔化过程。利用接触熔化理论和水在三相点附近熔点随压力增加而降低的热物性,求得熔化边界层厚度的表达式、作用力与熔化速度关系所应满足的基本方程,由此可推导得温差和压力单独作用下的接触熔化结果。通过分析讨论发现,1)在压力产生的相同温差条件下,球的压力熔化速度要小于温差驱动接触熔化的速度。温差与压力单独驱动下的各自熔化结果,不能通过温度替换来得到。2)混合驱动下的接触熔化结果不是温差与压力熔化各自结果的叠加。     

三质点共线碰撞问题的理论分析

以三质点弹性碰撞系统为例，考虑质点之间相互作用时局部的接 触变形信息，并基于矩阵函数理论得到了三质点弹性碰撞系统Hamilton空间中的严格理论 解. 基于理论分析结果，详细讨论了不同质点之间的质量比以及接触刚度比对质点碰撞后的 动力学行为的影响，包括可能产生的不同分离模式，接触点的分离次序，以及由此可能导致 的内碰撞现象等.     

从苍蝇与物面的触粘看尺度效应

苍蝇与光滑硬物体接触时，靠腿上纤毛与物体表面产生吸附作用，在JKR接触理论下，得出考虑表面能作用时的粘附力表达式，结果表明芬蝇与物面的触粘和脱脱离界定了其纤毛的尺度范围，该尺度范围与扫描电镜观察的结果相一致。     

线接触弹性接触变形的解析算法

以一般光滑性体接触理论为基础,结合有限长弹性体接触的特点,求出线接触弹性接蟹变形的解析公式,并发现其解析解与数值解具有很好的一致性,所得公式可以对赫兹线接触理论加以补充,与经验公式相比,它能够确切反映材料、载荷以及曲率半径等对接触变形的影响,为工程中的精确计算提供了方便。     

考虑摩擦作用时对具有集中弯矩作用下梁接触规律的研究

对作用有集中弯矩及均布载荷的梁接触问题，只有摩擦系数超过某个临界值时，接触区可以扩展达到集中弯矩作用处，但触区不能超过该点。     

考虑榫接接触刚度的叶轮耦合振动特性计算方法研究

对叶片轮盘典型榫接结构的接触刚度进行了分析,给出了叶轮间接触刚度的计算方法;建立了叶片轮盘榫接耦合计算模型,采用对称循环分析方法对叶轮进行振动特性计算,得到叶轮耦合结构在不同工作转速下的振型及频率;对叶轮耦合结构进行锤击模态试验得到实际频率值。本文计算值与实测值在前3阶的相对误差分别为2.38%、1.58%、3.18%,误差均较小,验证了本文方法的可行性。     

失重状态下旋转液体液面形状分析

本文研究失重状态下圆柱形贮箱内稳态旋转液体的液面形状,液面和贮箱的上下底面相接触.导出了液面形状的计算公式,分析了液面不破裂条件及临界转速,并给出了液面与贮箱底面接触半径及液面中心半径的确定方法.     

依兰陨石坑形成过程数值模拟研究

基于iSALE-2D仿真代码对依兰陨石坑的形成过程进行了研究,采用欧拉算法开展数值模拟,探讨了依兰陨石坑的撞击条件,统计分析了成坑过程中熔化层的形成与分布规律,结合点源成坑相似律模型,拟合得到强度机制下的成坑半径关系式。研究结果表明一颗直径120 m、撞击速度12 km/s的花岗岩质小行星垂直撞击地表形成一个与依兰陨石坑形态相似的陨石坑,再现了成坑形成的3个阶段：接触与压缩阶段、开坑阶段、后期调整阶段。大部分熔体在坑底呈分层堆叠分布,少量熔体随抛射物沉积在靶体表面,呈离散状分布,完全熔化材料质量约为撞击体质量的24倍。直径120 m、撞击速度12 km/s工况模拟结果与拟合的成坑半径关系式结果相对误差10.3%。     

基于数字图像相关方法的矿用扁平接链环模型接触变形实验研究

采用分割辅助数字图像相关方法,针对矿用扁平接链环模型在多齿啮合状态下的接触变形进行了实验分析,测量了该结构在承受拉伸载荷时的全场变形分布,并对其接触面附近区域的应变集中现象进行定性与定量分析。实验以Φ26mm×92mm规格的梯齿型接链环模型为研究对象,提出了相应的多分辨率方法进行接触变形场测量。方法中仅采用单个相机实现多分辨率测试,从而避免了传统多分辨率方法中的图像修正误差。采用降采样后的图像计算试件的全场变形,以实现高效的应变分布分析以及应变集中区域定位;采用高分辨率图像进行局部变形计算,以分析应变集中区域的变形分布。实验结果表明,接链环第Ⅱ对和第Ⅲ对啮合齿的齿根部发生的变形最大,是接链环的薄弱部位。该实验结果为梯齿型接链环的变形规律分析和结构设计提供了有效的实验依据。     

