Characteristics of phase-change flow and heat transfer in loop thermosyphon: Three-dimension CFD modeling and experimentation

Two-phase loop thermosyphon (TPLT) shows an oscillation phenomenon since the complex phase-change heat transfer and flow behaviors, decreases the system reliability in practice. A combined three-dimension CFD simulating/experimental investigation was carried out to investigate the phase-change flow inside TPLT. Results of the 3D-CFD model show good agreement with the experiments, with a maximum deviation of 2.86% and 3.98% for temperature distribution and pressure, respectively. In the vertical evaporator heating mode, the filling ratio of 23.3% produced the lowest total thermal resistance of 0.28-0.22K/W since the dominant heat transfer mechanism of phase-change in the loop. With the increasing FR, from 48.0 to 84.1%, the dominant heat transfer mechanism might be transformed to single-phase convection. Thermal performance with the horizontal evaporator heating mode is better than that with the vertical evaporator heating mode since the good flowability at high FR = 84.1%. In the horizontal evaporator heating mode, a bidirectional flow was observed in the loop with the horizontal evaporator even at low FR = 23.3%, which caused pressure fluctuation and reduced thermal performance. But the flow stability could increase by 90% with the auxiliary of a porous media in the horizontal evaporator, indicating that the porous media had a positive effect on avoiding bidirectional flow.