Numerical Simulation of the Effect of the Size of Nanoparticles on the Solidification Process of Nanoparticle-Enhanced Phase Change Materials

2012 ◽  
Author(s):  
Yousef M. F. El Hasadi ◽  
J. M. Khodadadi
Keyword(s):  
Particle Size ◽  
Phase Change ◽  
Phase Change Materials ◽  
Concentration Field ◽  
Solidification Process ◽  
Liquid Interface ◽  
Constitutional Supercooling ◽  
Fluid Mixture ◽  
Solid Liquid Interface ◽  
Solid Liquid

Nanoparticle-enhanced phase change materials (NEPCM) were proposed recently as alternatives to conventional phase change materials due to their enhanced thermophysical properties. In this study, the effect of the size of the nanoparticles on the morphology of the solid-liquid interface and evolving concentration field, during solidification had been reported. The numerical method that was used is based on the one-fluid-mixture model. The model takes into account the thermal as well as the solutal convection effects. A square cavity model was used in the simulation. The NEPCM that was composed of a suspension of copper nanoparticles in water was solidified from the bottom. The nanoparticles size used were 5 nm and 2 nm. The temperature difference between the hot and cold sides was 5 degrees centigrade and the loading of the nanoparticles that have been used in the simulation was 10% by mass. The results obtained from the model were compared with those existing in the literature, and the comparison was satisfactory. The solid-liquid interface for the case of NEPCM with 5 nm particle size was almost planar throughout the solidification process. However, for the case of the NEPCM with particle size of 2 nm, the solid-liquid interface evolved from a planar stable shape to an unstable dendritic shape, as the solidification process proceeded with time. This was attributed to the constitutional supercooling effect. It has been observed that the constitutional supercooling effect is more pronounced as the particle size decreases. Furthermore, the freezing time increases as the particle size decreases.

Numerical Simulation of the Effect of the Size of Suspensions on the Solidification Process of Nanoparticle-Enhanced Phase Change Materials

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Yousef M. F. El Hasadi ◽  
J. M. Khodadadi
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Phase Change ◽  
Phase Change Materials ◽  
Solidification Process ◽  
Liquid Interface ◽  
Local Concentration ◽  
Solutal Convection ◽  
Solid Liquid Interface ◽  
Solid Liquid

Nanostructure-enhanced phase change materials (NePCM) have been widely studied in recent years due to their enhanced thermal conductivity and improved charge/discharge in thermal energy storage applications. In this study, the effect of the size of the nanoparticles on the morphology of the solid–liquid interface and the evolving concentration field during solidification is reported. Combining a one-fluid-mixture approach with the single-domain enthalpy-porosity model for phase change and assuming a linear dependence of the liquidus and solidus temperatures of the mushy zone on the local concentration of the nanoparticles subject to a constant value of the segregation coefficient, thermal-solutal convection as well as the Brownian and thermophoretic effects are taken into account. A square cavity containing a suspension of copper nanoparticles (diameter of 5 and 2 nm) in water was the model NePCM considered. Subject to a 5 °C temperature difference between the hot (top) and cold (bottom) sides and with an initial loading of the nanoparticles equal to 10 wt. % (1.22 vol. %), the colloid was solidified from the bottom. The solid–liquid interface for the case of NePCM with 5 nm particle size was almost planar throughout the solidification process. However, for the case of the NePCM with particle size of 2 nm, the solid–liquid interface evolved from a stable planar shape to an unstable dendritic structure. This transition was attributed to the constitutional supercooling effect, whereby the rejected particles that are pushed away from the interface into the liquid zone form regions of high concentration thus leading to a lower solidus temperature. Moreover, for the smaller particle size of 2 nm, the ensuing solutal convection at the liquid–solid interface due to the concentration gradient is affected by the increased Brownian diffusivity. Due to size-dependent rejection of nanoparticles, the frozen layer that resulted from a dendritic growth contains regions of depleted concentration. Despite the higher thermal conductivity of the colloids, the amount of frozen phase during a fixed time period diminished as the particle size decreased.

scholarly journals Numerical Solution of Heat Transfer Process in PCM Storage Using Tau Method

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
B. Heydari ◽  
F. Talati
Keyword(s):  
Phase Change ◽  
Phase Change Materials ◽  
Numerical Approach ◽  
Heat Transfer Process ◽  
Liquid Interface ◽  
Tau Method ◽  
Two Dimensional ◽  
Interface Location ◽  
Solid Liquid Interface ◽  
Solid Liquid

