课程名称︰热力学 课程性质︰系定必修 课程教师︰苏金佳 开课学院：工学院 开课系所︰机械系 考试日期（年月日）︰98.01.14 考试时限（分钟）：openbook 50min / closebook 1hr 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : openbook部分 (50min) 1. Steam enters a turbine with a pressure of 30 bars, a temperature of 420℃ and a velocity of 150 m/s. Saturated vapor at 100℃ exits with a velocity of 90 m/s. At steady state, the turbine develops work equal 550 kJ per kg of steam flowing through the turbine. Heat transfer between the turbine and its surroundings occurs at an average outer surface temperature of 500K. Determine the rate at which entropy is produced within the turbine,in kJ/kg K. Neglect the change in potential energy between inlet and exit. (15%) 2. An air compressor operating at steady state receives air at P1 = 1 bar and T1 = 22℃. The ratio of the pressure at the exit to that at the inlet is 6. Neglect heat transfer between the compressor and its surroundings, and kinetic and potential energy changes between the inlet and the exit. If the isentropic compressor efficiency is 80%, determine the temperature of the air at the compressor exit. Use the ideal gas model for air. (15%) 3. Two kilograms of water undergo a process from an initial state where the water is saturated vapor at 100℃, the velocity is 30 m/s, and the elevation is 6 m to a final state where the water is saturated liquid at 10℃, the velocity is 26 m/s, and the elevation is 3 m. Determine the change in exergy. (15%) closebook部分 (1hr) 4. Write down the Clausius and Kelvin-Planck statements of the second law of thermodynamics and discuss the equivalence of these two statements. (10%) 5. Will the work requirement of an actual compression process be greater or less than that of an isentropic one for the same initial and final pressures? Explain the result with the help of a T-s diagram. (10%) 6. (a) Schematically draw the T-s and P-v diagrams of Otto cycle and explain the processes of the cycle. (10%) (b) Under the same compression ratio the efficiency of Otto cycle is higher than that of Diesel cycle. Explain the situation with the help of a T-s or h-s diagram. (10%)_ 7. Explain the physical meanings of the following terms: (a) exergy, (b) Joule- Thomson coefficient, and (c) isentropic efficiency. (5% @, 15% total) --

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