Numerical Simulation Of Latent Heat Energy Thermal Storage System Based On Fins And Porous Media

The latent heat thermal energy storage(LHTES)systems with solid-liquid phase change materials(PCMs)have been extensively applied to various engineering fields such as energy storage,battery thermal management,electronics cooling due to its small volume change during phase change,large latent heat,and capabilities of maintaining nearly constant temperature.Unfortunately,the low thermal conductivity of PCMs and non-uniformaty of solid-liquid interface induced by gravity hinder the heat transfer rate from LHTES,which leads to slow heat charging rate,considerably long melting time,and seriously depresses their practical applications.To overcome this undesired problem,the techniques developed to improve the heat transfer rate in LHTES include using extended fins,high thermal conductivity porous matrices and nanoparticles.To the present,numerical investigation has been extensively developed for the research on the mechanism of heat transfer and fluid flow in the phase change process.However,there still exsits room for the improvement on simplicity and accuracy of the commonly used numerical methods and the current reseach on melting process are mostly in two dimensions.In addition,it is a challenge to evaluate the thermal performance of each enhancement approaches and compare their effectiveness to each other.The weaknesses of thoes studies hinders people from clearly understanding the heat transfer mechanism of solid-liquid phase change and brings about the challenge to optimize the performance of LHTES.In the first,this paper reveal the essence of the melting process through theoretical analysis.And then we introduce the improved two relaxation time Lattice Boltzmann model for three-dimensional melting problem to trace phase interface and reduce numerical diffusion.Based on the model,we carry out multiple numerical simulations to investigate the convective melting characteristics under different Rayleigh numbers,Prantl numbers and inclination angles of LHTES cavity.It can be found that large Rayleigh numbers and inclination angles have positive effects on accelerating the melting rate.Furthermore,PCM melting in LHTES cavity with different fin configurations has been nmerically invastigated to find out the optimized fin arrangement for enhancing heat transfer performance.The results show that parallel double fins with upper-lower fin length ratio lower than 1 and thin tree shaped fin with long stretch attatched to hot wall have significant impacts on promoting the PCM melting rate,meanwhile the uneven melting caused by natural convection is greatly reduced.At last,fins composed of solid fin and porous fin are installed to PCMs and relative simulations are conducted.One can find that LHTES with this composite fins still has fast melting rate and higher heat storage capacity than solid fin cases.In conclusion,we improve the enthalpy based Lattice Boltzmann model for PCM melting,and also study the heat transfer enchancement under different fin structures and PCM thermophysical parameters.The research results can provide theoretical guidance and data support for the improvement of solid-liquid phase change LHTES system.