Flow mixing and fluid residence times in a model of a ventricular assist device.

To provide a reliable tool for predicting the flow in a clinical sac-type ventricular assist device (VAD), a simplified model VAD was developed prior to this study for the purpose of experimental validation of computer simulations of the time-varying flow on a moving grid. At selected locations in the flow field, flow patterns, vortex core trajectories and velocities were compared between the numerical and physical models during one full pumping cycle. The computer simulations showed qualitatively very good agreement with the experiment. Quantitatively, the agreement was less favourable. In order to investigate flow mixing and to evaluate fluid residence times in the model VAD a new tool has been developed: the numerical simulations were extended by injecting a scalar into the flow domain. These simulations allow investigation of the flow mixing qualitatively by visualisation and quantification of fluid residence times. Experimental assessment of the numerical results using dye injection proved to be favourable. The numerical results have been extended to include some prediction of pressure which have been compared with experimental measurements.