On the time space averaged momentum equation for dispersed flow

In the field of nuclear safety analysis, the thermal hydraulic behavior is simulated by solving the time space averaged balance equations for two phase flow. Most thermal hydraulic codes have the similar structure of the balance equations. However, since the equations are formulated based on continua, a question arises that they can be valid even for the spatially dispersed phase. In this paper, we discuss the inherent problem of the existing momentum equation, and propose a modified momentum equation