Numerical simulation of the heat transfer characteristics of a U-shaped thermosyphon containing a PCM suspension

Abstract The present study investigates the heat transfer characteristics of a U-shaped vertical closed-loop thermosyphon filled with a phase change material (PCM) suspension using numerical simulation. The loop is made of a copper pipe (outer diameter/inner diameter = 1.46). The heating section and the cooling section are located at the bottom and top of the loop, respectively, and octadecane is used as the PCM. Parametric simulations were conducted using the pertinent physical parameters of a loop with a fixed geometrical configuration with the following parameter ranges: modified Rayleigh number Ra ∗ = 5 × 10 3 - 5 × 10 5 , modified Stefan number Ste ∗ = 0.05 - 5 , PCM suspension concentration f p  = 0–10%, PCM particle dimensionless diameter D p  = 0.23–0.0023, and modified subcooling factor S c ∗ = 0.2 - 1.0 . The results show that Ste ∗ presents a critical value under the given parametric conditions; when Ste ∗ is less than the critical value, the latent heat effect becomes significant, and the temperatures in the heating and adiabatic sections of the loop decrease considerably.