Question

1 A piston-cylinder device initially contain 0.4 m3 of 1.8- kg saturated liquid water and steam mixture at 110 kPa. A electric heater in the device is turned on and passes a current of 1.7 A from a 120-V source. Only transfer of electrical work and boundary work exist. The piston initially rests on a set of stops, and a pressure of 200 kPa is required to move the piston. Afterwards the system continues to raise the piston and eventually reaches the temperature of 400 Celcius. Find the initial quality of the system, initial internal energy (kj/kg), time it takes for the system to just move the piston (hours), final volume of system (m3), and total time it takes for the system to reach its final state (hours)

Answer 1

Date: Page: Taking values from steam table : (At Pa 110 kla) 428.65 j KI kg ug 2508.79 kJ/kg Specific : le = interd energy 1.549 N L- specific volume = 0.00104 m² kg m? kg V= 0.4 m² mass of sat lie water, m= 1.8 kg . V m v 0.222 1.8 awe know that, uft x Vfg ; x = quality or milky V = 21 0.222 Vet x ( dg - Vel 0.00104 + x ( 1.549 - 0.00109) 0.142 - 0.142 ... Initial quality of steam = Also, 428.65) - uft x Ugg alugue) 2508.79 428.65+ (0.142) x ( 2008 724, 03 Kg u 2) ui

Date : Page: 724.03 i. Initial specific internal energy of the System law thermo dy na mies 19 Using 1st 86 det &W where &W= PdV here, du = 0 ( vol of the system is constant) v = vz ?, SC du 8 = SU Again, from steam table: (At psat = 200 kPa) SOY.47 KI C- ug 2529.24 K3/19 ve 0.00106 m² 0.885 m3 lug . o 222 0.222 0,222 = 0.00 106 + x (0.885- 0.00106) 0.25

Date: Page : u 504,47 + (0.25)+(2529.24 - 009.47) - KJ 1010.66 AU E AU m 2) AU AU = SU mou mų - Ui) 18 Kg x ( 1010.66 al 724,03 kJ kg 515 93 KI 9 - AV 515 93 For electric heater, Power (voltage ) x (current) 120 V x 1.7 A 204 W electric Energy Power x time 204 x t, is converted to heat 204 t, 2 103 x 515.93= 204 t, t 2529.66 sec 2529.06 3600 2 t, 0.702 hours This energy 8

Time taken Time it takes for the system move the piston hors 0.702 to just Now, At T= 400°c P = 200 Kla ht 3277 1549 kg V final m. vf 1.8 x 1.549 2.78 m m² final vol of the system 2.78 m² h = & ut pu h = 10 LO. 66 t 200 x 0.222 10 55 KJ/kg hr h

current ml hf - hr) (Powen), x (fernt) A time) o -> tz 18 (3277. tz 1855) x10 - 120x1.7* 19605. 88 sec 19605.88 36.00 tz 5.446 hr Total time for the system to reach its final state t, & tz 0.702t 5.446 hours