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Politecnico di Milano Department of Energy - School of Industrial Engineering Course Energy Systems LM prof. E. Martelli, M. Romano - Academic Year 2016/17 Written Exam – Energy systems LM pag. 1 di 1 Written Exam 27-June-2017 Time: 1.00 h PLEASE NOTICE 1) Books, lecture notes, cell phones are forbidden. Using them or t alking 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, a dditional considerations will NOT be considered. 3) Fill this sheet with your name and return it. 4) Writing and sheet/page sequence must be left to right as used in western countries. FIRST NAME………………………......……FAMILY NAME……………………………….. Question 1 (15 points) Consider the air-cooled condenser of a refrigeration cycle: A) List the main parameters for the design of the condenser. B) Discuss how such parameters affect capital and operating costs and if an optimum value exists. C) Discuss the effect of an increase of the ambient temperature on the refrigeration capacity and the COP of a given refrigeration cycle (i.e. given condenser surface area and given compressor). Question 2 (15 points) A) Write the equation to calculate the stoichiometric oxygen to fuel ratio (both on molar and mass basis), to burn a generic fuel molecule CNCHNHONOSNSNNN. B) Does the the air excess for the combustion in a steam cycle boiler and in a gas turbine combustor differ significantly? Why? C) Give indicative values for the oxygen concentration in the flue gas of a steam cycle boiler and of a gas turbine. D) Explain what type of exergy losses are caused by the air excess in the combustion. Politecnico di Milano Department of Energy School of Industrial and Information Engineering Course Energy Systems…