ANALYSIS OF CRITICAL AND SUBCRITICAL FLOW BOILING

Low pressure flow boiling has been computer-simulated by means of the Homogeneous Equilibrium Mixture (HEM) and algebraic slip model of two- phase flow using a transient computer code. Numerical difficulties wer e experienced when the two-phase velocity exceeded the HEM model's spe ed of sound at the inception of boiling during the solution procedure. An apparent anomaly experienced was the calculation of pressure under shoots ('kinks') across a two-phase boiling region surrounded by singl e-phase subcooled liquid. It is clearly shown that,the HEM model's spe ed of sound is a critical state for the evaluation of the pressure gra dient. When this speed of sound is not exceeded at the inception of bo iling, numerically stable and accurate results are computed. Some mean s of resolving these apparently fundamental and generic problems are s uggested.