Artificial Ground Freezing in Cold Climates Using Multiple Closed Single-Phase Thermosyphons: A Natural Convection Approach

This study introduces a novel, energy-efficient method for artificial ground freezing (AGF) in cold regions using passive single-phase thermosyphons filled with antifreeze that operate without external power. Addressing the high costs and environmental impact of conventional AGF techniques, the research evaluates the feasibility and effectiveness of this passive system for soil stabilization. A two-dimensional numerical model was developed to couple natural convection inside vertical closed thermosyphons with conductive heat transfer in the ground, utilizing real design parameters from a prototype in Ottawa, Canada. The model focuses on a single thermosiphon to reduce its computational complexity and was validated against experimental data with a maximum deviation of 8.33%. Results show that optimizing thermosyphon geometry and spacing enhances freezing performance. Decreasing spacing from 2 to 0.5 m lowered underground temperatures at the wellbore zone from approximately - 8 to - 23 degrees C after 60 days. Increasing the cooled length from 1.5 to 4.5 m decreased temperatures by up to 7 degrees C, while increasing the heated length from 1.5 to 4.5 m raised wellbore temperatures by 6 degrees C. Enlarging the pipe diameter by 5 inches decreased the wellbore temperature by 6.5 degrees C for 1 m spacing. The findings confirm that passive thermosyphons can effectively freeze ground without external energy, offering a cost-effective and environmentally friendly AGF solution. This approach provides foundational guidelines for designing and optimizing thermosyphon systems in geotechnical engineering, with potential applications in cold-region construction. Future work should incorporate complex environmental factors and conduct field experiments to refine the model.