Derivation of new mass, momentum, and energy conservation equations for two-phase flows

• We develop generalized conservation equations for two-phase flows.
• We expand on the current six equation model to include additional fluid fields.
• Derivation of a set of governing equations for six fields in two phases is shown.

System codes are used to analyze nuclear reactor systems during steady state and transient operations. These codes are able to predict pressure drop, void fraction distributions and temperature distributions for various coolants, heated flow geometries, and heat configurations. They also include models for various two-phase flow regimes, but extreme flow conditions that involve significant phase change can tax the current code capabilities. Current system codes have mass, momentum, and energy conservation equations for two fields (liquid and vapor), resulting in a model with six conservation equations. Recent developments in limited applications of a few of these codes have added a separate droplet field from the continuous liquid. This is part of a trend toward the inclusion of more fields (and requisite conservation equations) in system codes. The representation of two phase flow phenomena is improved by increasing the number of fields. Conservation equations based on six fields (liquid, vapor, small bubble, large bubble, small droplet and large droplet) are derived in this work.