[en] One of the difficulties concerned with the mathematical modelling of two-phase flow is the complexity of the transfer phenomena at the interface. The present study is concerned with the effect of virtual mass on phase separation during the acceleration of a two-phase mixture. Virtual mass can be regarded as an induced inertia on the dispersed phase which is accelerating relative to the continuous phase. The virtual mass force, which acts on the dispersed phase, is due to the acceleration of one phase relative to the other. In the course of this study, it was found that the virtual mass acceleration should be objective. This implies that it will be invariant under a change of reference frame. An objective form of the virtual mass acceleration was derived. Parameters required in the virtual mass force model were identified and their values were determined for limiting cases. Analyses were performed to determine if single bubble nozzle/diffuser flow would enable one to discriminate between the various virtual mass acceleration models. The result indicates that it is very difficult to get information about the virtual mass effect from such experiments