Recent advances in nucleate boiling modelling and application to DNB for uniform and nonuniform heat flux

Extensive efforts have been made in the last five decades to evaluate the boiling heat transfer coefficient and the critical heat flux in particular. Boiling crisis remains a major limiting phenomenon for the analysis of operation and safety of both nuclear reactors and conventional thermal power systems. As a consequence, models dedicated to boiling flows have been improved. For example, Reynolds Stress Transport Model, polydispersion and two-phase flow wall law have been recently developed. Nevertheless, these models are still being improved. In a previous work, a new mechanistic model has been implemented in a computational multi-fluid dynamics tool leading to wall temperature excursion and onset of boiling crisis. Even if this model covers a large physics scope in terms of mass flux, pressure, quality and channel diameter, it was necessary to improve the calculation of the critical heat flux in some cases as for high values of quality and low pressure at outlet. As a consequence, the paper aims at presenting the generalization of the previous DNB model and its validation against 1500 validation cases. The main contribution of this paper concerns the application of the DNB model to the DNB calculation of nonuniform heat flux. For results consistency, all computations presented in this paper were performed with the standard version of NEPTUNE_CFD and with a single and consistent set of models. All this work has been done following the existing best practice guidelines and a mesh sensitivity analysis has been carried out for all the validation process.