Discharging performances of supercooled CH3COONa·3H2O and Na2S2O3·5H2O in the rounded rectangular unit and parametric analysis

Abstract

Discharging performances of supercooled salt hydrate PCM (phase change material) in the rounded rectangular storage unit are numerically investigated with the developed multiphase model. Comparisons are first made between supercooled Sodium acetate trihydrate (SAT, CH3COONa·3H2O) and Sodium thiosulfate pentahydrate (STP, Na2S2O3·5H2O). Effects of environment temperature for storage (t0), temperature of the working fluid (tf), the area – volume ratio of the unit (A/V) and PCM thermal conductivity are then analyzed. The results showed that STP has 8% less loss of latent heat during the triggering crystallization process whereas lower discharging rate than SAT due to the lower melting point. Decreasing t0 from 14 °C to 6 °C results in 9% more latent heat loss; decreasing tf from 38 °C to 30 °C also shortens the time period for heat release from 4h to 1.8h; higher A/V and k lead to the higher heat transfer rate, for A/V =200 m−1, the discharging time is 4.2h shorter than that for A/V =70 m−1; however, the effect of k is negligible when k is over 1 W m−1 K−1 due to the larger thermal resistance on the side of working fluid. The results provide guidance for design and application of supercooled SAT and STP in rounded rectangular units for energy storage in solar heating systems.