A new mechanistic model for post-dryout heat transfer based on two-region approach

• Propose a two-region model for interfacial heat transfer in post-dryout conditions. • Improve droplet evaporation prediction using CFD-fitted vapor temperature profile. • Develop a modified droplet deposition model including vapor velocity profile and drag law. • Achieve accurate post-dryout wall superheating prediction, outperforming existing models. Considering the significant difference in droplet evaporation rates between the near-wall and central regions during post-dryout heat transfer, as well as the limitations of existing mechanistic models in addressing this discrepancy, this paper proposes a two-region model for interfacial heat transfer calculations. The proposed model divides the flow field into a central region and a near-wall region, performing separate calculations for droplet evaporation and droplet interactions in each region. The radial vapor temperature distribution is determined by fitting CFD results, which subsequently provides the near-wall vapor temperature profile necessary for interfacial heat transfer calculations. Additionally, a new droplet deposition model is developed to calculate the mass flow of droplets transferring between the central and near-wall regions. The proposed model is validated against experimental data obtained from Freon R-134a and water experiments. Evaluation results indicate that the model accurately predicts wall superheating and the heat transfer coefficient in the post-dryout region, thereby enhancing the predictive capability of mechanistic post-dryout heat transfer models.