  We analyse the flow organization of turbulent fountains in stratified media
under different conditions, using three-dimensional finite-time Lyapunov
exponents. The dominant Lagrangian coherent structures responsible for the
transport barriers in three different configurations suggest a self-similarity
behaviour. After proposing a criterion for delimiting the boundary surface of
the uprising fountain, we quantify the entrainment and re-entrainment rates
under fully developed flow conditions using the proper coefficients. Finally,
our analysis was applied to the Selective Inverted Sink, a technological
application of turbulent fountains, identifying turbulence as the primary
mechanism favouring the device's efficiency.
