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︰机械工程学系 考试日期（年月日）︰100.11/03 考试时限（分钟）：180分 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : (close book) 1.Consider a river flowing toward a lake at an average velocity of 10m/s at a rate of 1000m3/s at a location 100m above the lake surface. The power generation potential of the entire river at that location is (a)708.6 (b)544.6 (c)432.4 (d)944.8 (e)1031 MW. 2.The power required for a 200-kg car to climg a 400-m-long uphill with a slope of 30。in 20s at a constant velocity is (a)98.1 (b)196.2 (c)294.3 (d)147.2 (e)258.4 kW. Assuming Cv=0.718 and Cp=1.005 kJ/kg.K for air 3,4.A rigid tank is divided into two parts by an insulated partition. Initially, one part contains 4 kg of air at 800kPa and 50 C, and the other part contains 6 kg air at 400 kPa and 100 C. The partition is now removed and the final equilibrium temperature of the gas is 100 C. The heat added in is (a)287 (b)180 (c)144 (d)215 (e)251 kJ, and the pressure is (a)663 (b)606 (c)562 (d)517 (e)732 kPa. 5,6.Air is contained in a vertical piston-cylinder assembly by a piston of mass 50 kg and having a face area of 0.01m2. The mass of the air is 4g, and initially the air occupies a volume of 5L (0.005m3). The atmosphere exerts a pressure of 100 kPa on the top of the piston. Heat transfer of 1.5 kJ occurs slowly from the air to the surrounding, and the volume of the air decreases to 2.5 L by a stopper. The change in specific internal energy of the air is (a)-338 (b)-282 (c)-248 (d)-226 (e)-188 kJ/kg. and the final air pressure is (a)141 (b)149 (c)118 (d)49 (e)97 kPa. 7.A rigid tank whose volume is unknow is divided into two parts by a partition. One side of the tand contains air at 527 C. The other side is evacuated and has a volume 1.5 times of size of the part containing the gas. The partition is now removed and the gas expands to fill the entire tand. Heat is now applied to the gas until the pressure equals the initial pressure.The final temperature of the gas is (a)1577 (b)1727 (c)2527 (d)2177 (e)1318 C. 8.An insulated 2-m3 rigid tank contains air at 600 kPa and 350 K. A valve connected to the tank is now opened and air is allowed to escape until the pressure inside drops to 200 kPa.The air temperature during this process is maintained constant by an electric heater place in the tank. The amount of electrical work during this process is (a)400 (b)600 (c)800 (d)1000 (e)1200 kJ. 9.A piston-cylinder device initially contains 0.05m3 of ideal air at 800 kPa and 600 K. The air is now expanded to a pressure of 100kPa polytropically (pv^n =C) with n is equal to the specific ratio 1.2. Determine the (a) boundary work done and (b)geat transfer during this process [Express the solution step by step,详述解题过程] (open book) 11,12.An insulated rigid tank initially contains 10kg saturated liquid water and water vapor at 150 C. At this state, 30% of the mass is occupied by liquid water and the rest by vapor. Now an electric resistor placed in the tank is turned on, and the tank is observed to contain saturated water vapor. The final equlibrium temperature is (a)182 (b)165 (c)157 (d)175 (e)196 C. and the amount of electric work addid in is (a)5799 (b)6213 (c)6430 (d)5567 (e)5907 kJ. 13.Water (3kg) in the frictionless piston-cylinder device is initially at a pressure of 1 Mpa and a quality of 75 %, with the piston seated on a stopper. It takes a pressure of 2 MPa to lift the piston. There is heat transter until the temperature is 500 C. The total heat transferred in the process is (a)4195 (b)3808 (c)3146 (d)4612 (e)5078 kJ. 14.Steam flow steadily through an adiabatic turbine. The inlet conditions of the steam are 10 M:a, 600 C, and the exit conditions are 10 k:a, 90% quality. If the mass flow rate of the steam is 10 kg/s, the power output is (a)5.1 (b)6.4 (c)12.8 (d)10.2 (e)3.8 MW. 15.A mixing chamber that operats at a pressure of 200 kPa, refrigerant-134a flow at inlet A is at -12 C, at inlet B is superheated R-134a at 30 C, and the mixture leaves the chamber as saturated vapor. The ratio of the mass flow rate of inlets A and B is (a)15.7 (b)0.165 (c)0.047 (d)95.8 (e)7.21. 16.Refrigerant-134a is throttled from the saturated liquid state at 600 kPa to a pressure of 140 kPa. The final quality of the refrigerant is (a)20.9 (b)19.2 (c)37.8 (d)25.7 (e)33.4 %. 17,18.An initially evacuated and insulated 1-m3 cylinder is to be charged with refrigerant-134a. A line is connected through a valve with very large capacity contains saturated R-134a vapor at pressure of 1 M:a. At the initial time (t=0), the valve is opened, and R-134a flows into the cylinder, and the valve is immediately shut as the pressure in the cylinder equls that in the refrigerant line. The mass of R-134a that is contained in the cylinder equals that in the refrigerant line. The mass of R-134a that is contained in the cylinder is (a)61.7 (b)52.3 (c)27.9 (d)34.4 (e)43.2 kg. and the temperature of the R-134a in the cylinder is (a)53.8 (b)60.7 (c)66.5 (d)72.5 (e)77.7 C. 19,20.A 1-m3 rigid tank contains saturated refrigerant-134a at 1000kPa. Initially, 20 % of the mass is occupied by liquid. The refrigerant lefe from the tank is (a)14.62 (b)33.53 (c)25.42 (d)6.45 (e)18.88 kg, and the total heat transfer for this process is (a)1103 (b)3229 (c)2500 (d)5733 (e)1898 kJ. Bonus Problem. An insulated tank with an internal volume of 1 m3 initially contains air at 800k:a and 100 C. The leakage of air let the pressure inside slowly drops to 200 kPa, at which point the leakage is found and repaired. The air contains in the tank at the moment is (a)3.12 (b)3.71 (c)1.69 (d)3.95 (e)2.78 kg. --

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