用简单拉伸试验测量材料热力学参数的一种尝试

本文根据变形功与熔化热能的关系,将简单拉伸实验方法推广应用到了熔化热能和变形热效应的测量上。按简单拉伸实验方法测得的熔化热能与热力学的测量结果吻合较好。该研究实现了力学实验方法与物理实验方法的互换,因此,具有重要的实际应用价值。     

Effects of the number and distribution of fins on the storage characteristics of a cylindrical latent heat energy storage system: a numerical study

A numerical study of the effects of the number and distribution of fins on the storage characteristics of a cylindrical latent heat energy storage system (LHESS) was conducted. Due to the low thermal conductivity of phase change materials (PCMs) used in LHESS, fins were added to the system to increase the rate of heat transfer and charging. Finite elements were used to implement the developed numerical method needed to study and solve for the phase change heat transfer (melting of PCM) encountered in a LHESS during charging. The effective heat capacity method was applied in order to account for the large amount of latent energy stored during melting of the PCM and the moving interface between the solid and liquid phases. The effects of increasing the number and distribution of fins on the melting rate of the PCM were studied for configurations having between 0 and 27 fins for heat transfer fluid (HTF) velocities of 0.05 and 0.5?m/s. Results show that the overall heat transfer rate to the PCM increases with an increase in the number of fins irrespective of the HTF velocity. It was also observed that the total amount of energy stored after 12?h increases nearly linearly with the addition of fins up to 12 fins; further addition of fins increasing the total energy stored by ever smaller amounts.     

Solidification and melting heat transfer to an unfixed phase change material (PCM) encapsulated in a horizontal concentric annulus

The solidification and melting process of an unfixed PCM between two isothermal concentric horizontal cylinders was investigated by experimental techniques and by a combined analytical and numerical method. During the solidification process concentric solid PCM layers form at both tube walls, growing slowly into the annulus. Assuming quasi-steady heat conduction, this process is described by a simple analysis. The melting PCM reveals a different behaviour. Due to gravitational forces the solid phase moves downwards. Experiments prove that the solid retains contact with the lower part of the outer tube as well as with the upper part of the inner tube. In this process thin liquid films form between the solid body and the heated walls and heat transfer by conduction is the dominating mechanism during melting. Heat transfer by natural convection causes the melting at the upper interface. There, the melting rates, however, are comparatively small. The theoretical approach and the numerical analysis are based on a balance of the pressure forces in the thin liquid films and of the gravitational force acting on the solid material. As a result melting rates and heat fluxes may be predicted. For practical application a Nusselt correlation is derived.     

Effects of the heat transfer fluid velocity on the storage characteristics of a cylindrical latent heat energy storage system: a numerical study

A numerical study of the effects of the thermal fluid velocity on the storage characteristics of a cylindrical latent heat energy storage system (LHESS) was conducted. Due to the low thermal conductivity of phase change materials (PCMs) used in LHESS, fins were added to the system to increase the rate of heat transfer and charging. Finite elements were used to implement the developed numerical method needed to study and solve for the phase change heat transfer (melting of PCM) encountered in a LHESS during charging. The effective heat capacity method was applied in order to account for the large amount of latent energy stored during melting of the PCM and the moving interface between the solid and liquid phases. The effects of the heat transfer fluid (HTF) velocity on the melting rate of the PCM were studied for configurations having between 0 and 18 fins. Results show that the overall heat transfer rate to the PCM increases with an increase in the HTF velocity. However, the effect of the HTF velocity was observed to be small in configurations having very few fins, owing to the large residual thermal resistance offered by the PCM. However, the effect of the HTF velocity becomes more pronounced with addition of fins; since the thermal resistance on the PCM side of the LHESS is significantly reduce by the large number of fins in the system.     

Analytical model for melting in a semi-infinite PCM storage with an internal fin

The most PCMs with high energy storage density have an unacceptably low heat conductivity and hence internal heat transfer enhancement techniques such as fins or other metal structures are required in latent heat thermal storage (LHTS) applications. Previous work has concentrated on numerical and experimental examination in determining the influence of the fins in melting phase change material. This paper presents a simplified analytical model based on a quasi-linear, transient, thin-fin equation which predicts the solid-liquid interface location and temperature distribution of the fin in the melting process with a constant imposed end-wall temperature. The analytical results are compared to the numerical results and they show good agreement. Due to the assumptions made in the model, the speed of the solid-liquid interface during the melting process is slightly too slow.     

