A bubble transport equation, based on the theory of bubble nucleation and growth, is applied for the analysis of two-phase flashing flows. Spontaneous nucleation at the flashing inception point and heterogeneous nucleation in the liquid bulk are used as boundary and initial conditions, respectively. Analytical solution of the transport equation yields a constitutive relation for the net vapor generation rate along the tube, which is required for closure of a two-fluid set of conservation and balance equations. Model predictions, in terms of flow rates and void fraction distributions, compare favorably with measured data. A mechanistic representation of the thermodynamic and transport conditions at the flashing inception point is described. (C) 2000 Elsevier Science Ltd. All rights reserved.