课程名称︰热力学 课程性质︰机械系大二必修 课程教师︰马小康 开课学院：工学院 开课系所︰机械工程系 考试日期（年月日）︰101/11/13 考试时限（分钟）：60 是否需发放奖励金：是 试题： (25%) (1)Please explain the following terms: (a) Intercooling of pump (b) Carnot heat engine cycle (c) Clausius Statement (d) Two entropy change of ideal gases . (e) What is the definition of s in the following term? ┌ 2 . . │ Cp(T)/T dT = s2 - s1 ┘ 1 (20%) (2) An ideal gas undergoes with constant heat capacities undergoes the reversible cycle. The process making up the cycles are 1-2 is a constant volume process 2-3 is an isothermal process 3-4 is an adiabatic process 4-1 is a constant pressure process (a) Please plot the T-S diagram (b) Calculate the network, W net (15%) (3) It is claimed that the efficiency of a completely reversible heat engine can be doubled by doubling the temperature of the energy resource. Justify the validity of this claim. (20%) (4) A 50-kg iron block and a 20-kg copper block, both initially at 80 C, are dropped into a large lake at 15 C. Thermal equilibrium is established after a while as a result of heat transfer between the blocks and the lake water. Determine the total entropy generate in this process. The specific heats of iron and copper at room temperature are C =0.45kJ/kg.C and C =0.386kJ/kg.C iron copper (20%) (5) It is desired determine the unknown volume of the tank(Tank B) in a operating process. It is not possible either to measure directly the volume of the tank or to weigh its contents. However, tank B may be evacuated and then connected to a second tank (Tank A) of known volume which contains steam at known P and T. (The lines and valve connecting the two tanks are assumed to have negligible volume and to be perfectly insulated.) Assumption: The steam in a 1 m3 tank (x=0.6) is released from 400kPa until the pressure in the tank A reduces to 200kPa. Please determine the mass withdrawn from tank A and the unknown volume of a tank B. --

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