The effects of thermal non-equilibrium and inlet temperature on two-phase flow pressure drop type instabilities in an upflow boiling system

In this paper a theoretical model for the two-phase flow pressure drop type instabilities in an upflow boiling system is presented. The thermal non-equilibrium effect between the two phases is included assuming the enthalpy profile in the subcooled boiling region. The system of differential equations describing the single-phase and boiling regions of the system (drift-flux model) is solved using finite difference method for the steady state characteristics of the system over a wide range of operating conditions. Upon obtaining the steady state characteristics, the dynamic formulation of the pressure drop type oscillation is solved numerically. The modeling results are verified by the experimental findings. The effect of the thermal non-equilibrium on the steady state characteristics, stability boundaries and oscillation periods at different heat inputs and inlet temperatures are presented as being compared with the experimental measurements as well as the results obtained from the thermal equilibrium model.