Turbine diffusers are configured to improve pressure recovery within the turbo machinery. The diffuser both converts the non-uniform flow off the impeller into a uniform velocity profile and converts the dynamic energy of the flow into pressure with minimal losses. With an effective diffuser, the rotor exit static pressure will be less than the discharge value which increases the total/static pressure ratio of the turbine. With this increase in total/static pressure ratio, the total to total pressure ratio is reduced, but the overall turbine efficiency is improved..
Turbine diffusers are configured to improve pressure recovery within the turbo machinery. The diffuser both converts the non-uniform flow off the impeller into a uniform velocity profile and converts the dynamic energy of the flow into pressure with minimal losses. With an effective diffuser, the rotor exit static pressure will be less than the discharge value which increases the total/static pressure ratio of the turbine. With this increase in total/static pressure ratio, the total to total pressure ratio is reduced, but the overall turbine efficiency is improved..
For more information Read the Handbook of turbomachinery (Joseph Sherma, 2003 pg 342-348):
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compressor, diffuser, combustion section and turbine
converging
volute and or diffuser
Draft tube is used to increase the pressure from the low turbine exit pressure to the pressure of the surrounding to which the fluid is rejected.Only reaction turbines require a draft tube as there is low pressure at the exit of the turbine,where as in an impulse turbine the pressure at the inlet and the exit is essentially the same, which is above the pressure to which the fluid is rejected and thus it require no draft tube.
Steam is redirected back into the boiler from the high-pressure turbine for reheating, but the steam from the low-pressure turbine enters into a condenser to become water again.