Applicability of Void Fraction Models in Rod Bundle at High Quality Conditions

Void fraction model is of great importance to the sub-channel analysis.However,the applica-bility of the void fraction models in the sub-channel codes COBRA under high void fraction conditions is not sufficiently validated.Based on a literature review,four void fraction models are selected and applied to the COBRA code to calculate the thermal hydraulic parameters in rod bundles.Comparing to the experimental data obtained in a 4×4 rod bundle using water as coolant,the selected void fraction models are assessed by using relative enthalpy rise and relative mass flux in various sub-channels.It was found that the calculated sub-channel parameters with the Dix model and the slip model（with a slip ratio of 1.5） give the best agree-ment with the experiment data.