A Numerical Investigation of Constrained Melting of Nanostructure-Enhanced Phase Change Materials in a Rectangular Cavity Heated From Below

2012 ◽  
Author(s):  
Li-Wu Fan ◽  
Liang Zhang ◽  
Zi-Tao Yu ◽  
Xu Xu ◽  
Ya-Cai Hu ◽  
...  
Keyword(s):  
Natural Convection ◽  
Phase Change ◽  
Thermophysical Properties ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Liquid Fraction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Rectangular Cavity ◽  
Heat Of Fusion

A numerical study of constrained melting of nanostructure-enhanced phase change materials (NEPCM) consisting of eicosane and various loadings of CNTs in a rectangular cavity heated from below was performed. Assuming that the NEPCM are single-phase PCMs with homogeneous thermophysical properties, the problem was solved using a finite volume method based on the enthalpy-porosity scheme for solid-liquid phase change. The effective thermophysical properties of NEPCM were predicted using the mixture models and empirical equation with respect to the loading of CNTs. Three nominal Grashof numbers corresponding to three sizes of the cavity were considered. Evolutions of the constrained melting processes were presented by means of snapshots of the temperature contour at representative time instants. The melting rates and local heat transfer along the heated bottom were compared quantitatively based on the variations of the instantaneous liquid fraction and average Nusselt number over the bottom during melting, respectively. It was shown that at a given size of the cavity, melting was expedited as more CNTs were introduced. The expediting of melting was mainly attributed to the enhanced thermal conductivity and lowering of latent heat of fusion of NEPCM. The inclusion of CNTs, however, increases considerably the viscosity of melted NEPCM, which in turn leads to less significant natural convection effect during melting. As a result, increase of loading of CNTs was shown to lead to two competing effects. The feasibility of NEPCM in melting is justified when the enhanced heat conduction overweighs the suppressed natural convection.

Natural Convection in an Enclosure With Blend of Micro Encapsulated Phase Change Materials

2013 ◽  
Author(s):  
Yasmin Khakpour ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Thermal Expansion ◽  
Natural Convection ◽  
Phase Change ◽  
Latent Heat ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Pure Water ◽  
Operating Conditions ◽  
Effective Density

This numerical study investigates the effect of using a blend of micro-encapsulated phase change materials (MEPCMs) on the heat transfer characteristics of a liquid in a rectangular enclosure driven by natural convection. A comparison has been made between the cases of using single component MEPCM slurry and a blend of two-component MEPCM slurry. The natural convection is generated by the temperature difference between two vertical walls of the enclosure maintained at constant temperatures. Each of the two phase change materials store latent heat at a specific range of temperatures. During phase change of the PCM, the effective density of the slurry varies. This results in thermal expansion and hence a buoyancy driven flow. The effects of MEPCM concentration in the slurry and changes in the operating conditions such as the wall temperatures compared to that of pure water have been studied. The MEPCM latent heat and the increased volumetric thermal expansion coefficient during phase change of the MEPCM play a major role in this heat transfer augmentation.

Effect of Periodicity of Non-Uniform Sinusoidal Side Heating on Natural Convection in an Anisotropic Porous-Enclosure

2011 ◽  
Vol 110-116 ◽  
pp. 1613-1618 ◽  
Author(s):  
S. Kapoor ◽  
P. Bera
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Stream Function ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Porous Enclosure

A comprehensive numerical study on the natural convection in a hydrodynamically anisotropic as well as isotropic porous enclosure is presented, flow is induced by non uniform sinusoidal heating of the right wall of the enclosure. The principal directions of the permeability tensor has been taken oblique to the gravity vector. The spectral Element method has been adopted to solve numerically the governing differential equations by using the vorticity-stream-function approach. The results are presented in terms of stream function, temperature profile and Nusselt number. The result show that the maximum heat transfer takes place at y = 1.5 when N is odd.. Also, increasing media permeability, by changing K* = 1 to K* = 0.2, increases heat transfer rate at below and above right corner of the enclosure. Furthermore, for the all values of N, profiles of local Nusselt number (Nuy) in isotropic as well as anisotropic media are similar, but for even values of N differ slightly at N = 2.. In particular the present analysis shows that, different periodicity (N) of temperature boundary condition has the significant effect on the flow pattern and consequently on the local heat transfer phenomena.

Numerical Study of Heat Transfer Characteristics of Liquid Flow in a Microtube With Blend of Micro Phase Change Materials

2012 ◽  
Author(s):  
Yasmin Khakpour ◽  
Jamal Seyed Yagoobi
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Liquid Flow ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Finite Thickness ◽  
Local Heat Transfer ◽  
Outer Wall ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

This numerical investigation explores the heat transfer characteristics of liquid flow with two-component (blend) micro phase change materials (MPCM) and compares them with those of a single component MPCM slurry. The numerical domain is comprised of an axisymmetric micro-tube in contact with a finite-thickness solid zone and a constant heat flux applied on the solid outer wall. The ultimate objective is to demonstrate the tunability of PCM fluid’s thermal energy properties when the phase transition temperatures of the PCMs are chosen within a range required for a specific application. This is because different pure PCM materials store latent heat at a specific range of temperatures. The MPCM slurry flow does not reach a fully developed condition as long as the MPCM particles experience phase change in the developing region. The local heat transfer coefficient strongly depends on the corresponding location of the melting zone interface.

