In an impulse turbine, where does the steam lose pressure and gain velocity?

In an impulse turbine, the steam loses pressure and gains velocity primarily in the expansion nozzle. The design of the expansion nozzle is crucial, as it transforms the high-pressure steam into a high-velocity jet. When steam passes through this nozzle, its pressure decreases due to the conversion of pressure energy into kinetic energy, resulting in an increase in steam velocity. This high-speed jet of steam then strikes the blades of the turbine rotor, causing it to rotate and convert the kinetic energy of the steam into mechanical energy.

The other options, while relevant components in the steam cycle, do not serve the same purpose in the context of pressure loss and velocity gain. The rotor, for instance, is where the energy conversion occurs but does not affect the pressure and velocity of the steam; the condenser's function is to condense steam back into water and maintain system pressure; the cooling chamber relates to temperature regulation rather than the direct dynamics of the steam's pressure and velocity changes. Thus, the expansion nozzle is distinctively essential for the initial transformation of steam characteristics essential for the operation of the impulse turbine.