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

•Modeling of super deep thermosyphons in artificial ground freezing.•Development of a novel cold heterogenous boiling model for thermosyphons.•Bubble nucleation site at thermosyphon wall only.•Formation of three unique zones at deep evaporators.•Observation of a dead-zone at large thermosyphon filling ratios due to hydrostatic pressure. 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 thermosyphons in AGF. The CFD model couples a heterogeneous condensation/evaporation mass transfer model inside the thermosyphon with thermosyphon-pool hydrostatic pressure distribution and heat diffusion 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 parameters 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 temperature 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 fundamental understanding of the performance of super-long thermosyphons in AGF.