A BUBBLE-LAYER-BASED MECHANISTIC MODEL FOR THE SATURATED FLOW BOILING IN VERTICAL CHANNELS

Saturated flow boiling contains complex bubble behaviors and interactions such as sliding, lift-off and coalescence. Currently, the prediction of this process mainly depends on numerical simulations combined with bubble-behavior-related submodels, or a combination of one-dimensional empirical correlations without considering bubble dynamics. Meanwhile, the theoretical analysis is still lacking. Therefore, this paper focuses on the development of a mechanistic model for this process which divides the flow field into different regions in the radial direction due to different bubble motions. Then, mass, energy and momentum exchanges between different regions are considered and reflected through a new set of two-dimensional steady-state conservation equations combined with a modified slip ratio correlation. The present model is verified with experimental data of cross-sectional void fraction profiles in vertical channels which shows pretty high accuracy. On this basis, mass flux between different regions in the radial direction, and distributions of several parameters, such as the vapor quality, velocity and mass flow rates in each region along the channel direction are obtained and analyzed. In comparison, the present model can reveal more detailed information than one-dimensional correlations and can provide a simple, fast and stable way to predict the saturated flow boiling process.