Effect of bypassing the heat transfer fluid on charging in a latent thermal energy storage unit

Baghaei Oskouei S., BAYER Ö.

JOURNAL OF ENERGY STORAGE, vol.62, 2023 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 62
  • Publication Date: 2023
  • Doi Number: 10.1016/j.est.2023.106959
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Compendex, INSPEC
  • Keywords: Phase change materials, Natural convection, Melting, Energy storage, SOLAR-ENERGY, PHASE-CHANGE, PERFORMANCE, CONVECTION, WIND
  • Middle East Technical University Affiliated: Yes


Horizontal latent thermal energy storage (LTES) systems that use phase change materials (PCMs) are popular and effective methods of alleviating the intermittency of renewable energy sources. The main issue of PCMs is their low thermal conductivity, resulting in long charging times and slow response. In this investigation, a novel method to overcome this issue is proposed by designing bypassing tubes that redirect the flow of heat transfer fluid to the bottom of the horizontal LTES tank, where the melting rate is the slowest. A series of 3D numerical model are performed based on the enthalpy porosity method and validated using experimental data in the literature. Five bypassing tubes at the bottom of the tank are placed such that the reentry point is near the outlet, where the PCM temperatures are the lowest. Three parameters, the lengths, radial distance, and mass flow rate ratio of the bypassing tubes are studied and the effect of each by investigating the evolution of liquid fraction, PCM temperature, and heat transfer fluid outlet temperatures is studied. Additionally, the charging rate, charging efficiency, and the convective heat transfer coefficient are studied. It is established that the radial distance of the bypass tubes is the most effective parameter on charging time, while the mass flow rate ratio is the least important. With the largest value of radial distance and length, a reduction in total melting time of 67% is achieved. With an increase in bypassing mass flow rate, the charging efficiency of the LTES tank increases dramatically even though the melting time does not change significantly.