A converging nozzle used in the stator of a high pressure steam turbine expands a steam mass
A converging nozzle used in the stator of a high pressure steam turbine expands a steam mass flow rate of 1.0 kg/s. The nozzle inlet conditions of the steam are T = 500°C and P = 150 bar. The steam at the outlet of the nozzle is at a pressure of 100 bar. Note that for this expansion ratio the nozzle is not chocked. A testing campaign is performed in order to characterize the nozzle performance by measuring the velocity ratio – i.e, the ratio of the actual nozzle discharge velocity over the ideal discharge velocity, the one corresponding to an isentropic process. The measured velocity ratio is 0.95. The nozzle can be considered adiabatic since the exergy wasted as a consequence of thermal losses is negligible if compared to the exergy associated with the steam flowing through the nozzle, also because the turbine casing is properly insulated in order to limit heat transfer to the environment. Being a static component, the nozzle does not convert energy into work, and its only purpose is to accelerate the flow of steam. Calculate the rate of exergy destruction in the nozzle during steady operation. Calculate both the isoentropic and the exergy efficiency of the nozzle, compare them and comment on the results.
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