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Politecnico di Milano Department of Energy - School of Industrial Engineering Course Energy Systems LM prof. S. Consonni, E. Martelli, M. Romano - Academic Year 2014/15 Written Exam – Energy systems LM pag. 1 di 4 Written Exam 09-Feb-2015 Time: 2.00 h PLEASE NOTICE 1) Exam is open book, but computers and cell phones are NOT allowed. Talking with colleagues and/or copying will lead to the immediate invalidation of the exam. 2) Answer clearly ONLY to the questions posed by the problem sets. Even if correct, additional considerations and/or calculations will NOT be considered. 3) Fill this sheet with your name and return it together with your solutions. 4) MARK EACH SHEET of the solution with YOUR NAME AND PAGE/SHEET NUMBER. 5) The final grade is the sum of the points assigned to the solution of each problem plus a bonus of max 4 points. The bonus will be given based on whether the solution of each problem is complete, as well as on the clarity of the handwriting and the details of the explanations given in the solutions. WRITING AND SHEET/PAGE SEQUENCE MUST BE LEFT TO RIGHT AS USED IN WESTERN COUNTRIES. Admission to the oral test requires a grade of at least 16/30. 6) A grade of 8/30 or lower prevents the possibility to take further written tests in the current exam session. FIRST NAME………………………......……FAMILY NAME……………………………….. Problem 1 (14 points) A boiler burns 2000 kW of natural gas (LHV basis) with an excess air ratio of 30%. The natural gas composition is detailed below: − molar composition: CH4 = 0.910, C2H6: = 0.055, CO2: = 0.010: N2 = 0.025 − molar mass: 17.35 kg/kmol − lower heating value: 46.48 MJ/kg Knowing that: − The thermal efficiency of the boiler is equal to 92%. − The ambient temperature is -35 °C − The air molar composition (see Table below) AIR Mol.…