Thermophysical and heat transfer properties of phase change material candidate for waste heat transportation system

A waste heat transportation system––trans-heat (TH) system––is quite attractive that uses the latent heat of a phase change material (PCM). The purpose of this paper is to study the thermophysical properties of various sugars and sodium acetate trihydrate (SAT) as PCMs for a practical TH system and the heat transfer property between PCM selected and heat transfer oil, by using differential scanning calorimetry (DSC), thermogravimetry-differential thermal analysis (TG-DTA) and a heat storage tube. As a result, erythritol, with a large latent heat of 344 kJ/kg at melting point of 117°C, high decomposition point of 160°C and excellent chemical stability under repeated phase change cycles was found to be the best PCM among them for the practical TH system. In the heat release experiments between liquid erythritol and flowing cold oil, we observed foaming phenomena of encapsulated oil, in which oil droplet was coated by solidification of PCM.     

Moving boundaries due to distributed sources in a slab

Analytical and numerical solutions have been obtained for some moving boundary problems associated with Joule heating and distributed absorption of oxygen in tissues. Several questions have been examined which are concerned with the solutions of classical formulation of sharp melting front model and the classical enthalpy formulation in which solid, liquid and mushy regions are present. Thermal properties and heat sources in the solid and liquid regions have been taken as unequal. The short-time analytical solutions presented here provide useful information. An effective numerical scheme has been proposed which is accurate and simple.     

High-velocity penetration of a melting solid by a slender body

The high-velocity penetration of a melting solid by a thermally insulated slender body is considered. Under certain constraints on the dimensionless melting parameters the flow in the molten layer can be described within the framework of lubrication theory. The local angle of inclination of the body and the surfaces of the molten layer with respect to the velocity is assumed to be small and is taken into account in the linear approximation. The heat flow into the solid is found by simulating the body and the molten layer by means of a segment with distributed heat sources. Within the framework of this simple formulation a closed solution of the problem of the fusion zone around a moving slender body is constructed. The dependence of the shape of the molten layer and the structure of the temperature and longitudinal velocity fields in the layer on the shape of the body and the other governing parameters of the problem is investigated. The results obtained also give a solution of the problem of the melting of a solid rubbing at high velocity against a thermally insulated rough substrate, when the characteristic height of the roughness is of the order of the thickness of the layer and the characteristic length of the order of the contact length.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.6, pp. 43–48, November–December, 1992.     

Metal foam and fin implementation into a triple concentric tube heat exchanger over melting evolution

It is believed that it is going to be a sizeable mismatch between supply and demand when it comes to renewable resources. Lately, researchers are on course to compensate for the unpredictabilityof such resources by the employment of phase change materials (PCMs). Having multiple advantages, PCMs generally suffer from inadequate thermal conductivity which causes prolonged transition procedures. To tackle this issue, this study is fixated on two parameterswhich are linked to fins addition and porous media incorporation in a melting process within a triple concentric tube heat exchanger (TCTHX). The results provided by multiple cases underlined the significance of natural convection in the bare system, although finned and copper-metal-foam cases outshine buoyancy forces by roughly 45% and 97%, respectively. Material is a major determent when it comes to the selection of porous media as Al₂O₃ registered the weakest performance among SiC, Ni and Cu, however, it managed to speed up the process by 75% which still is much higher than the finned system, implying that porous media is of higher priority over fins. The best scenario transpiredwhile fins and copper metal foam were integrated as 26% and 97% soars in efficacy have been obtained compared to individual incorporation of porous media and fins, respectively.     

Contact melting materials with non-linear properties

The effects of nonlinear thermophysical properties on thermal and flow fields of the molten thin layer produced by contact melting are investigated. The molten layer is assumed to be a non-Newtonian fluid which has temperature-dependent viscosity and thermal conductivity. Heat transfer to solid and temperature field in solid with temperature-dependent conductivity are obtained. Choosing the heating surface of parabolic shape significantly reduce calculations, since closed-form solutions are obtained. Closed-form solutions for velocity, temperature, pressure, and thickness of the molten layer, and criterions to indicate the importance of taking into account the effects of nonlinear properties are provided. Received on 10 January 1997     

Heat transfer mechanisms during short-pulse laser heating of two-layer composite thin films

 Using a simple perturbation technique, an analytical investigation is presented for the heat transfer mechanisms during ultrafast laser heating of two-layer composite thin slabs from a microscopic point of view. The composite slab consists of two thin metal films which are in perfect thermal contact. The microscopic parabolic two-step model is adopted to describe the behavior of the composite slab. In the microscopic two-step model, the heating process is modeled by the deposition of radiation energy on electrons, the transport of energy by electrons, and the heating of the material lattice through electron–phonon interactions. The proposed perturbation technique is used when the normalized temperature difference between the solid lattice and the electron gas is relatively a small perturbed quantity. Received on 20 September 2000 / Published online: 29 November 2001