The flow is studied in liq-liq extraction etc.
Co-Current and Counter current flow is generally used in heat and mass transfer. In heat transfer,
Co-current means both the hot and cold fluid flow in the same direction and for the counter flow vice versa. Counter current is mostly used in industrial applications. Remember, this should be used only in case of 1-1 shell and tube heat exchanger ( for 1-2, you have liquid flowing in both directions in the tubes)