Role of heating location on the performance of a natural convection driven melting process inside a square shaped thermal energy storage system

[+] Author and Article Information
Ojas Satbhai

Mechanical Engineering, IIT Kharagpur, Kharagpur, India 721302

Subhransu Roy

Mechanical Engineering, IIT Kharagpur, Kharagpur, India 721302

Sudipto Ghosh

Metallurgical & materials engineering, IIT Kharagpur, Kharagpur, India 721302

1Corresponding author.

ASME doi:10.1115/1.4040655 History: Received October 25, 2017; Revised June 03, 2018


Abstract In this work, numerical experiments were performed to compare the heat transfer and thermodynamic performance of melting process inside the square-shaped thermal energy storage system with three different heating configurations: an isothermal heating from left side-wall or bottom-wall or top-wall and with three adiabatic walls. The hot wall is maintained at a temperature higher than the melting temperature of the PCM, while all other walls are perfectly insulated. The transient numerical simulations were performed for melting Gallium, (a low Prandtl number Pr = 0.0216, low Stefan number, Ste = 0.014, PCM with high latent heat to density ratio) at moderate Rayleigh number (Ra\approxeq10^{5}). The transient numerical simulations consist of solving coupled continuity, momentum, and energy equation in the unstructured formulation using the PISO algorithm. In this work, the fixed grid, a source-based enthalpy-porosity approach has been adopted. The heat transfer performance of the melting process was analysed by studying the time evolution of global fluid fraction, Nusselt number at the hot wall, volume averaged normalised flow-kinetic-energy. The thermodynamic performance was analysed by calculating the local volumetric entropy generation rates and absolute entropy generation considering both irreversibilities due to the finite temperature gradient and viscous dissipation. The bottom-heating configuration yielded the maximum Nusselt number but has a slightly higher total change in entropy generation compared to other heating configurations.

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