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Abstract
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In this paper, the melting (charging) and solidification (discharging) processes of a Phase Change Material (PCM)
in a helical coiled tube heat exchanger as a thermal energy storage unit are investigated experimentally. During
the charging (discharging) process, hot (cold) water flows through the coil. Paraffin wax is used as a PCM in the
shell. The thermal and exergy performances for three different geometries of the shell (cubic, spherical, and
trapezoidal) and different flow rates (0.6, 3, and 6 L/min) are investigated. Additionally, numerical simulation is
conducted for the spherical thermal energy storage. The obtained results indicate that, at a volumetric flow rate
of 6 L/min, the trapezoidal shell reduces the total melting time by 23.38 % and 10.1 % compared to the cubic and
spherical shells, respectively. In the solidification process, the spherical shell exhibits the highest efficiency,
reducing the total solidification time by 13.79 % and 21.21 % compared to cubic and trapezoidal shells,
respectively. Moreover, in a total cycle (both melting and solidification processes) of the thermal energy storage,
the spherical shell outperforms, reducing the complete cycle time by 13.4 % and 1.19 % compared to the cubic
and trapezoidal shells, respectively. In the all investigated shells, energy, and exergy efficiencies increase with
the higher flow rates, with the most significant improvement observed when increasing the flow rate from 0.6 to
3 L/min.
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