Thermal storage performance of latent heat thermal energy storage device with helical fin under realistic working conditions

Latent heat thermal energy storage has garnered increasing interest and development as a significant technique for recovering waste heat. In this research, the latent heat thermal energy storage device with helical fin is proposed and its thermal storage performance is also investigated by numerical simulation. First, assorted helix pitches (400 mm, 200 mm, 100 mm and 50 mm) and fin numbers are taken into account to investigate the thermal storage performance with various fin parameters. Then, four types of nanoparticles (SiC, TiO2, CuO and Al2O3) are dispersed into the phase change material to address the inherent defect of poor thermal conductivity of phase change material. Afterwards, several realistic working circumstances, including four inclination angles (θ = 0°, 30°, 60° and 90°) and eight oscillating inlet temperatures among which the frequencies are 1 Hz, 2.5 Hz, 5 Hz and 10 Hz, and amplitudes are 0.25, 0.5, 1 and 2, are selected to explore the impact on melting process. The results indicate that shortening helix pitch and increasing fin number can accelerate the melting rate, while the selection of these two parameters needs to consider the thermal storage performance and the processing difficulty as a whole. Furthermore, the selection of nano phase change materials needs to balance the relationship between thermal storage rate and capacity. Compared to the complete melting time when the device is placed vertically, the complete melting time is reduced by 14.3% when the device is placed horizontally. Utilizing the oscillating inlet temperature reduces the complete melting time by at least 21.2% compared to using the steady inlet temperature. When the frequency value is increased from 1 to 10, the complete melting time is only reduced by 3.4%. Complete melting time of the amplitude of 2 is 12.9% shorter than that of the amplitude of 0.25.