Electric Power Converter: Rankine Cycle System. The potassium Rankine cycle was selected as a reference design from among the various thermodynamic power conversion cycles due to its high efficiency and the high operating temperatures in this design. The system is composed of a shell and tube type boiler and a similar condenser, a two stage impulse turbine, an electromagnetic pump, and a generator. Pump input power corresponds to 5.4% of the gross power of 1.33 MWe, or 71.8 kWe. Working fluid conditions such as temperature, pressure drop, velocity and flow direction were calculated for each turbine stage in order to size the blades. The design variables of turbine inlet temperature and pressure, vapor superheat, exit temperature and vapor quality were optimized under the existing thermal constraints to obtain minimum systems mass. Turbine efficiency is a function of the pressure ratio Pi/Pe, the turbine inlet temperature, and vapor quality. The pressure ratio was 25. Turbine efficiency was 81% and the mass flow rate was 5.2 kg/s. Fig. 8 shows the variation of thermodynamic efficiency with vapor quality. We fixed the vapor quality at 90% to avoid liquid metal damage to the turbine blades. This resulted in 20.2% enthalpy extraction. The boiler and condenser were designed as conventional shell and tube heat exchangers. Core heat pipes turn liquid potassium into superheated vapor at the exit of the boiler. The temperature drop along the core heat pipe was assumed to be 30 K. The pressure drop between the boiler exit and the turbine inlet was assumed to be 10%. The heat transfer coefficient was calculated from the Nusselt and Reynolds numbers. The Nusselt number, Nu, is given by: where de is the shell equivalent diameter in metres, Re is the Reynolds number and Pr
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