A combined heat transfer enhancement technique for shell-and-tube latent heat thermal energy storage

The most significant drawback of latent heat thermal energy storage systems is the low thermal conductivity of phase-change materials (PCMs), which significantly slows thermal energy transfer rates. The objective of this research is to introduce the helical-coiled shell-and-tube unit with spiral fins as an energy and exergy efficient, and melting and solidification time reduction design for the PCM-based TES applications. The new design is a combination of the advantages of horizontal and vertical systems by offering helical-coiled shell-and -tube, proper shell-to-tube dimension ratio and the addition of spiral fins in a single configuration. Numerical experiments are conducted to compare PCM melting and solidification times, energy and exergy efficiency during charging, discharging for nine thermal energy storage designs. The results show that the proposed latent heat thermal energy storage unit, significantly reduces PCM melting and solidification times when compared to vertical (60% reduction in melting time; 26% reduction in solidification time) and horizontal (44% reduction in melting time; 21% reduction in solidification time) shell geometries, and achieves the highest overall exergy efficiency, the lowest solidification time, and low melting time. All units with conical shell geometries significantly reduce PCM melting time, while greatly extending total PCM solidification time.