Thermal behavior of composite phase change material of polyethylene in a shell and coil-based thermal energy storage: Numerical analysis

Energy management and environmental sustainability are important concerns across the world at present. In that context, using recycled waste material such as polyethylene as a phase change material (PCM) in a latent heat storage (LHS) system fulfils both motives. However, effective energy conversion requires proper design of thermal energy storage (TES) and improvement of thermophysical properties of the working material. In the present numerical analysis, a shell and coil-based TES is considered with linear low-density polyethylene (LLDP) as base material to be compounded with functionalized graphene in three different concentrations such as 1 %, 3 %, and 5 %, called composite phase change material i.e., CPCM1, CPCM2, and CPCM3 respectively. The diameter ratio between the coil and shell of TES, termed the geometrical ratio (Gr) is taken as 0.3, 0.5, and 0.7 in the analysis, whereas the coil's pitch length (pc) is varied from 10 mm to 30 mm. The orientation of TES is also varied from horizontal (0 degrees) to vertical position (90 degrees) with an interval of 30 degrees inclination. Results reveal that the charging time for the complete liquefaction of storage material decreases a maximum of 65 % in the case of CPCM 3 with 5 % graphene. Increasing the heat supply from 125 W to 250 W sharply decreases the charging time, however, further increasing heat power affects moderately. The charging time gradually decreases to 56 % and 54 % in the case of LLDP and CPCM 2 respectively as Gr increases from 0.3 to 0.7 in both cases. The pitch length effect on the thermal performance of TES is found to be negligible. The analysis shows that the horizontal position of TES accrues the lowest charging time for the thorough melting of PCM.