Development, verification and application of a new model for active nucleation site density in boiling systems

A new model for active nucleation site density in boiling systems has been developed and preliminarily applied in Computational Fluid Dynamics (CFD) simulations of subcooled boiling in a vertical heated tube. The new model is based on a parametric analysis of existing experimental data. It is a function of three variables: wall superheat, pressure, and contact angle; and is applicable in a wide range of pressures: 0.101 MPa-19.8 MPa. A preliminary study of the temperature dependence of the contact angle has been performed during the development process. The new model is intended to improve the predictions of: (i) interfacial area concentration in two-fluid models, and (ii) wall temperature in subcooled boiling simulations. For the active nucleation site density itself, the verification results showed that the values predicted by the newly developed model are in good agreement with various published experimental data. The model also demonstrated improvements of other existing models. The new model was utilized in CFD simulations of subcooled boiling in a vertical heated tube. The predicted void fraction and wall temperature in subcooled boiling flow agree well with the experimental data.