TREATMENT OF NUCLEATION AND BUBBLE DYNAMICS IN HIGH HEAT FLUX FILM BOILING Y. Liu and N. Dinh Department of Nuclear Engineering, North Carolina State University Raleigh, NC 27695-7909, USA yliu73@ncsu.edu, ntdinh@ncsu.edu ABSTRACT This paper reports results of a study of nucleate boiling on a thin liquid film at high heat fluxes. A method to identify and characterize active nucleation sites based on processing of heater surface temperature and local cooling/heating rate is developed. This method is applied to a select dataset of infrared thermometry imaging. The nucleation site density data are compared other literature data and correlations. A large variation and significant uncertainty was observed. Besides that, a range of data analysis is performed. The nucleation temperature, nucleation site distribution, nucleation rate, as well as the neighboring nucleation site distance was analyzed. The extracted data are used to benchmark fundamental modeling assumptions used in current treatments of nucleation and bubble dynamics, particularly for their applicability in high heat flux conditions. Attention is paid on stochastic, dynamic behaviors of nucleation. This scoping study also aims to provide suggestions on design of validation experiments and data processing procedures that enable assessment of model form uncertainty in wall boiling models at high heat fluxes. KEYWORDS Nucleate Boiling; Thin Liquid Film; High Heat Flux; Vapor Bubble; Nucleation Sites 1. INTRODUCTION This paper is concerned with state-of-the-arts modeling and simulation capability to predict two-phase flow (TPF) and boiling heat transfer (BHT) processes. The modern capability referred here is based on two-fluid time or space averaged models, ranging from one-dimensional Eulerian-Eulerian formulation, to sub-channel analysis (SCA), and multi-dimensional Computational Multiphase Fluid Dynamics (CMFD) codes [1] [2] [3]. In the two-fluid models conservation equations of mass, momentum and energy are completed by a set of constitutive laws for inter-phase exchanges of mass, momentum, and energy. For example, wall boiling heat transfer models are used to derive closure relationships for mass exchange (evaporation), and energy sources (heat partitioning). Currently, the wall boiling model is based on nucleation parameters including nucleation site density (NSD), bubble departure diameter (BDD), and bubble departure frequency (BDF). It is noted that the SCA and CMFD capabilities are developed and applied for Thermal-Hydraulic analysis in the Consortium for Advanced Simulation of Light Water Reactors (CASL). Previous work including sensitivity/uncertainty study conducted by CASL researchers on nuclear reactor thermal-hydraulics methods identified high sensitivity of the prediction to boiling heat transfer models, particularly to nucleation site density [4] [5]. In fact, it is well established that a physics-based sound understanding of nucleation behavior is essential to modeling and prediction of boiling thermal-hydraulics. However, a 4097 NURETH-16, Chicago, IL, August 30-September 4, 2015 4097 NURETH-16, Chicago, IL, August 30-September 4, 2015