Development of pressure-based phase change model for CFD modelling of heat pipes

In order to overcome the problem of thermal balance self-adjustment and consider the hydrostatic pressure influence on boiling in CFD modelling of vapor/liquid phase change heat transfer of heat pipes, a pressure-based phase change model is proposed in this work. This model was then employed to develop a CFD model for the wickless heat pipes, or known as thermosyphons, based on VOF method, which was validated by experimental tests of ammonia thermosyphons. The results show that the variations of predicted thermal parameters during start-up are in agreement with experimental results with reasonable accuracy, and the recommended empirical coefficients of vaporization and condensation in pressure-based phase change model are 0.5 s−1 and 1.5 s−1, respectively, due to the simulation errors of thermal parameters at steady state are all within 3.7%. The CFD model has a decent self-adjusting ability for heat input and output of thermosyphons. In addition, the effect of hydrostatic pressure of liquid on boiling behaviors is well predicted with the use of pressure-based phase change model. This work develops a new vapor/liquid phase change model for the CFD modelling of heat pipes, showing a higher rationality and a wider application range comparing to Lee model.