菱形腔内相变材料接触熔化分析

对菱形腔内固体相变材料的接触熔化进行了理论分析.建立了菱形腔内接触熔化分析模型,应用Nusselt 液体边界层理论求解接触熔化区熔化液体的流动控制方程,得到了液膜厚度、熔化速度和熔化体积的无量纲解析表达式.对熔化过程中腔体夹角以及熔化温差Ste的影响规律进行了分析,得到了决定固体完全熔化时间的特征参数,为工程应用提供了一定理论参考.     

冰在平板上接触熔化的分析

分析了矩形平板下冰在压力与温差共同作用下产生的熔化过程。利用接触熔化理论求得压力分布、熔化边界层厚度、作用力与熔化速度关系的表达式，进而分析和得到圆形平板下冰熔化的结果，并分别与压力、温差驱动熔化的结果进行了比较，给出一些有益的结论。     

水平椭圆管内相变材料接触熔化的分析

对水平椭圆管内相变材料接触熔化过程进行了研究。根据椭圆作图法测，将其分段圆弧化后，利用Ｎｕｓｓｅｌｔ液体边界层理论，对紧密接触熔化的液体传热与运动进行了分析。求得管内固体熔化速度、熔化率平均Ｎｕｓｓｅｌｔ数。讨论了影响它们的诸因素，所得结果包含了圆管时的结论。     

围绕椭圆柱温差驱动的有限长接触熔化

提出并研究了相变材料围绕水平椭圆柱，在有限长接触时的温差熔化过程。应用边界层理论求得作用力与熔化速度关系式。讨论了压缩比的影响，并与围绕长椭圆柱以及圆柱有限长接触的温差熔化的结果进行了比较，指出有关文献的错误，给出一些有益的结论。     

水平圆管内相变材料接触熔化分析

研究相变材料在水平圆管内的接触熔化过程,考虑了圆管表面与接触熔化固液相界面法向角度的不同,给出新的物理模型,应用边界层理论推导得熔化过程所应该满足的基本方程,用数值方法求得了新的边界层厚度、压力分布、熔化率、熔化结束时间、努谢尔特数,以及熔化、液面高度的变化规律,并进行了分析讨论,与相关文献的解析结果进行了比较。     

冰在平板下接触熔化的分析

分析了矩形平板下冰在压力与温差共同作用下产生的熔化过程。利用接触熔化理论求得压力分布、熔化边界层厚度、作用力与熔化速度关系的表达式,进而分析和得到圆形平板下冰熔化的结果,并分别与压力、温差驱动熔化的结果进行了比较,给出一些有益的结论     

围绕椭圆柱热源的定热流接触熔化研究

对第二类热边界条件下的接触熔化问题进行研究,针对水平椭圆柱热源,建立了定热流接触熔化模型。运用Nusselt液膜理论建立熔化控制方程,通过理论分析,得到了无量纲熔化方程组。对接触熔化速度,熔化液膜厚度和压力分布等参数的变化规律进行讨论,并与温差熔化结果进行比较,研究第二类热边界条件下的接触熔化规律。结果表明:接触熔化速度随热源施加的热流密度呈类线性变化;熔化速度随热源表面压缩系数J的增加而增大,当J=1时椭圆柱热源的熔化结果适用于圆柱热源,当J=0.1时,椭圆柱热源可按平板热源近似。     

二维轴对称几何形状下接触熔化过程的统一分析

引入三个形状因子和一个体积参数之后，对二维轴对称几何形状下的内部和外部接触熔化过程进行了统一的数学分析，得到接触熔化速率的一般表达式并分别与六种典型几何形状下现有的分析结果相对比，对该表达式的正确性进行了验证，此外，对其局限性进行了简要讨论。     

水平圆柱与平板下相变材料接触熔化的基本方程

讨论相变材料围绕水平圆柱与平板下各种形式的接触熔化过程，系统分析了压力与摩擦作用下熔化的基本特生和规律，推得不同驱动条件下接触熔化所应满足与遵循的基本方程，给出了求解这些方程的一般步骤，最后，指出有关文献中的错误。     

倾斜矩形腔内接触熔化的实验和理论分析

对倾斜矩形腔内相变材料紧密接触熔化过程应用努谢尔特边界层理论,求得适合工程的理论解。运用图像技术记录7种不同的倾斜角(0°、15°、30°、45°、60°、75°和90°)矩形腔体内相变材料的熔化过程,熔化过程图像采用图像数字化的方法得到其相应的液相分数与时间的关系。分析结果与实验数据吻合程度良好。     

Analysis of close-contact melting for octadecane and ice inside isothermally heated horizontal rectangular capsule

Close-contact melting characteristics of phase change materials (PCM) inside horizontal rectangular capsules are examined experimentally. The capsules are heated isothermally and three kinds of aspect ratios (H/W = 3, 1 and 1/3) are provided. Octadecane and ice are used, respectively, as PCM. A method of analysis applying Nusselt's liquid film theory to the close-contact melting heat transfer in the rectangular capsule is presented. The analytical results show good agreement with the experimental data. For the melting of ice, it is found that the effect of natural convection resulting from density inversion of water at 4°C becomes significant for large Stefan numbers.     

