An improved liquid film model to predict the CHF based on the influence of churn flow

• The general assumption of initial entrained fraction is unreasonable.
• The droplets in churn flow show an inevitable effect on downstream annular flow.
• The original liquid film flow model for prediction of CHF was developed.
• The integration process was modified to start from the onset of churn flow.

The critical heat flux (CHF) for boiling crisis is one of the most important parameters in thermal management and safe operation of many engineering systems. Traditionally, the liquid film flow model for “dryout” mechanism shows a good prediction in heated annular two-phase flow. However, a general assumption that the initial entrained fraction at the onset of annular flow shows a lack of reasonable physical interpretation. Since the droplets have great momentum and the length of churn flow is short, the droplets in churn flow show an inevitable effect on the downstream annular flow. To address this, we considered the effect of churn flow and developed the original liquid film flow model in vertical upward flow by suggesting that calculation starts from the onset of churn flow rather than annular flow. The results indicated satisfactory predictions with the experimental data and the developed model provided a better understanding about the effect of flow pattern on the CHF prediction.