Influence of the Fin Design on the Melting and Solidification Process of NaNO3 in a Thermal Energy Storage System

Abstract

The melting and solidification process of sodium nitrate, which is used as energy storage material, is studied in a vertical arranged energy storage device with two different bimetal finned tube designs (with and without additional lateral fins) for enhancing the heat transfer. The finned tube design consists of a plain steel tube while the material for the longitudinal (axial) fins is aluminum. The investigation analyses the influence of the lateral fins on the charging and discharging process. Three-dimensional transient numerical simulations are performed using the ANSYS Fluent 14.5 software. The results show that, every obstruction given by lateral fins reduces the melting and solidification velocity in direction to the outer shell. Nomenclature  c p Specific heat at constant pressure (J/(kg·K)) H Total enthalpy (J/kg) H s Sensible enthalpy (J/kg) H lat Latent enthalpy for the phase change in a numerical control volume (J/kg) k Thermal conductivity (W/(m·K)) L Latent heat of fusion (J/kg) S Source term (J/(m 3 ·s)) t Time (s) T Temperature (K) v  Velocity (m/s) Greek Letters  Liquid fraction (-) φ Volume ratio (-)  Celsius temperature (°C)  Thermal conductivity (W/(m·K))  Density (kg/m 3)