Chapter 3 PBL3–27 A piston–cylinder device contains 0.85 kg of refrigerant- 134a at 2108C. The piston that is free to move has a mass of 12 kg and a diameter of 25 cm. The local atmospheric pres- sure is 88 kPa. Now, heat is transferred to refrigerant- 134a until the temperature is 158C. Determine (a) the final pressure, (b) the change in the volume of the cylinder, and (c) the change in the enthalpy of the refrigerant-134a. Answer: a) 90.4kPa, b) 0.0205m3, c)17.4kJ/kg 3–36 Water is to be boiled at sea level in a 30-cm-diameter stainless steel pan placed on top of a 3kW electric burner. If 60 percent of the heat generated by the burner is transferred to the water during boiling, determine the rate of evaporation of water. Answer a) 2.872kg/h 3–38 10-kg of R-134a at 300 kPa fills a rigid container whose volume is 14 L. Determine the temperature and total enthalpy in the container. The container is now heated until the pressure is 600 kPa. Determine the temperature and total enthalpy when the heating is completed. Answer: T1=0.61⁰C, T2=21.44⁰C, H1=545.6kJ, H2=846.4kJ 3–40 Water initially at 200 kPa and 300⁰C is contained in a piston-cylinder device fitted with stops. The water is allowed to cool at constant pressure until it exists as a saturated vapor and the piston rests on the stops. Then the water continues to cool until the pressure is 100 kPa. On the T-v diagrams sketch, with respect to the saturation lines, the process curves passing through both the initial, intermediate, and final states of the water. Label the T, P and v values for end states on the process curves. Find the overall change in internal energy between Chapter 3 PBL the initial and final states per unit mass of water. Answer: Δ=1300kJ/kg . Answer: T final=151. Answer: a) T2=1246K. the compressibility charts. Answer: a) V=0.006476m3. (c) Determine the volume change.4-kg saturated liquid water at 200⁰C. One side of the tank contains an ideal gas at 9278C. Answer: T2=3327⁰C 3–78 Determine the specific volume of superheated water vapor at 3. Determine the final temperature of the gas. Answer: a) ʋ=0. c) ΔU=1892kJ 3–71 A rigid tank whose volume is unknown is divided into two parts by a partition.09533m3/kg (3. and (c) the internal energy change of the water. Δ=-0. c) ʋ=0. b) ʋ=0. (b) the final temperature and pressure.14222m3 3–55 A rigid tank initially contains 1. Determine the final temperature using the ideal gas equation of state.7% error).09196m3/kg 3–83 Saturated water vapor at 350⁰C is heated at constant pressure until its volume has doubled. Now heat is supplied to the water until the tank contains saturated vapor only. Heat is now applied to the gas until the pressure equals the initial pressure. Steam is cooled at constant pressure until one-half of the mass condenses. b) T2=371.3C and P2=21.6 kg of steam at 200⁰C and 0. (b) Find the final temperature. Determine (a) the volume of the tank. b) T2=826K. At this state.83⁰C. The other side is evacuated and has a volume twice the size of the part containing the gas. (a) Show the process on a T-v diagram.4% error). and the steam tables. The partition is now removed and the gas expands to fill the entire tank. (b) the generalized compressibility chart. c) T2=750K . Determine the error involved in the first two cases.5 MPa. and (c) the steam tables. 25 percent of the volume is occupied by water and the rest by air.5 MPa and 450⁰C based on (a) the ideal-gas equation.09161m3/kg (0.Chapter 3 PBL 3–53 A piston–cylinder device contains 0.367kPa. and both may be approximated as air. CO2 is cooled at constant pressure as it flows in the pipe and the temperature of CO2 drops to 450 K at the exit. With the piston against the . Answer: T2= 568K.06297 m3/kg error 2.6% b) ʋ1= 0.1%.05667m3/kg error 3. an ideal gas.Chapter 3 PBL 3–85 Carbon dioxide gas enters a pipe at 3 MPa and 500 K at a rate of 2 kg/s. The water is heated until it reaches the saturated vapor state and the piston rests against the stops. b) T2= 573K 3–99 During a hot summer day when the air temperature is 35⁰C and the relative humidity is 70 percent.44kg/m3. ʋ2= 0. ρ1= 31. Determine the pressure at the end of the combustion process. determine (c) the error involved in the first case.76kg/m3 error 2. Also. ρ1= 32.5 m3/kg is contained in a piston-cylinder device fitted with stops so that the water supports the weight of the piston and the force of the atmosphere. ʋ2= 0. The store owner claims that the temperature of the drink is below 108⁰C. There exists the air–fuel mixture in the cylinder before the combustion and the combustion gases after it. the cylinder conditions are 1. In a gasoline engine.05472m3/kg 3–93 1-kg of carbon dioxide is compressed from 1 MPa and 200⁰C to 3 MPa in a piston-cylinder device arranged to execute a polytropic process for which PV 1. Yet the drink does not feel so cold and you are sceptical since you notice no condensation forming outside the can.2 constant.1%. Determine the volume flow rate and the density of carbon dioxide at the inlet and the volume flow rate at the exit of the pipe using (a) the ideal-gas equation and (b) the generalized compressibility chart. Determine the final temperature treating the carbon dioxide as (a) an ideal gas and (b) a van der Waals gas. Answer: P=3358kPa 3-121 Water initially at 300 kPa and 0. you buy a supposedly “cold” canned drink from a store. Answer: a) ʋ1= 0.06165 m3/kg. Can the store owner be telling the truth? 3–104 The combustion in a gasoline engine may be approximated by a constant volume heat addition process.2 MPa and 450⁰C before the combustion and 1750⁰C after it. 2. and 3. 3–125 Consider an 18-m-diameter hot-air balloon that. is heated by propane burners at a location where the atmospheric pressure and temperature are 93 kPa and 12⁰C. sketch the isotherms passing through the states and show their values. in 8⁰C. On the P-v and T- v diagrams sketch. has a mass of 120 kg when empty. What would your response be if the atmospheric air temperature were 25⁰C? Answer: T= 308K . Determine the average temperature of the air in the balloon when the balloon first starts rising. respectively. On both the P-v and T-v diagrams. the process curves passing through both the initial and final states of the water.Chapter 3 PBL stops. with respect to the saturation lines. The air in the balloon. on the isotherms. the water is further heated until the pressure is 600 kPa. together with its cage. which is now carrying two 70-kg people. Label the states on the process as 1.