Experimental investigation of PCM thermal energy storage charge and discharge process with aperiodic (ramp) temperature inputs

Institute of Fluid Flow Machinery, Polish Academy of Sciences, Fiszera 14, PL-80-231 Gdańsk, Poland

^* Corresponding author: jkarwacki@imp.gda.pl

Abstract

In recent years, the use of storages filled with phase-change material (PCM) is increasingly considered. Such design is characterized by a higher density of thermal energy accumulation in comparison with water storages. However, the optimal use of the PCM storages requires a recognition of its dynamic characteristics during the loading and unloading process. This paper presents research aimed at understanding and dynamic description of the heat transfer process in a shell-and-tube thermal energy storage. The experimental test stand and the measurement and control system are described. The investigated storage had a form of a cylindrical tank of 40 dm³ volume in which a coil made of pipes with an external diameter of 3.35 mm was immersed in the PCM. The total heat transfer area was 9.4 m². A lumped parameter model was used to describe mathematically the storage thermal dynamics. The PCM used was commercially available RT15 material with the heat capacity of 150 kJ/kg in the temperature range of 10–17°C. In the investigations, aperiodic (ramp) temperature inputs were used. The storage tests were carried out for low (12 h) and high (6 h) speeds of charging and discharging. The amplitude of the input signal and the liquid temperature at the storage inlet were set to include the phase transition interval of the PCM used. The obtained test results allowed to determine the enthalpy as a function of temperature for the whole storage. The experimental results were also used to validate 0D mathematical model of the heat storage.