Boussinesq approximation was implemented in NEPTUNE_CFD -particularly developed for forced convection and turbulent flow- to estimate the flow caused by buoyancy force.The simulation proved that the results are in good agreement with experimental results obtained from the literature for natural convection regime. As a conclusion, the simulation results by Neptune_CFD are very reliable and the Boussinesq hypothesis is well-adapted to predict the natural convection for propane while for higher heat flux, the nucleate boiling model has to be taken into consideration.

Nevertheless, NEPTUNE CFD confronts numerical errors and convergence difficulties in nucleate boiling regime. This may be caused by high gas void fraction in those cases with higher heat flux density. Therefore, more efforts are required to identify the factors and to construct a more stable model for biphasic simulation.