Sensitivity Study of Eulerian Multiphase Boiling Models: Nphase-cmfd

Reliance on multiphase fluid-dynamics models, which are developed with relatively limited experimental data, requires a quantitative assessment of the solution variability due to the approximations. In this paper, uncertainty in the Eulerian multiphase boiling model in the Nphase-CMFD code is assessed in the context of the DEBORA test case and the CRUD problem. The models under consideration are turbulence, wall-boiling heat transfer, bulk flow heat transfer, dispersed phase characterization, and interfacial momentum transfer. Experimental and numerical data are compiled to formulate reasonable ranges for the model parameters of interest. This is done in the context of a larger effort to compare various multiphase codes, including Star-CD and Star-CCM+, and various physical setups. The Nphase-CMFD code was moderately coupled to StarCD in order to meaningfully compare the codes. For parameter ranges based on the available literature, the bubble diameter and turbulent dispersion coefficient were found to have the largest effect on the outputs of interest for the CRUD problem. Although it is well known that the constant bubble diameter in Nphase-CMFD is a poor approximation, the turbulent dispersion coefficient is not usually considered to be important. The results underscore the need for comprehensive uncertainty quantification and further development of some multiphase models.