课程名称︰ 热力学 课程性质︰ 必修 课程教师︰ 王兴华 开课学院： 工学院 开课系所︰ 机械系 考试日期（年月日）︰ 99.11.02 考试时限（分钟）： 180分钟 是否需发放奖励金：是 （如未明确表示，则不予发放） 单选题 1.Consider a river flowing toward a lake at an average velocity of 5 m/s at a rate of 800m3/s at a location 60 m above the lake surface. The power generation potential of the entire river at that location is (a)638 MW (b)236MW (c) 248MW (d)480MW (e)994MW 2.The power required for an 5000kg truck to climb a 600m long uphill with a slope of 30' in 1 min at a constant velocity is (a)196kW (b)245kW (c)392kW (d)491kW (e)530kW 3.A gas is contained in a vertical, frictionless pistion-cylinder. The pistion has a mass of 8kg and a cross-section area of 30cm3. A compresses spring above the pistion exerts a force of 60N on the piston. If the atmospheric pressure is 100kPa, the pressure inside the cylinder is. (a)127kPa (b)152kPa (c)135kPa (d)146kPa (e)120kPa 4.A well-insulated rigid tank contains 80kg of air, and 2-kW baseboard electric resistance heater in the tank is turned in and kept in for 20 min. Then the temperature rise at the end of 20 min is? (a)26.9C (b)31.7C (c)36.7C (d)29.9C (e)41.8C 5,6 An insulated rigid tank is divided into two parts by a partition. Intially, one part contains 7kg of an ideal gas at 800kPa and 50C, and the other part contains 3kg gas at 400kPa and 100C. The partition is now removed, and the final equilibrum temperature of the gas is (a)75C (b)70C (c)80C (d)65C (e)60C and the pressure is (a)601kPa (b)557kPa (c)654kPa (d)490kPa (e)680kPa 7.Air enters an adiabatic turbin steadily at 800kPa and 900K with a velocity of 80m/s and leaves at 100kPa with a velocity of 150 m/s. The inlet area of the turbine is 0.006m2. If the power output of the turbine is 150kW, the exit temperature of the air is (a)737K (b)618K (c)795K (d)762K (e)709K 8,9 A frictionless piston-cylinder device initially contains air at 200kPa and 0.1m3. At this state, a linear spring(F = kx)is touching the pistion but exerts no force on it. The air is now heated to a final state of 0.9m3 and 1000kPa. Then the total work done by the air is (a)480kJ (b)180kJ (c)275kJ (d)150kJ (e)455kJ the work against the spring is (a)225kJ (b)245kJ (c)90kJ (d)140kJ (e)320kJ 10.A piston-cylinder device initially contains 0.05m3 of air at 150kPa and 400K The air is now expanded to a pressure of 100kPa polytropically(pv^n = C) with n is equal to the specific ratio 1.4(called isentropic expansion). The boundary work done during this process is (a)3.89kJ (b)2.05kJ (c)5.39kJ (d)7.19kJ (e)10.1kJ 11.An insulated rigid tank intially contains 50kg saturated liquid water and water vapor at 200C. At this state, 50% of the mass is occupied by liquid water and the rest by vapor. Now an electric resistor placed in the tank is turn on, and the tank is observed to contain saturated water vapor. The temperature is (a)236C (b)211C (c)205C (d)222C (e)284C 12.A mixing chamber that operates at a pressure of 3000 kPa, water flow at inlet A is at 100 C, at inlet B is superheated steam at 500 C, and the mixture leaves the chamber as saturated liquid. The ratio of the mass flow rate of inlets A and B is (1) 3.39 (2) 2.50 (3) 3.73 (4) 3.08 (5) 4.18 13,14 Two tanks are separtated by a partition. Initially Tank A contains 4~kg steam at 1 MPa and 500 C while Tank B containes 2-kg 200 C saturated liquid- vapor mixture with a vapor mass fration of 50%. Now the partition is removed and the two sides are allowed to mix until the equilibrium is established. If the pressure ofthe final state is 400 kPa, the amount of heat loss from the tank is (a) 4000 ld (b) 4700 kJ (c) 5817 kJ (d) 6100 ld (e) 6850 kJ And the quality ofthe mixture is (a) 23.0 % (b) 38.8 % (c) 30.0 % (d) 55.6 % (e) superhated 15. Steam flow steadily through an adiabatic turbine. The inlet conditions of the steam are 15 MPa, 600 C, and the exit conditions are 10 kPa, 95% quality. If the mass flow rate ofthe steam is 15 kg/s, the power output is (a) 2.24 MW (b) 5.59 MW (6) 11.2 MW (d) 16.8 MW (e) 22.4 MW 16. A cylinder contains 2 kg of steam at 400 kPa and 300 C. Now steam is compressed at constant pressure until its temperature rises to 500 C. The work done during this compression process is (a) 325 kJ (13) 94 kJ (6) 134 ki ((1) 187 kJ (6) 207 kJ 17,18. A 1 m3 rigid tank contains saturated refrigerant-134a at 800 kPa. Initially, 20% ofthe volume is occupied by liquid and the rest by vapor. A valve at the top of the tank is now opened, and vapor is withdrawn from the tank. Heat is transferred to refregirant such that the pressure inside the tank remains constant. The valve is closed when 10% of t11e volume is occupied by liquid. The refrigereant left irom the tank is (1) 172 kg (2) 286 kg (3) 229 kg (4) 72 kg (5) 114 kg, and the total heat transfer for this process is (1) 30,473 kJ (2) 15,236 kJ (3) 20,315 kJ (4) 40,630 kJ (5) 48,756 kJ 19. Refrigerant-134a enters an adiabatic compressor at 60 kPa and -10C with a volume flow rate of 0.2 m3/s and leaves at a pressure of 700 kPa. If the power input to the compressor is 30 kW, then the exit refrigerant temperature is (a) 63 C (b) 33 C (c) 51 C (d) 71 C (e) 80 C 20. Refrigerant-l34a is throttled from the saturated liquid state at 1600 kPa to a pressure of 140kPa. Then the final specific volume of the refrigerant is (a) 0.0128 m3/kg (b) 0.021 m3/kg (c) 0.0365 m3/kg (d) 0.0535 m3/kg (e) 0.0723 mg/kg

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