NUMERICAL MODELING OF THERMAL ENERGY STORAGE SYSTEM Selvan Bellan a Jose Gonzalez-Aguilar a Manuel Romero a Muhammad M. Rahman b,c, D. Yogi Goswami b,d Elias K.Stefanakos b,e a IMDEA Energy Institute, Ramon de la Sagra 3, 28935 Móstoles, Spain b Clean Energy Research Center, University of South Florida, Tampa Fl, USA c Department of Mechanical Engineering, University of South Florida, Tampa, Florida, USA d Department of Chemical & Biomedical Engineering, University of South Florida, Tampa, Florida, USA e Department of Electrical Engineering, University of South Florida, Tampa, Florida, USA ABSTRACT Thermal energy storage in the form of latent heat of fusion of phase change material gained considerable attention in solar energy applications since it significantly increases the energy density and reduces the storage tank size compared to the sensible heat storage system. Several numerical and experimental studies have been conducted to enhance the performance of the system. In this study, 2-D continuous solid phase and effective packed bed models are developed to study the behavior and performance of a thermal energy storage system for high temperature applications, which is composed of spherical capsules encapsulated by phase change material (Sodium nitrate) and high temperature synthetic oil (Therminol 66) as heat transfer fluid. Temperature distribution, fluid flow, melting, solidification and thermocline behavior of the system are predicted and the influence of capsule size on the performance of the system is studied. INTRODUCTION One of the main advantages of concentrated solar power (CSP) technology is to store the thermal energy in storage system for later use and increase the energy source availability beyond normal daylight hours. Hence, significant R&D activities are being developed in the field of thermal energy storage (TES) in recent years. Basically, there are three kinds of storage systems; sensible, latent and thermochemical. Among these, latent heat storage provides high storage density compared with sensible storage systems and nearly constant temperature delivery [1]. Several PCMs have been identified as latent storage media for low [2] and high temperature [3] applications and experimental and numerical studies have been conducted to characterize them [4-5]. Various numerical models have been developed in the past few decades to predict the thermal and hydrodynamic behavior and to investigate the performance of the packed bed latent heat thermal energy storage system [e.g. 6-8]. Brief reviews of the work performed on thermocline storage system with PCM capsules have presented [7-8]. The dynamic discharging characteristics of the TES system with coil pipes have studied [9]. These models are generally classified into three major groups: Single phase model, two phase continuous solid phase model and the concentric dispersion model. In single phase model, the PCM phase and the fluid phase are treated as a single phase whereas in two phase model, the packed bed is represented by two distinct phases. Since detail modeling of each element inside the system is so difficult due to its complex configuration and process dynamics, many hypotheses and correlations have been used in these models. Comparing the utilization of these three models, the continuous solid phase model is more convenient than the concentric dispersion model and more accurate than the single phase model, so, it has been extensively used to study the thermal performance of the packed bed systems [10]. To improve the accuracy of the model, an effective model has been developed and reported recently [10], which is different from the previous models. In this model, the fluid flow through the void among the PCM spheres and the thermal gradient inside the capsules can be investigated. This model doesn’t involve any experimental correlations or empirical expressions except the treatment of the effective thermal 1 Copyright © 2014 by ASME Proceedings of the ASME 2014 8th International Conference on Energy Sustainability ES2014 June 30-July 2, 2014, Boston, Massachusetts, USA ES2014-6382 Downloaded From: http://proceedings.asmedigitalcollection.asme.org/ on 10/15/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use