Int. Journal of Renewable Energy Development 9 (3) 2020: 361-367 Page | © IJRED – ISSN: 2252-4940.All rights reserved 361 Contents list available at IJRED website Int. Journal of Renewable Energy Development (IJRED) Journal homepage: http://ejournal.undip.ac.id/index.php/ijred Melting Behavior of Phase Change Material in a Solar Vertical Thermal Energy Storage with Variable Length Fins added on the Heat Transfer Tube Surfaces Ramalingam Senthil * , Aditya Patel, Rohan Rao, Sahil Ganeriwal Department of Mechanical Engineering, SRM Institute of Science and Technology, Kattankulathur, Chennai, India ABSTRACT. This paper investigates the melting behaviour of phase change material (PCM) in a vertical thermal energy storage system with provision of thin rectangular fins of uniform and variable lengths on the heat transfer tube surfaces. The selected PCM and heat transfer fluid (HTF) are paraffin wax and water, respectively. The HTF is passed through the helically coiled copper tube of 10 mm diameter to melt the PCM. The time required to complete the melting of PCM in the system with fins is found to be five hours, whereas for the system without fins it is five hours and forty minutes, for the same conditions of constant water temperature of about 70°C and flow rate of 0.02 kg/s. HTF tube with fins is observed to be more effective with a 13.33% faster rate of melting when compared to that of the HTF tube without fins. Such a fast charging process will be helpful in storing maximum energy within a short period/duration of time shorter duration in for solar thermal and heat recovery applications during lean production times. ©2020. CBIORE-IJRED. All rights reserved Keywords: Thermal energy storage, solar energy, phase change materials, charging process, heat transfer fluid, energy storage capacity. Article History: Received: 3 rd April 2020; Revised: 15 th June 2020; Accepted: 25 th June 2020; Available online: 26 th June 2020 How to Cite This Article: Senthil, R. (2020) Melting Behavior of Phase Change Material in a Solar Vertical Thermal Energy Storage System with Variable Length Fins added on the Heat Transfer Tube Surfaces. International Journal of Renewable Energy Development, 9(3), 361-367. https://doi.org/10.14710/ijred.2020.29879 1. Introduction Solar energy utilization is one of the fastest-growing and cost-competitive renewable energy resources worldwide. As solar energy is not a continuous energy source and is not available at night time, there is a mismatch between the energy supply and demand. The thermal requirements during the night and early morning necessitated the development of thermal energy storage (TES) for solar energy systems. TES is a type of energy system that uses the concept of both sensible and latent heat to store the captured heat energy from compact solar thermal collectors and waste heat recovery systems, without loss. TES provides the stored heat use fort at a later time for applications like heating and drying. Thermal energy can be stored either as sensible or latent heat. Latent heat storage (LHS) has a higher capacity to store energy per unit volume compared to sensible heat storage due to latent heat of phase change. PCM’s have a low thermal conductivity between 0.1-0.7 W/m-K. The present review of literature focuses on the improvement of the thermal conductivity of PCMs using fins. LHS depends upon the fast absorption and release of latent heat at the same temperature when a storage material goes through a change of phase from solid to liquid during the day and liquid to solid later when the heat is discharged to thermal applications. Phase change * Corresponding author: rsenthilsrm@gmail.com materials (PCMs) are used in LHS. The range of temperature for the transition of paraffin from solid to liquid phase is 50°C–110°C and the range of heat of fusion is found to vary between 180–210 kJ/kg. Paraffin wax is commercially available with different melting ranges and does not involve phase change segregation. The enhancement of the heat transfer to and from the PCM using metallic fins on the heat transfer tube surfaces has been studied by several researchers over the past decades. The thermal performance of LHS was investigated with stainless-steel fins and aluminum fins of different thicknesses inside the tube to increase the heat transfer rate of the PCM (Wang et al. 2019). The use of wavy channels in the PCM was observed to result in a significant improvement of the charging and the discharging mechanism of PCM (Shahsavar et al. 2019). The thermal storage unit was studied by using a multichannel flat tube and rectangular fins; the convective heat transfer coefficient was observed to increase up to 515 W/m 2 K (Chen et al. 2019). The temperature distribution and energy storage in an annular PCM was enhanced by inclusion of fins in the longitudinal and traverse directions in a cylindrical thermal energy storage (Mostafavi et al. 2020). The decreasing fin edge length ratio helped to significantly reduce the melting time, whereas, it had an Research Article