Dynamic CFD modeling coupled with heterogeneous boiling for deep two phase closed thermosyphons in artificial ground freezing

Super-long thermosyphons exceeding 100 m are being employed more frequently in artificial ground freezing (AGF) applications. In this study, we develop a fully-conjugate computational-fluid-dynamics (CFD) model to fundamentally analyze the heat extraction capacity and profile of super-long ther-mosyphons in AGF. The CFD model couples a heterogeneous condensation/evaporation mass transfer model inside the thermosyphon with thermosyphon-pool hydrostatic pressure distribution and heat dif-fusion from the ground. The heterogeneous model also considers the kinetic energy required for bubble nucleation and has been validated against experimental studies from the literature. Three main param -eters have been investigated: 1) the filling ratio, 2) the charge pressure inside the thermosyphon, and 3) the wind temperature. The results reveal a no-boiling-zone below 10-25 m of pool surface. Further, the charge pressure significantly affect the start-up of the thermosyphon. Lastly, lower wind tempera-ture extracts more heat from the ground in a qualitatively similar manner (similar heat flux profile along thermosyphon wall) to that of higher wind temperature. Overall, the results of this study provide funda-mental understanding of the performance of super-long thermosyphons in AGF.Crown Copyright (c) 2022 Published by Elsevier Ltd. All rights reserved.