https://orcid.org/0000-0002-6469-350X
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ABSTRACT
Effective thermal energy storage is essential to overcome the intermittent availability of solar energy. A small cylindrical thermal energy storage unit is investigated to provide heat during the early morning for domestic hot water using flat plate solar water heaters. A helically coiled heat transfer tube (HTF) in cylindrical thermal storage is investigated on charging phase-change material (PCM). An acrylic cylindrical container is used to hold the PCM. HTF tube is made up of copper helical coil with and without a conical section at the bottom of the loop. The heat transfer tube at the bottom is formed into a small conical shape at the helical coil’s center. The selected PCM is paraffin wax with a melting temperature of about 60°C. The HTF temperature is maintained at 75°C at a flow rate of 0.5 kg/min to charge the PCM of 1 kg mass. Part of solid PCM at the container’s bottom was observed with a longer duration to melt entirely without a conical section of the HTF tube. The irregular temperature distribution was also observed in PCM, mainly along the vertical direction. Thus, the complete melting was achieved by a conical coiled heat transfer tube at the container’s bottom. The conical coil length of the HTF tube increased the overall length by 10%. The PCMs melting duration with a conical tube at the bottom reduced significantly by 16% and enhanced average storage effectiveness by 13.06% compared to the HTF tube without the conical coil.
Abbrevations: HTF: Heat transfer fluid; LHS: Latent heat storage; PCM: Phase-change material; TES: Thermal energy storage
Nomenclature
| Cpcm | = | Specific heat of PCM [Jg−1K−1] |
| Cpw | = | Specific heat of water [Jg−1K−1] |
| dT | = | Change in temperature [K] |
| ΔTw | = | Difference between HTF inlet and exit temperature [K] |
| H | = | Hight of the PCM container [m] |
| L | = | Phase change enthalpy of PCM [Jg-1] |
| m | = | Mass of PCM [kg] |
| Qi | = | Heat input to the PCM [J] |
| Qst | = | Heat stored in PCM [J] |
| Qmax | = | Maximum heat stored in PCM [J] |
| R | = | Radius of the PCM container [m] |
| Ta | = | Ambient temperature [K] |
| Ti | = | Initial temperature of PCM [K] |
| Tins | = | Local temperature of each thermocouple [K] |
| Tf | = | Final temperature of PCM [K] |
| Tm | = | Melting temperature of PCM [K] |
| Twi | = | HTF inlet temperature [K] |
| Two | = | HTF inlet temperature [K] |
| t | = | Time duration [min] |
| vi | = | Volume of each thermocouple [m3] |
| vt | = | Total control volume [m3] |
| x | = | Position of thermocouples in radial direction |
| y | = | Position of thermocouples in axial direction |
| wt | = | Weight |
Acknowledgments
The authors acknowledge gratefully to the Head of the department, Dean, School of Mechanical Engineering, Director (Engineering and Technology), SRM Institute of Science and Technology, Kattankulathur, Chennai, India for readily providing the research facility.
Disclosure statement
The authors declare that there is no conflict of interest.
Additional information
Notes on contributors
Banumathi Munuswamy Swami Punniakodi
Banumathi Munuswamy Swami Punniakodi completed B.E. Mechanical Engineering from the University of Madras in 2003 and M.Tech. Computer-Aided Design from SRM University in 2015. He is interested in modelling of energy systems and thermal energy storage systems towards sustainable energy development.
Ramalingam Senthil
Ramalingam Senthil obtained B.E. from the University of Madras in 1997 and M.E. from Anna University Chennai in 2000. He received Ph.D. in Solar Energy from SRM University, Chennai, India in 2017. He has two decades of experience in teaching and industrial experience. He is working as Associate Professor at SRM Institute of Science and Technology, Chennai from 2005. He is the author of more than 55 articles in the indexed journals. He is interested in the social concerns towards sustainability. He is a member of ISES, SESI, FIE and ISTE.