Some limitations on the use of the assumption of thermal equilibrium between phases: a comparison between theory and experiments on simple water filled systems

Calculations based on the alternative assumptions of equal or unequal phase temperatures are compared with measurements from depressurization experiments on two geometrically simple systems. Water conditions approximated to those in typical water cooled reactors. In general, a thermal non-equilibrium model was required to get agreement with the early transient conditions, when local void fractions were close to zero. But the simple equilibrium assumption proved to be adequate for the longer term calculation of pressure history, however, the transient two-phase frictional losses appear to be underestimated. (author)