Nallusamy et al. / J Zhejiang Univ SCIENCE A 2006 7(8):1422-1430 1422 Study on performance of a packed bed latent heat thermal energy storage unit integrated with solar water heating system * NALLUSAMY N. †1 , SAMPATH S. 2 , VELRAJ R. 3 ( 1 Department of Mechanical Engineering, Sri Venkateswara College of Engineering, Chennai 602 105, India) ( 2 Department of Automobile Engineering, Sri Venkateswara College of Engineering, Chennai 602 105, India) ( 3 Institute for Energy Studies, College of Engineering, Guindy, Anna University, Chennai 600 025, India) † E-mail: nalls@svce.ac.in Received Dec. 18, 2005; revision accepted Mar. 10, 2006 Abstract: In thermal systems such as solar thermal and waste heat recovery systems, the available energy supply does not usually coincide in time with the process demand. Hence some form of thermal energy storage (TES) is necessary for the most effective utilization of the energy source. This study deals with the experimental evaluation of thermal performance of a packed bed latent heat TES unit integrated with solar flat plate collector. The TES unit contains paraffin as phase change material (PCM) filled in spherical capsules, which are packed in an insulated cylindrical storage tank. The water used as heat transfer fluid (HTF) to transfer heat from the solar collector to the storage tank also acts as sensible heat storage material. Charging experiments were carried out at varying inlet fluid temperatures to examine the effects of porosity and HTF flow rate on the storage unit performance. The performance parameters such as instantaneous heat stored, cumulative heat stored, charging rate and system efficiency are studied. Discharging experiments were carried out by both continuous and batchwise processes to recover the stored heat, and the results are presented. Key words: Charging, Discharging, Heat transfer fluid (HTF), Latent heat, Phase change material (PCM), Packed bed, Thermal energy storage (TES) doi:10.1631/jzus.2006.A1422 Document code: A CLC number: TK51 INTRODUCTION Efforts of rational and effective energy man- agement, as well as environmental considerations, increase the interest in using renewable energy sources, especially solar energy. Because of discrep- ancy between the energy supply and demand in solar heating applications, a thermal energy storage (TES) device has to be used for the most effective utilization of the energy source. Energy storage combined with solar collectors and photovoltaic systems have been developed over the years for homes and large build- ings. Although these systems provide energy at a higher cost than fossil fuels, the main advantage is their limited impact on the environment and sustain- ability of the energy source. The most commonly used TES methods are sensible heat storage (SHS) and latent heat storage (LHS). Much research work was carried out on SHS materials and systems in the past and the technology for their utilization was also well developed. However SHS systems have the following disadvantages: (1) low heat storage capacity per unit volume of the storage medium and (2) non-isothermal behaviour during heat storage (charging) and heat release (dis- charging) processes. On the other hand, LHS, with solid-liquid phase change, has received considerable attention due to its advantages such as storing a large amount of energy in a small volume, i.e., high storage density and heat charging/discharging at a nearly constant temperature. Journal of Zhejiang University SCIENCE A ISSN 1009-3095 (Print); ISSN 1862-1775 (Online) www.zju.edu.cn/jzus; www.springerlink.com E-mail: jzus@zju.edu.cn * Project supported by Sri Venkateswara college of Engineering, India.