Design and experimental study of low temperature waste heat storage system using phase change materials
Student name: Mr Anirudh Narla
Guide: Dr Som Mondal
Year of completion: 2018
Host Organisation: Centre of Excellence in Thermal Energy Storage, TERI School of Advanced Studies
Supervisor (Host Organisation): Mr Abhinav Bhaskar
Abstract: Low temperature waste heat has a huge potential but is yet to be tapped. There are a lot of existing conventional recovery technologies but when there is a time lag between the availability of heat and its utilisation, thermal energy storage is an effective solution. Due to its high energy density, latent heat storage is advantageous when compared to sensible heat storage.
As a part of this project, various Phase Change Materials (PCMs) and their thermo-physical properties were studied and Erythritol was chosen as the PCM for latent heat storage because of its suitable melting temperature (120 °C) and high enthalpy of fusion (271.4 J/g). HiTech Therm 60 was selected as the heat transfer fluid (HTF) after careful comparison with other HTFs. Shell-and-tube heat exchanger was chosen because of better heat transfer when compared to other types of heat exchangers. A multi tube (9 tubes) shell-and-tube heat exchanger was designed and fabricated by the Centre of Excellence in Thermal Energy Storage, TERI School of Advanced Studies, before the initiation of this project. Locations were finalised for the placement of thermocouples in the shell side of heat exchanger to study the melting profile of PCM (filled into the shell side of heat exchanger). Insulation for the entire system was done with ceramic fibre. Total mass of PCM put into the system is 1.9 kg and the system is designed for a total heat storage capacity of 1.3 MJ. Experiments were run and the melting behaviour of the PCM was studied at an HTF inlet temperature of 140 °C and flow rate of 4.8 litres per minute. It was observed that the melting was incomplete for these HTF input parameters. It was inferred that the two input parameters of HTF, inlet temperature and flow rate, have to be varied to achieve complete melting i.e., complete latent heat storage and sensible heat storage in liquid form. Also, it was observed that the temperature in the lower annulus of heat exchanger was relatively low. It is understood that there is effect of buoyancy and the solid PCM settles at the bottom, taking more time to melt when compared to the PCM in the upper annulus.
Keywords: Latent Heat Storage, Phase Change Material, Erythritol, Heat Transfer Fluid, Shell-and-Tube heat exchanger
