Question

QUESTION 3 A 0.25m of saturated liquid refrigerant-134a at 80°C is contained in frictionless insulated piston-cylinder device as shown in Figure Q2(b). A paddle-wheel is placed inside the cylinder chamber to stir the refrigerant-134a and the paddle wheel transfer a total work of 245 kJ to the fluid. Moreover, a 440 V and 9 amp of resistor is also placed inside the cylinder chamber to heat the refrigerant-134a. With the aid of a P-V diagram, determine the time taken for the final volume of the piston- cylinder device to be three times its initial volume at constant pressure of the refrigerant-134a. (Note for constant pressure process Pa=P2) R-134a we Figure Q2b

Answer 1

Initial state: Refrigerant R-134a Volume, V = 0.25m3 saturated liquid Temperature, Ti = 80 c R-134 a Ws Specific volume, &,= = 0.0010772 We m3lke = Q. Internal energy, u, = ug = $171.400 Kilug P = pressure = 2635.3 kPa x = 2.6353 MP a = 26.353 bar = pq (final presure) Man m= = 232.0832 Kg m a the ist law of thermodynamin final volume, V2 = 3v = 0.75 m3 i specific volume, 22 = Ver = 0.0032316 m²/ks V2 = 2 + ax (vg - Vf) @ 80°c = 0.0032316 = 0.0010772 + ax (0.00 6436- 0.0010772) - - x = 0.402 x = 0. 402 (drynen fraction) Internal energy uz aug + nxufg. - 171.40 + 0.402% 92.23 - 208.47 og kJ/kg for closed system: ou = R-W kPa - mug-u)= vit + 24 5x103 Wtwork transfer =- 245 kJ (-ve because work is done on the System) vi =) 232.0832x (208.479 - 171.40) x 103 = 0.25m3 -0.75m3 = 440x gxt +2457103 - It=2111.23 seconds = 35 minutes 11:23 seconds R 4 The time taken for the final volume of the piston cylinder device to be three time, its initial volume @p=c. PAL ② Pre 2635.37