Abstract 
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This thesis is focused attention on onedimensional models for fast transient flows in a kinematic nonequilibrium. Besides the thermodynamic nonequilibrium, there is another type of nonequilibrium: the kinematic nonequilibrium, or drift between the phases. Such flow models include bubbly gas/liquid flows which are characterized by strong coupling between the phases, due to the rapid interphase transfers of mass, momentum and energy. As a consequence the assumptions that the phase pressures and the phase temperatures are equal at any crosssection appear consistent with experimental observations.
The set of equations includes a momentum equation which has the form of a relaxation law of the drift velocity. This equation is based on a simplified version of the socalled Voinov  Berne equation for the momentum of the gas in a bubbly flow. The ability of the model to predict steady state critical flows is tested first. This is done by means of an analysis of the sensitivity to variations of the main parameters, and also by comparing the results with two sets of original experimental data on airwater critical flows. Finally, the model is tested in transient conditions, modelling the water hammer phenomena.
