Rotary drill bits having nozzles to enhance recirculation

A rotary drill bit for use in drilling holes in subsurface formations comprising a bit body having a leading face and a gauge region, a plurality of blades formed on the leading face of the bit body and extending outwardly away from the axis of the bit towards the gauge region so as to define a fluid flow channel between the leading edge of each blade and the trailing edge of the adjacent preceding blade, and a plurality of curing elements mounted along the leading edge of each blade, wherein there is provided, in at least one of said channels, a main nozzle which is located and orientated so as to direct at least the majority of fluid emerging therefrom along the leading edge of one blade so as to clean and cool the cutting elements mounted thereon, and a subsidiary nozzle which is located and orientated so as to direct at least the majority of fluid emerging therefrom along the trailing edge of the blade preceding said one blade in a direction substantially opposite to the direction of flow of fluid from the main nozzle, so as to tend to enhance partial recirculation of fluid flow in said flow channel between the blades.