A theoretical model of annular upward flow in a vertical annulus gap

This paper presents a separated flow model of annular upward flow in a vertical narrow annular channel with bilateral heating. The theoretical model is based on fundamental conservation principles: the mass, momentum and energy conservation equations of liquid films and the momentum conservation equation of vapor core. Through numerically solving the equations, liquid film thickness, radial velocity and temperature distribution in liquid films, heat transfer coefficient of inner and outer tubes and axial pressure gradient are obtained. The predicted results of heat transfer coefficients and axial pressure gradient are compared with the experimental data and good agreements between them are found.