M P Bm Rt V P Kg Kj U V C T Kpa P: Solusi Quiz 5

Solusi Quiz 5 Soal : Siklus Otto ideal memiliki rasio kompresi 8. Pada awal proses kompresi udara ada pada 95 kPa dan 27oC serta 750 kJ/kg kalor di transfer ke udara selama proses volume konstant. Tentukan : a. P dan T tiap akhir proses siklus b. wout,net c. ηth d. MEP Solusi : a. P1 = 95kPa;T1 = 27°C ; vr1 = 621.2; u1 = kj / kg ; p r1 = 1.3860

v1 =

RT1 m3 8.319.300 = = 0.906 BM udara P1 kg 29.95

Pr oses1 − 2 : isentropik v v v1 vr1 621.2 = ; v r 2 = v r1 2 = r 1 = = 77.65 v1 r v2 vr 2 8 dari tabel diperoleh : T2 = 673.09 K = 400.09°C ; p r 2 = 24.89; u 2 = 491.22kJ / kg P2 = P1

pr 2 24.89 = 95kPa = 1.706 MPa p r1 1.386

q 23 = u 3 − u 2 ; u 3 = q 23 + u 2 = 750kJ / kg + 491.22kJ / kg = 1241.22kJ / k dari tabel diperoleh : T3 = 1538.7 K = 1265.7°C ; p r 3 = 670.43; v r 3 = 6.587

P3 = P2

T3 1538.7 K = 1706kPa = 3.89996 MPa 673.09 K T2

v4 = v r 3 .r = 6.587.8 = 52.696 v3 dari tabel diperoleh : T4 = 774.6 K = 501.6°C ; p r 4 = 42.24; u 4 = 571.754kJ / kg vr 4 = vr 3

pr 4 42.24 = 3899.96kPa = 245.7kP pr 3 670.43 = u 4 − u1 = 571.754kJ / kg − 214.07kJ / kg = 357.7kJ / kg

P4 = P3 b.

q out

wnet ,out = qin − q out = 750kJ / kg − 357.7 kJ / kg = 392.3kJ / kg wnet ,out

392.3kJ / kg = 0.523 = 52.3% 750kJ / kg qin wnet ,out wnet ,out wnet ,out 392.3kJ / kg kJ = = = 7 = 494.86 3 d. MEP = 3 7 1 v1 − v 2 v1 − 8 v1 m 8 v1 8 0.906m / kg c. η th =

=