Modeling and evaporator design of a separate‐type heat pipe system for seasonal cold thermal energy storage

Seasonal cold thermal energy storage, which stores naturally available winter cold energy for summer cooling, has been proposed as a promising non‐electric technology compared with conventional electrically driven cooling systems. In this study, an enhanced numerical model for a separate‐type heat pipe system is developed, with particular emphasis on the evaporation and condensation heat transfer coefficients governing heat pipe performance. Both coefficients are evaluated based on experimental observations. A visualization experiment is conducted to directly observe ice formation and growth around vertical evaporator pipes with varying diameters, and time‐resolved ice thickness is extracted from recorded images for model validation. The model demonstrates good agreement with experimental results, accurately predicting both the temporal evolution and axial variation of ice thickness. The validated model is further applied to predict ice growth under realistic winter weather conditions using typical meteorological year data for three distinct regions. Design optimization is performed by considering both ice storage capacity and manufacturing cost. It reveals that a climate‐dependent optimal pipe diameter exists and balances thermal performance and cost. The findings of this study provide experimentally validated design guidelines for a separate‐type heat pipe system storing ice in winter.