Thermodynamics

268 | Thermodynamicstank exists in the vapor phase only. At this point the valve isclosed. Determine (a) the final temperature in the tank, (b) themass of refrigerant that has entered the tank, and (c) the heattransfer between the system and the surroundings.5–129E A 3-ft 3 rigid tank initially contains saturated watervapor at 300°F. The tank is connected by a valve to a supplyline that carries steam at 200 psia and 400°F. Now the valveis opened, and steam is allowed to enter the tank. Heat transfertakes place with the surroundings such that the temperaturein the tank remains constant at 300°F at all times. Thevalve is closed when it is observed that one-half of the volumeof the tank is occupied by liquid water. Find (a) the finalpressure in the tank, (b) the amount of steam that has enteredthe tank, and (c) the amount of heat transfer. Answers:(a) 67.03. psia, (b) 85.74 lbm, (c ) 80,900 Btu5–130 A vertical piston–cylinder device initially contains0.01 m 3 of steam at 200°C. The mass of the frictionless pistonis such that it maintains a constant pressure of 500 kPainside. Now steam at 1 MPa and 350°C is allowed to enterthe cylinder from a supply line until the volume inside doubles.Neglecting any heat transfer that may have taken placeduring the process, determine (a) the final temperature of thesteam in the cylinder and (b) the amount of mass that hasentered. Answers: (a) 261.7°C, (b) 0.0176 kg5–131 An insulated, vertical piston–cylinder device initiallycontains 10 kg of water, 6 kg of which is in the vapor phase.The mass of the piston is such that it maintains a constant pressureof 200 kPa inside the cylinder. Now steam at 0.5 MPa and350°C is allowed to enter the cylinder from a supply line untilall the liquid in the cylinder has vaporized. Determine (a) thefinal temperature in the cylinder and (b) the mass of the steamthat has entered. Answers: (a) 120.2°C, (b) 19.07 kgP = 200 kPam 1 = 10 kgH 2 Oobserved that the tank contains saturated liquid at 1.2 MPa.Determine (a) the mass of the refrigerant that has entered thetank and (b) the amount of heat transfer. Answers: (a) 128.4kg, (b) 1057 kJ5–133 A 0.3-m 3 rigid tank is filled with saturated liquidwater at 200°C. A valve at the bottom of the tank is opened,and liquid is withdrawn from the tank. Heat is transferred tothe water such that the temperature in the tank remains constant.Determine the amount of heat that must be transferredby the time one-half of the total mass has been withdrawn.H 2 OV = 0.3 m 3T = 200°CSat. liquid1m e = – m2 1FIGURE P5–1335–134 A 0.12-m 3 rigid tank contains saturated refrigerant-134a at 800 kPa. Initially, 25 percent of the volume is occupiedby liquid and the rest by vapor. A valve at the bottom ofthe tank is now opened, and liquid is withdrawn from thetank. Heat is transferred to the refrigerant such that the pressureinside the tank remains constant. The valve is closedwhen no liquid is left in the tank and vapor starts to comeout. Determine the total heat transfer for this process.Answer: 201.2 kJ5–135E A 4-ft 3 rigid tank contains saturated refrigerant-134a at 100 psia. Initially, 20 percent of the volume is occupiedby liquid and the rest by vapor. A valve at the top of thetank is now opened, and vapor is allowed to escape slowlyfrom the tank. Heat is transferred to the refrigerant such thatthe pressure inside the tank remains constant. The valve isclosed when the last drop of liquid in the tank is vaporized.Determine the total heat transfer for this process.Q inFIGURE P5–131P i = 0.5 MPaT i = 350°C5–132 A 0.12-m 3 rigid tank initially contains refrigerant-134a at 1 MPa and 100 percent quality. The tank is connectedby a valve to a supply line that carries refrigerant-134a at 1.2MPa and 36°C. Now the valve is opened, and the refrigerantis allowed to enter the tank. The valve is closed when it isR-134aSat. vaporP = 100 psiaV = 4 ft 3FIGURE P5–135EQ in