Numerical Study of Phase Change of PCM in Spherical Cavities

2017 ◽  
Vol 372 ◽  
pp. 21-30 ◽  
Author(s):  
Fábio Faistauer ◽  
Petros Rodrigues ◽  
Rejane de Césaro Oliveski
Keyword(s):  
Phase Change ◽  
Melting Temperature ◽  
Wall Temperature ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Liquid Fraction ◽  
Fluid Dynamic ◽  
Melting Process ◽  
Constant Wall Temperature ◽  
Spherical Cavities

This work presents a numerical study of the phase change process of PCM (Phase Change Materials) stored in spherical cavities. The numerical model is two-dimensional and it is composed by the equations of conservation of mass, momentum, energy and volumetric fraction, which are modeled using the enthalpy-porosity technique. The computational mesh is tetrahedral, with refinements on regions that have large thermic and fluid dynamic gradients. The numeric model was validated with result from literature. It was studied the melting process of PCM RT35, RT 55 and RT 82 in spherical cavity with constant wall temperature. Four diameters of spheres D were used (40, 60, 80 and 100 mm) and three temperature differences ΔT (10, 20 and 30 oC) between the wall temperature and the melting temperature of the PCM. Liquid fraction results from the 36 cases studied are presented. It was observed that the time required to reach a certain liquid fraction increases with the diameter and reduces with the increment of ΔT, being possible to predict the fusion time by knowing the characteristic length of the sphere. The largest percentage reduction of the fusion time was obtained with ΔT = 10 oC – 20 oC for all the D considered. The shortest fusion time was obtained with the largest ΔT combined with the smallest D. It is possible to see the dependence of the liquid fraction results in relation with the PCM properties and the its independence in relation its melting temperature, since all the PCM studied presented equal fusion time for the same ΔT and D.

Investigation of the Heat Transfer Process in a PCM During Melting Phase

2014 ◽  
Author(s):  
Mohammad Bashar ◽  
Kamran Siddiqui
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Thermal Energy ◽  
Transfer Process ◽  
Phase Change Materials ◽  
Waste Heat ◽  
Liquid Fraction ◽  
Local Heat Transfer ◽  
Heat Transfer Process ◽  
Interface Temperature

Thermal energy storage systems are gaining significance due to their potential use to store renewable energy and waste heat. Phase change materials (PCMs) are considered to be an efficient way to store thermal energy. However, the heat transfer process during the phase change is not well understood. We report on an experimental study conducted to investigate the heat transfer process in a PCM during melting phase. A PCM storage system subjected to bottom heating from a horizontal heated cylinder was considered using wax as the PCM. An imaging technique was used to capture the movement of the solid-liquid interface. Temperature was measured at multiple locations to quantify the heat transfer process. The interface was found to move with a relatively uniform velocity throughout the melting process however, the heat transfer rate was significantly enhanced in the melted (liquid) phase. The local heat transfer coefficient was found to decrease with an increase in the liquid fraction.

scholarly journals Modelling and Numerical simulation of Nano-enhanced PV-PCM System for Heat Transfer Augmentation from the Panel

2021 ◽  
Vol 2054 (1) ◽  
pp. 012051
Author(s):  
B Charles Divyateja ◽  
K S Unnikrishnan ◽  
B Rohinikumar
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Liquid Fraction ◽  
Energy Conversion Efficiency ◽  
Solid Particles ◽  
Heat Transfer Augmentation ◽  
Solar Radiation Flux ◽  
Direct Energy

Abstract Phase change materials (PCMs) can effectively cool photovoltaic (PV) panels by the passive cooling technique, thereby enhancing its direct energy conversion efficiency. However, generally, PCMs have low thermal conductivity, and different methods can be employed to improve the heat transfer rate. Cooling techniques based on phase change materials (PCMs) enhanced by nano-sized solid particles are very promising. In this paper, a mathematical model is developed to simulate the performance analysis of PV attached with nano-enhanced PCM (NEPCM) integrated with fins and compare the same with that of pure PCM case. The system is oriented in a horizontal position and subjected to constant solar radiation flux of 1000 W/m 2. The PCM selected is RT25HC, and the nanoparticle used is CuO for the numerical study. The effects of volumetric concentrations (0%, 2%, and 4%) and fin number on the performance of the system are investigated numerically. Results show that adding nanoparticles is more effective in no fin case compared to finned cases. The maximum reduction in average PV temperature of 2.02 °C is obtained for no fin case with the nanoparticles’ volumetric concentration of 4%. Further enhancement in liquid fraction and energy storage in NEPCM is also achieved compared to the pure PCM system.

Study of Natural Convection Melting of Phase Change Material inside a Rectangular Cavity with Non-Uniformly Heated Wall

2021 ◽  
Vol 406 ◽  
pp. 3-11
Author(s):  
Abdelghani Laouer ◽  
Nesrine Boulaktout ◽  
El Hacene Mezaache ◽  
Salah Laouar
Keyword(s):  
Natural Convection ◽  
Liquid Phase ◽  
Rayleigh Number ◽  
Phase Change ◽  
Phase Change Material ◽  
Numerical Study ◽  
Rectangular Cavity ◽  
Heated Wall ◽  
Left Wall ◽  
Change Material

In the present numerical study, the convection diffusion phenomena associated with solid-liquid phase transition processes during phase change material (PCM) melting within a rectangular cavity is studied. The cavity is heated from left wall with a sinusoidal temperature distribution. Initially the enclosure was filled by solid gallium at melting temperature 29.78°C. The enthalpy-based lattice Boltzmann method (LBM) with D2Q9 particle velocity model is used to solve density, velocity and temperature fields. Influence of Rayleigh number ranging from 103 to 4×105 on streamlines, isotherms and liquid fraction is analyzed. The results indicate that natural convection of liquid phase change material (PCM) plays a significant role in the melting heat transfer of PCM. It is found that the rate of the melting increases with the increase in the values of the Rayleigh number.

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