A nozzle device comprising a nozzle chamber includes a fluid inlet located at a first side of the nozzle chamber which is operative to introduce fluid into the nozzle chamber in an injection direction and a fluid outlet at a second side of the nozzle chamber which is operative to expel fluid from the nozzle chamber. A high frequency wave generator is also located in the nozzle chamber which is oriented and operative to generate high frequency waves in a direction which is substantially parallel to the injection direction, whereby to impart high frequency energy to the fluid in the nozzle chamber.