Impact of temperature variations on the melting dynamics of PEG 1000 in vertical and horizontal rectangular enclosures

This study examines the impact of varying initial and heated-side temperatures on the melting dynamics and thermal performance of polyethylene glycol 1000 (PEG 1000), an organic phase change material (PCM) suitable for low-temperature thermal energy storage systems. Despite the widespread application of PCMs, limited research has analyzed the combined effects of geometric orientation and temperature boundary conditions on PCM behavior. Six cases were simulated in vertical and horizontal rectangular enclosures using a two-dimensional transient finite volume method and the enthalpy-porosity model in ANSYS Fluent. Results showed that the horizontal enclosure reduced melting time by 45.6%, from 3420 seconds (vertical) to 1860 seconds. Moreover, a 10°C increase in heated-side temperature led to a rise in total stored energy from 200.43 kJ/kg to 210.78 kJ/kg in the vertical setup, indicating up to a 9% variation from the horizontal setup. However, a 10°C decrease in initial temperature caused a 17.5% increase in melting time in the vertical configuration. The Prandtl (208.70), Rayleigh (3.47 × 10⁸ −7.89 × 10⁸), and Stefan (0.427 to 0.569) numbers confirm a convection-driven melting regime. These results highlight how enclosure orientation and boundary temperatures significantly impact heat transfer and energy storage efficiency, making PEG 1000 a promising candidate for building heating, solar thermal systems, and compact latent heat storage. PEG 1000 melting was studied in vertical and horizontal enclosures via CFD.Horizontal setup cut melting time by 45.6% vs. vertical orientation.Energy storage rose by ~ 9% in horizontal due to better convection.Rayleigh and Prandtl numbers confirm convection-dominated melting.PEG 1000 is promising for low-temperature thermal energy storage. PEG 1000 melting was studied in vertical and horizontal enclosures via CFD. Horizontal setup cut melting time by 45.6% vs. vertical orientation. Energy storage rose by ~ 9% in horizontal due to better convection. Rayleigh and Prandtl numbers confirm convection-dominated melting. PEG 1000 is promising for low-temperature thermal energy storage.