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Thermal Modeling of Phase Change Material (PCM) with Nanoparticles and Porous Matrix for Melting and Freezing

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Title: Thermal Modeling of Phase Change Material (PCM) with Nanoparticles and Porous Matrix for Melting and Freezing
Author: Hossain, Rakib
Department: School of Engineering
Program: Engineering
Advisor: Mahmud, Shohel
Abstract: Thermal enhancement of the phase change material (PCM) using nanoparticle and porous medium is studied analytically, numerically and experimentally for melting and freezing processes of the PCM. Copper nanoparticle of 30nm is dispersed into the base PCM of Paraffin Wax to prepare the PCM with nanoparticle (NanoPCM). NanoPCM is poured into the Aluminum solid matrix of 95% porosity to have NanoPCM and porous medium matrix. Copper nanoparticle and Aluminum solid matrix are used as enhancer for thermal conductivity improvement of Paraffin Wax without affecting the effective volume of PCM and other thermophysical properties such as viscosity, latent heat of fusion and melting temperature. Initially, a conduction model is developed for constant temperature boundary condition. The effect of the volume fraction of nanoparticle and porosity of the porous medium are studied for temperature distribution, heat transfer and melt fraction inside the cavity analytically and numerically. A scale analysis is executed to establish simplified relationships between different non-dimensional parameters such as Fourier number, Stefan number, porosity and volume fraction. The model is compared with the exact solution of existing literature for equivalent thermophysical properties of NanoPCM with porous medium and found good agreement between the exact solution and numerical result of this research. The conduction model is modified by incorporating both convection and conduction heat transfer with constant temperature boundary condition from side. Because of the boundary condition from side, convection and conduction both heat transfer are responsible for phase change initially. After the top melts completely, the melting of remaining part occurs mostly due to conduction heat transfer. The model executes scale analysis to estimate the extent of the complete phase change process. The scale analysis results in simplified relationships among different non-dimensional parameters such as Fourier number, Stefan number, Raleigh number, Nusselt number, porosity of the porous medium and volume fraction of nanoparticles. The natural convection melting process of NanoPCM inside the porous medium is solved numerically. The numerical simulation verifies the correctness of the relationships proposed by scale analysis and identifies the effects of nanoparticle volume fraction, time, Rayleigh number, flow field, thermal field and heat transfer process during the melting of NanoPCM inside the thermal energy storage system. A nearly closed form analytical model with conduction heat transfer is developed to satisfy the application of phase change material under constant heat flux input conditions. From the exact solutions of the models, the temperature distribution and movement of the melting interface inside the phase change region are predicted. The model data is compared with experimental data for interface movement rate and temperature profile at one location of the melting interface. An extensive experimental research is carried out to observe the thermal performance of PCM, NanoPCM, PCM with porous medium and NanoPCM with porous medium for conduction and convection heat transfer with constant heat boundary condition from bottom, side and top. The better thermal performance is observed for heating from bottom because of higher influence of convection heat transfer. The heating from side performs better than the heating from top. The heating from top is mostly conduction heat transfer because of insignificant presence of convection heat transfer. The results are compared with the thermal performance of base PCM, NanoPCM and PCM with foam for similar experimental conditions. From the result, the desired thermal enhancement of NanoPCM with porous medium is observed for conduction heat transfer by improving the charging/discharge time along with low temperature rise. This pioneering research with NanoPCM with porous medium may lead to many future researches for replacing the sensible energy storage system with latent heat energy storage system for various transient thermal applications.
Date: 2016-05

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