Performance enhancement of multi-tube latent thermal energy storage system: Optimization of tube shape, placement and shell aspect ratio

In the present study, the thermal performance of a latent heat storage unit (LHSU), employing Rubitherm-RT35 as a phase change material (PCM), was enhanced by optimizing the geometric design parameters of tubes and shell. The considered design parameters included the external geometry of the tubes (tg = circular, Square, triangular), the aspect ratio of the rectangular shell (Ar_s = 4.23, 1, 0.48), and the location of the tubes from the bottom of the shell (t_l = Z_B, 0.5Z_B, Z_min), where Z_B = [(H-Z_min)/4 -0.5D_h] depends on Height of the shell (H), external hydraulic diameter of the tube (D_h), and the minimum cutoff distance from bottom of the shell Z_min = 5 mm. The melting rate of PCM was optimized using the Taguchi method by employing the L9 design table. Taguchi method was particularly selected for its effectiveness in minimizing simulation variability. Numerical computations were conducted using the enthalpy-porosity model, which treats the PCM in the mushy zone as a porous medium and captures the melting interface implicitly. This approach allows the simulation to avoid explicitly tracking the solid-liquid boundary, streamlining the two-phase modeling into a unified framework. The optimization results show that the heated tubes of triangular shape arranged in a shell with Ar_s = 1 and tubes located at the bottommost configuration i.e., t_l = Z_min, maximize the melting performance of PCM. The optimized LHSU configuration showed a 59 % improvement in PCM melting rate compared to the base case, leading to an overall energy storage enhancement of 24 %.