Showing papers on "Stefan number published in 2013"
TL;DR: In this article, heat transfer enhancement technique by using internal and external fins for PCM melting in a triplex tube heat exchanger (TTHX) was investigated numerically.
350 citations
TL;DR: In this article, the effect of dispersing nanoparticles in the base phase change material (PCM) on the melting heat transfer characteristics in the enclosure was examined for the relevant parameters in the following ranges: the mass particle fraction of nanoparticles, ω p ǫ = 0, 5, 10 ¼ ; the Rayleigh number, Ra f Â= 1.71 Ã 1.67 Ã 10 6 −5 ; the Stefan number, Ste f ´= 0.037 Â 0.108; and the subcooling parameter, Sb
153 citations
TL;DR: In this paper, an enthalpy-based lattice Boltzmann method with a double distribution function (DDF) model is implemented to trace phase change front in a cylindrical-horizontal annul.
63 citations
TL;DR: In this article, a thermal energy storage (TES) system with octadecane-coated copper panels arranged in a vertical configuration to promote a self-induced internal natural convection mechanism is presented.
45 citations
TL;DR: In this paper, the impact of the inclusion of a deformation model is firstly addressed to understand what influences the precise melting behavior; it is found that widening of the contact area at the melting front and induced flow motion inside molten phase change material (PCM) improve the heat transfer toward the melting forward.
40 citations
TL;DR: In this article, a one-phase supercooled Stefan problem, with a nonlinear relation between the phase change temperature and front velocity, is analyzed and the results show that for large supercooling the linear model may be highly inaccurate and even qualitatively incorrect.
34 citations
TL;DR: In this paper, numerical analyses were carried out to study laminar heat transfer and friction characteristics of MPCM slurry in a circular tube with twisted tape inserts, and it was found that the MPMCM slurry and twisted tape insert leads to the best performance of convective heat transfer for the bigger apparent specific heat and the intensive swirl flow.
32 citations
TL;DR: In this paper, a lumped parameter model was developed for one-dimensional heat conduction with melting of a phase change material (PCM) slab with volumetric heat generation.
27 citations
TL;DR: In this article, a double population thermal lattice Boltzmann was applied to solve phase change problem with natural convection in an eccentric annulus, and the simulation of melting process from a concentrically and vertically placed inner hot cylinder inside an outer cold cylinder with Prandtl number of 6.2, Stefan number of 1 and Rayleigh number of 105 was carried out quantitatively.
Abstract: In the present study, a double-population thermal lattice Boltzmann was
applied to solve phase change problem with natural convection in an eccentric
annulus. The simulation of melting process from a concentrically and
eccentrically placed inner hot cylinder inside an outer cold cylinder with
Prandtl number of 6.2, Stefan number of 1 and Rayleigh number of 105 was
carried out quantitatively. It was found that the position of the inner
cylinder inside the outer cylinder significantly influence the flow patterns
including the size and shape of two formed vortexes. It is also observed that
the maximum of liquid fractions occurs where the inner cylinder is mounted at
the bottom of outer cylinder.
19 citations
TL;DR: In this paper, aqueous suspensions of graphite were shape stabilized by the addition of collagen and characterized as phase change materials for cold storage with enhanced thermal conductivity, and the response time upon phase change was somewhat longer than predicted by taking into account the values of thermal diffusivity and the estimated value of Stefan number.
10 citations
TL;DR: In this paper, an interfacial tracking method combines advantages of both deforming and fixed grid approaches to solve melting in a discretely heated rectangular enclosure using an algorithm that calculates the energy balance at the solid-liquid interface.
Abstract: Melting in a discretely heated rectangular enclosure is solved using an interfacial tracking method. The interfacial tracking method combines advantages of both deforming and fixed grid approaches. The location of the melting front was obtained by calculating the energy balance at the solid-liquid interface. Through validating the numerical method with experimental results, it was demonstrated that the interfacial tracking method can be used to solve melting in a discretely heated enclosure at high Rayleigh numbers. Effect of Stefan number and geometry of the heaters on the melting process are also investigated.
15 Nov 2013
TL;DR: In this paper, the authors present a numerical solution of the heat transfer and phase change that occurs during the solidification process of a phase change material (PCM) encapsulated in a spherical container.