Thermal energy storage units that utilize phase change materials have been widely employed to balance temporary temperature alternations and store energy in many engineering systems. In the present paper, an operational approach is proposed to the Tau method with standard polynomial bases to simulate the phase change problems in latent heat thermal storage systems, that is, the two-dimensional solidification process in rectangular finned storage with a constant end-wall temperature. In order to illustrate the efficiency and accuracy of the present method, the solid-liquid interface location and the temperature distribution of the fin for three test cases with different geometries are obtained and compared to simplified analytical results in the published literature. The results indicate that using a two-dimensional numerical approach can predict the solid-liquid interface location more accurately than the simplified analytical model in all cases, especially at the corners.

Modeling and Simulation of Phase Change Materials: Application to Building with Low Energy Consumption

2019 ◽  
Vol 297 ◽  
pp. 187-194
Author(s):  
Izzeddine Saouane ◽  
Abla Chaker ◽  
Tarek Messai ◽  
Hichem Farh
Keyword(s):  
Energy Consumption ◽  
Phase Change ◽  
Phase Change Materials ◽  
Heat Storage ◽  
Liquid Interface ◽  
Latent Heat Storage ◽  
Change Behavior ◽  
The One ◽  
Solid Liquid Interface ◽  
Solid Liquid

The use of phase change materials must allow storage / destocking of energy from solar or internal gains. The applications in the case of light constructions will lead to an improvement in the thermal comfort of users and a reduction in energy consumption. The use of phase change materials (PCMs) in the energy-saving walls themselves makes it possible to substitute sensible heat storage for latent heat storage which requires a much lower volume and mass for the same amount of thermal energy. The objective of this work is the study of heat transfer by conduction during a phase change, and aims on the one hand to model and simulate the phase change behavior and on the other hand to approach the mechanism of heat exchange at the solid-liquid interface. The results obtained in 2D show the temporal evolution of the temperature, the position and the speed of the solid-liquid interface.

scholarly journals Numerical Simulation of Solidification of Colloids Inside a Differentially Heated Cavity

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Yousef M. F. EL Hasadi ◽  
J. M. Khodadadi
Keyword(s):  
Solid Phase ◽  
Colloidal Suspension ◽  
Concentration Field ◽  
Liquid Interface ◽  
Thermosolutal Convection ◽  
Alumina Nanoparticles ◽  
Convection Cell ◽  
Fluid Mixture ◽  
Solid Liquid Interface ◽  
Solid Liquid

Development of the solid–liquid interface, distribution of the particle concentration field, as well as the development of thermosolutal convection during solidification of colloidal suspensions in a differentially heated cavity are investigated. The numerical model is based on the one-fluid mixture approach combined with the single-domain enthalpy porosity model for phase change, and it is implemented in fluent software package. The linear dependence of the liquidus and solidus temperatures with the concentration of the nanoparticles was assumed. A colloidal suspension consisting of water and copper or alumina nanoparticles were considered. In the current investigation, the nanoparticle size selected was 5 and 2 nm. The suspension was solidified unidirectionally inside a square differentially heated cavity that was cooled from the left side. It was found that the solid–liquid interface changed its morphology from a planar shape to a dendritic one as the solidification process proceeds in time, due to the constitutional supercooling that resulted from the increased concentration of particles at the solid–liquid interface rejected from the crystalline phase. Initially, the flow consisted of two vortices rotating in opposite directions. However, at later times, only one counter clockwise rotating cell survived. Changing the material of the particle to alumina resulted in crystallized phase with a higher concentration of particles. If it is compared to that of the solid phase resulted from freezing the copper–water colloidal suspension. Decreasing the segregation coefficient destabilizes the solid–liquid interface and increases the intensity of the convection cell with respect to that of the case of no particle rejection. At slow freezing rates, the resulting crystal phase consisted of lower particle content compared to the case of higher freezing rate.

