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-eq uilibrium effect between the two phases is included assuming the enthalpy p rofile in the subcooled boiling region. The system of differential equation s describing the single-phase and boiling regions of the system (drift-flux model) is solved using finite difference method for the steady state chara cteristics of the system over a wide range of operating conditions. Upon ob taining the steady stale characteristics, the dynamic formulation of the pr essure drop type oscillation is solved numerically. The modeling results ar e verified by the experimental findings. The effect of the thermal non-equi librium on the steady state characteristics, stability boundaries and oscil lation periods at different heat inputs and inlet temperatures are presente d as being compared with the experimental measurements as well as the resul ts obtained from the thermal equilibrium model. (C) 2000 Editions scientifi ques et medicates Elsevier SAS.