An analytical solution of the heat transfer process during contact melting of phase change material inside a horizontal elliptical tube

Close-contact melting processes of phase change material (PCM) inside a horizontal elliptical tube are studied. The theoretical formulas of the melting rate, thickness of liquid layer, elapsed time of solid PCM and Nusselt number during the heat melting process are obtained by analyzing. The results include those of contact melting inside a horizontal cylinder. Finally, the influences of elliptical compression coefficient and temperature difference in melting are discussed, and useful conclusions are drawn. © 1998 by John Wiley & Sons, Ltd.     

Thermal performance simulations of a packed bed cool thermal energy storage system using n-tetradecane as phase change material

The objective of this paper is to study the thermal performance of latent cool thermal energy storage system using packed bed containing spherical capsules filled with phase change material during charging and discharging process. According to the energy balance of the phase change material (PCM) and heat transfer fluid (HTF), a mathematical model of packed bed is conducted. n-tetradecane is taken as PCM and aqueous ethylene glycol solution of 40% volumetric concentration is considered as HTF. The temperatures of the PCM and HTF, solid and melt fraction and cool stored and released rate with time are simulated. The effects of the inlet temperature and flow rate of HTF, porosity of packed bed and diameter of capsules on the melting time, solidification time, cool stored and released rate during charging and discharging process are also discussed.     

Study of contact melting inside isothermally heated vertical cylindrical capsules

Close-contact melting processes of phase change material (PCM) inside vertical cylindrical capsule are studied. PCM are heated by the capsule isothermally at the bottom and side. The theoretical formulas of the melting rate and thickness of liquid layer during the heat transfer process are obtained by analysis, which are convenient for engineering predictions. Finally, the factors that affect melting are discussed, and conclusions are drawn.     

Analysis of contact melting of phase change materials inside a heated rectangular capsule

Close-contact melting processes of phase change material (PCM) inside a horizontal rectangular capsule are studied. The PCM is heated by the capsule at constant heat flux at the top and isothermally at the bottom, and the sides are adiabatic. The theoretical formulas of the dimensionless melting rate and the thickness of the liquid layer during the heat transfer process are obtained by analysing, which is convenient for engineering predictions. Finally, the influences on the melting process are discussed, and conclusions are drawn.     

Numerical and experimental study of spherical capsules packed bed latent heat storage system

A numerical model to simulate a storage system composed of spherical capsules filled with PCM placed inside a cylindrical tank fitted with a working fluid circulation system to charge and discharge the storage tank. The simplified transient one-dimensional model is based on dividing the tank into a number of axial layers whose thickness is always equal or larger than a capsule diameter. It is also assumed that the temperature of the working fluid is uniform and equal to the average temperature of the layer. The solidification process inside the spherical capsule is treated by using a conductive one-dimensional phase change model with convective boundary condition on the external surface. The convection present in the liquid phase of the PCM is treated by using an effective heat conduction coefficient in the liquid region of the PCM. The solution of the differential equations is realized by the finite difference approximation and a moving grid inside the spherical capsules. The geometrical and operational parameters of the system are investigated both numerically and experimentally and their influence on the charging and discharging times was investigated.     

An Analytical Technique of Transient Phase-Change Material Melting Calculation for Cylindrical and Tubular Containers

In this study, an analytical model for a class of heat storage that utilizes latent heat of a phase-change material (PCM) is developed. Two basic shell-and-tube configurations are considered, one in which the PCM melts inside the tubes while the heat transfer fluid (HTF) flows in the shell along it, and the other in which HTF flows inside the tubes while PCM melts outside. A system of partial differential equations, which describes heat transfer and melting of the PCM and heat transfer in the HTF, is derived with some simplifying assumptions, while still capturing and preserving the essential features of the processes involved. These equations are solved analytically, yielding the overall heat exchange parameters, like instantaneous heat transfer rate, stored energy, and overall operation time of the system. The present work shows that the use of the proposed analytical technique and its modifications for the practical PCM arrangements is beneficial. Proper application of the model makes it possible to obtain the parameters of a real PCM melting process in the form of algebraic formulas, both for the transient values of variables over time, and for the overall process characteristics. A comparison with the results of numerical calculations of transient melting, made using computational fluid dynamics, confirms the validity of analytical findings and allows to assess the degree of accuracy of the results of our analytical method in various practical cases.     

Numerical study on melt fraction during melting of phase change material inside a sphere

This paper presents a numerical study on the constrained melting of phase change material (PCM) inside a sphere to investigate the effect of various factors on the melt fraction. A mathematical model of melting processes of the PCM inside a sphere is developed. And experiments are conducted to verify the numerical method. On the basis of the model, the effects of the sphere radius, the bath temperature, the PCM thermal conduction coefficient and the spherical shell material on the melt fraction of PCM inside a sphere are discussed. The results show that the PCM inside a sphere melts fast as the sphere radius is small, the bath temperature increases, and the PCM thermal conductivity is high. And the metal shell with high thermal conductivity should be adopted preferentially. The present study provides theoretical guidance for the design and operation of the phase change heat storage unit with sphere containers.     

Second law analysis of latent thermal storage for solar system

A theoretical model has been developed for analysis and optimization of the solar system using phase change material (PCM). The later consists of a solar air heating collector coupled with a cylindrical storage tank which contains spherical capsules filled with a PCM. Energy and exergy analyses are carried out to understand the behavior of the system using single PCM or multiple PCMs. Numerical results show that the performance of the latent thermal storage system can be ameliored by the judicious choice of the melting temperature of the PCM.