Numerical Simulation of Solidification of Colloidal Suspensions Inside a Differentially-Heated Cavity

2013 ◽  
Author(s):  
Yousef M. F. El Hasadi ◽  
J. M. Khodadadi
Keyword(s):  
Solid Phase ◽  
Colloidal Suspension ◽  
Concentration Field ◽  
Colloidal Suspensions ◽  
Liquid Interface ◽  
Alumina Nanoparticles ◽  
Convection Cell ◽  
Fluid Mixture ◽  
Solid Liquid Interface ◽  
Solid Liquid

Development of the solid-liquid interface, distribution of the particle concentration field, as well as the development of thermo-solutal convection during solidification of colloidal suspensions in a differentially-heated cavity is investigated. The numerical model is based on the one-fluid-mixture approach combined with the single-domain enthalpy-porosity model for phase change. The linear dependence of the liquidus concentration of the nanoparticles was assumed. A colloidal suspension consisting of water and copper, and alumina nanoparticles were considered. In the current investigation, the nanoparticle size selected was 2 nm. The suspension was solidified unidirectionally inside a square differentially-heated cavity that was cooled from the left side. It was found that the solid-liquid interface changed its morphology from a planar shape to a dendritic one as the solidification process proceeds in time, due to the constitutional supercooling that resulted from the increased concentration of particles at the solid-liquid interface rejected from the crystalline phase. Initially, the flow consisted of two vortices rotating in opposite directions. However, at later times only one counter clockwise rotating cell survived. Changing the material of the particle to alumina results in crystallized phase with a higher concentration of particles if it is compared to that of the solid phase resulted from freezing the copper-water colloidal suspension. Decreasing the segregation coefficient destabilize the solid-liquid interface, and increase the intensity of the convection cell with respect to that of the case of no particle rejection. At slow freezing rates, the crystal phase resulted consisted of lower particle content if it is compared to that resulted from higher freezing rate.

Effect of Twin/Tilt on the Growth of Graphite

1984 ◽  
Vol 34 ◽  
Author(s):  
Zhu Peiyue ◽  
Sha Rozeng ◽  
Li Yanxiang
Keyword(s):  
Solidification Process ◽  
Twin Plane ◽  
Liquid Interface ◽  
Tilt Boundary ◽  
Twin Defects ◽  
Solid Liquid Interface ◽  
Graphite Growth ◽  
Solid Liquid

ABSTRACTThe effect of twin/tilt initiated in the process of graphite growth making the graphite curling and change from flake to vermicular and spheroidal is discussed. With the developing of the solidification process,the modifying elements enrich in the front of solid-liquid interface, the amount of twin defects in the graphite increases,its tilt fashion changes and the graphite formed varies from flake to vermicular and spheroidal. The modifying elements promote the formation of twin/tilt. When the modifying elements are insufficient for spheroidizing,the tilt orientation of twins is changeable,and the graphite formed is twisted. When the modifying elements are sufficient enough, the tilt orientation of twins becomes singular, and the graphite formed tends to be round. According to the energy and kinetics consideration of the formation of twin/tilt boundary, it is predicted that the twin plane would firstly adopt (10Tm), especially the (10T2) plane. This result coincides well with the experimental observations. It is proposed that the formation of SG can be divided into two steps: growth of graphite nucleus into spherulite by twin/tilt mechanism and brancing on it in a spiral mode.

scholarly journals Approximate Analytical Solution for One-Dimensional Solidification Problem of a Finite Superheating Phase Change Material Including the Effects of Wall and Thermal Contact Resistances

2012 ◽  
Vol 2012 ◽  
pp. 1-20 ◽  
Author(s):  
Hamid El Qarnia ◽  
Fayssal El Adnani ◽  
El Khadir Lakhal
Keyword(s):  
Analytical Solution ◽  
Phase Change ◽  
Phase Change Material ◽  
Liquid Interface ◽  
Solid Shell ◽  
Interface Position ◽  
Temperature Distributions ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Change Material

This work reports an analytical solution for the solidification of a superheating phase change material (PCM) contained in a rectangular enclosure with a finite height. The analytical solution has been obtained by solving nondimensional energy equations by using the perturbation method for a small perturbation parameter: the Stefan number,ε. This analytical solution, which takes into account the effects of the superheating of PCM, finite height of the enclosure, thickness of the wall, and wall-solid shell interfacial thermal resistances, was expressed in terms of nondimensional temperature distributions of the bottom wall of the enclosure and both PCM phases, and the dimensionless solid-liquid interface position and its dimensionless speed. The developed solution was firstly compared with that existing in the literature for the case of nonsuperheating PCM. The predicted results agreed well with those published in the literature. Next, a parametric study was carried out in order to study the impacts of the dimensionless control parameters on the dimensionless temperature distributions of the wall, the solid shell, and liquid phase of the PCM, as well as the solid-liquid interface position and its dimensionless speed.

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