Stefan number

About: Stefan number is a research topic. Over the lifetime, 482 publications have been published within this topic receiving 32056 citations.

Heat transfer and parametric studies of an encapsulated phase change material based cool thermal energy storage system

Abstract: This work investigates the transient behaviour of a phase change material based cool thermal energy storage (CTES) system comprised of a cylindrical storage tank filled with encapsulated phase change materials (PCMs) in spherical container integrated with an ethylene glycol chiller plant. A simulation program was developed to evaluate the temperature histories of the heat transfer fluid (HTF) and the phase change material at any axial location during the charging period. The results of the model were validated by comparison with experimental results of temperature profiles of HTF and PCM. The model was also used to investigate the effect of porosity, Stanton number, Stefan number and Peclet number on CTES system performance. The results showed that increase in porosity contributes to a higher rate of energy storage. However, for a given geometry and heat transfer coefficient, the mass of PCM charged in the unit decreases as the increase in porosity. The St number as well as the Ste number is also influential in the performance of the unit. The model is a convenient and more suitable method to determine the heat transfer characteristics of CTES system. The results reported are much useful for designing CTES system.

Extinction behaviour for two-dimensional inward-solidification problems

Abstract: The problem of the inward solidification of a two-dimensional region of fluid is considered, it being assumed that the liquid is initially at its fusion temperature and that heat flows by conduction only. The resulting one-phase Stefan problem is reformulated using the Baiocchi transform and is examined using matched asymptotic expansions under the assumption that the Stefan number is large. Analysis on the first time-scale reveals that the liquid-solid free boundary becomes elliptic in shape at times just before complete freezing. However, as with the radially symmetric case considered previously, this analysis leads to an unphysical singularity in the final temperature distribution. A second time-scale therefore needs to be considered, and it is shown that the free boundary retains its shape until another non-uniformity is formed. Finally, a third (exponentially short) time-scale, which also describes the generic extinction behaviour for all Stefan numbers, is needed to resolve the non-uniformity. By matching between the last two time-scales we are able to determine a uniformly valid description of the temperature field and the location of the free boundary at times just before extinction. Recipes for computing the time it takes to completely freeze the body and the location at which the final freezing occurs are also derived.

Experimental study on melting in a rectangular enclosure heated below with discrete heat sources

Abstract: The melting process of n-octadecane in a rectangular cavity with three discrete protruding heat sources on its bottom surface was studied experimentally. It was observed that the experimental process, for the geometric arrangement in this paper, is neither a fixed melting nor a contact melting, but one in which fixed melting and contact melting take place alternatively. The effects of Stefan number, initial subcooling and aspect ratio on the melting process are reported. The larger the Stefan number, the more frequently the contact melting may occur, so does the aspect ratio. The initial subcooling plays a role only in early stage. As the melting process proceeds, its effect on the melting process becomes less.

A computational solution of a phase-change material in the presence of convection under the most generalized boundary condition

Abstract: This article presents a mathematical model describing inward melting process of a phase change material in the presence of convection under the most generalized boundary condition. It is assumed that the material within a container have different geometrical configuration like circular cylinder or sphere. All thermophysical properties of the solid and liquid regions are assumed to be homogeneous. Initially, we convert the mathematical model into an initial value problem in the form of vector matrix representation using a finite difference technique. Two numerical methods; the operational matrix of integration for Bessel functions and finite element Legendre wavelet Galerkin method, are applied to solve the initial value problem. Thus, the obtained results from both methods analyzed for constant (or time depending) temperature or constant (or time depending) heat flux. The whole study is presented in dimensionless form. The effect of Stefan number, Peclet number, Kirpichev number and Biot number on dimensionless temperature profile and dimensionless moving front are illustrated graphically.