Abstract: Macro encapsulation techniques have gained considerable attention in latent heat storage systems for solar energy applications in order to improve the overall energy conversion efficiency in solar thermal power plants. However the heat transfer mechanisms that govern the charging and discharging processes at high operating temperatures are still under development and represent an important aspect in the thermal energy storage design process. This study presents a numerical solution of the heat transfer and phase change that occurs during the solidification process of a phase change material (PCM) encapsulated in a spherical container. A transient two-dimensional axisymmetric mathematical model was solved using the control volume discretization approach along with the enthalpy-porosity method to track the melting front. A spherical shell of thickness t, under the gravitational field is completely filled with liquid PCM. For time t>0, a constant temperature boundary condition Tw, which is lower than the phase change temperature of the PCM, is imposed at the outer surface of the shell. A comprehensive analysis is presented in order to assess the role of the capsule size, buoyancy-driven flow in the liquid phase, and shell outer surface temperature on the thermal performance of the system. Results show that with the increase of Stefan number the solidification rate is enhanced. A reduction of 39.25% in total solidification time is predicted when the Stefan number changed from 0.095 to 0.143. Finally a generalized correlation for the solid mass fraction during solidification is obtained based on a combination of Fourier and Stefan numbers and a dimensionless material parameter.Copyright © 2013 by ASME
TL;DR: In this paper, the authors considered the pressure variations along viscous layer thickness into account, and used a fourth-order Runge-Kutta integrating method at each prescribed interval of time.
Abstract: The history of the study of fluid solidification in stagnation flow is limited to a few cases. Among these few studies, only some articles have considered the fluid viscosity and yet pressure variations along the thickness of the viscous layer have not been taken into account and the energy equation has been assumed to be one-dimensional. In this study the solidification of stagnation flows is modeled as an accelerated flat plate moving toward an impinging fluid. The unsteady momentum equations, taking the pressure variations along viscous layer thickness into account, are reduced to ordinary differential equations by the use of proper similarity variables and are solved by using a fourth-order Runge-Kutta integrating method at each prescribed interval of time. In addition, the energy equation is numerically solved at any step for the known velocity and the problem is presented in a two-dimensional Cartesian coordinate. Comparisons of these solutions are made with existing special ranges of past solutions. The fluid temperature distribution, transient velocity component distribution, and, most important of all the rate of solidification or the solidification front are presented for different values of nondimensional Prandtl and Stefan numbers. The results show that an increase of the Prandtl numbers (up to ten times) or an increase of the heat diffusivity ratios (up to two times) causes a decrease of the ultimate frozen thickness by almost half, while the Stefan number has no effect on this thickness and its effect is only on the freezing time.
TL;DR: In this paper, a finite difference approach to a one-dimensional Stefan problem with periodic boundary conditions is studied, and the evolution of the moving boundary and the temperature field are simulated numerically.
Abstract: A finite difference approach to a one-dimensional Stefan problem with
periodic boundary conditions is studied. The evolution of the moving boundary
and the temperature field are simulated numerically, and the effects of the
Stefan number and the periodical boundary condition on the temperature
distribution and the evolution of the moving boundary are analyzed.
TL;DR: In this article, the authors performed a numerical study of two-dimensional solidification of a binary alloy and developed a finite-difference numerical scheme, which was then used to simulate the evolution of an initially planar solidification front.
TL;DR: In this article, the effect of the gap in melting process on the melting rate of two materials has been investigated using the Taylor series expansion of the one-dimensional Stefan problem and the influence of the material properties of the melt rate.
Abstract: There is always a gap in melting process in the contact surfaces of two materials. The gas trapped in the gap can inhibit heat transfer and cause the contact resistance. The purpose of the study was to determine the effect of the gap to the melting rate. Numerical methods applied to the one-dimensional Stefan problem using a Taylor series expansion is used to calculate the melting rate and the influence of the material properties of the melt rate. The result is a greater temperature difference between the inlet temperature (To) to the melting temperature (Tm) caused the melting speed difference Δu will be larger, the smaller of the melting time difference Δt. The greater of Stefan number will cause melting speed difference Δu greater. The small value of latent heat (C) and density (ρ) will cause the small energy requirements for melting causing the Δu a large, otherwise the small value of thermal conductivity (k) will lead to small Δu so that the ratio of the value of k/ρC is the variable values of Δu.
TL;DR: In this paper, a model of one dimensional model of a magma chamber which gradually cools and solidifies after emplacement in the region is used to analyze moving boundary formulation.
Abstract: Moving Boundary Formulation is used to analyze one dimensional model of magma chamber which gradually cools and solidifies after emplacement in the region. Cooling of a layer of pure melt (magma chamber) from above leads to a temperature profile that increases with depth and is thermally unstable. The vigor of convection thus produced, is determined by Rayleigh-Nusselt number based on the finite depth of liquid layer remaining at a particular time and some other parameters like initial heat flow and Stefan number etc. We solve the nonlinear coupled set of differential equations by Runge-Kutta-Fehlberg method and results for different parameters are compared for phase boundary movement.