Ebonite Nozzles are used in Vaccum Ejector Systems to convert High Pressure to Kinetic Energy - Velocity.
Ejectors use a High Pressure Motive to compress a Low Pressure Suction such as gas or air to dischare an intermediate pressure creating or Kinetic Energy system. In a nozzel, pressure is generated at upstream of nozzel. Jet of fluid moving faster than fluid within the pipe, emerges from Nozzel. So upstream of the nozzel is high pressure and low velocity and at nozzel discharge low pressure and high velocity is generated. Thus nozzel converts pressure energy to kinetic energy. If we black off the upstream we would see that the air is sucked in from side inlet and discharging from the end of tube providing us a simple divice of pumping air or gases from surrounding(a basic form of ejector). And a diffuser is used to mix both the incoming strems. Once mixed divergent section slows down the mixture further increasing pressure. This feature discharges pressure higher than the suction branch. This makes the ejector compress and boost the pressure of fluid entertained.
This type of system is used in Oil & Gas Industry and also in Water treatment plants.