ENERGY 20250624

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ENERGY SYSTEM FOR SUSTAINABLE ENGINEERING EXAM 24.06.2025 First part: Theory (no access to any supporting material) – 1 h Second part: numerical exercise (access to written supporting material) – 1.15h FIRST PART: THEORY QUESTIONS MULTIPLE CHOICE QUESTIONS: 20 points, true or false, correct 1 point, incorrect -0,5 point, missing 0 points In a gas fired steam generator (α = air/fuel ratio): T F A high %O2 in the flue gas means a good efficiency of the boiler The boiler efficiency is higher if the stack temperature increases It is necessary to operate with α equal to stoichiometric The boiler efficiency is higher if the % of CO in the flue gas increases In a 2-pressure level combined cycle, with respect to a single level one: T F It is possible to better cool the gasses coming from the turbine The turbine has the same number of input and output flows It is possible to run the cycle at higher max pressures The ratio (outlet flow rate/inlet flow rate) on the steam turbine is bigger In a wind generator: T F Most plants are using lift type turbines with horizontal axis The power output is proportional to the air temperature The power output is proportional to the square of the area swept by the turbine The typical equivalent operating hours (EOH) are nearly 5000-6000 h/y in the best sites In a geothermal power plant for electricity generation: T F It is exploited the average thermal gradient existing underground Most of the plants are using steam cycles Steam is always dispersed in the atmosphere The typical equivalent operating hours (EOH) are nearly 2000-3000 h/y in the best sites If the net electricity efficiency of a combined cycle power station increases by 1%: T F The fuel consumption must decrease The airflow rate at the gas turbine inlet must increase If the gas…