Numerical study on the cooling characteristics of hybrid thermosyphons: Case study of the Giant Mine, Canada

Abstract

Hybrid thermosyphons have been installed in several permafrost protection applications due to their ability to operate continuously irrespective of seasonal temperature variations. In winter seasons, the thermosyphon operates passively by transferring energy between the ground and cold ambient air; while in warmer/summer seasons, an active refrigeration plant is used as a substitute for colder climate to extract the heat and freeze the ground. This study presents a novel conjugate mathematical model of hybrid thermosyphons based on thermal resistance networks, coupled with transient two-phase artificial ground freezing heat flow based on the enthalpy method. The model is validated against laboratory experimental data from literature and field test data from the Giant Mine in Yellowknife, Canada. Various design and operating parameters are investigated with the aim to maximizing ground heat extraction while minimizing energy consumption. The results indicate that active refrigeration substantially accelerates the formation of the desired frozen ground volume. After a certain time, passive cooling mode can be continuously adopted to reduce the energy consumption of refrigeration plants while maintaining the desired frozen ground thickness. Finally, the model can be used to assist engineers and practitioners to optimize the design of hybrid thermosyphon for permafrost protection or other ground freezing applications.