Question

A system contains 0.2 m3 of air at a pressure of 400 kPa and 200°C. It is expanded polytropically (n=1.2) till the pressure falls to 150 kPa. The air is then heated at constant pressure till its enthalpy increases by 80 kJ. Determine:   i. the final volume ii. the total work done

Answer 1

Air is assumed to be ideal.

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440 41 Isoki 1-2 edytropic proken Pvtwist 7, 22000 - 473k R= 287 9/4g-k PY BV >440402 =isor 12=0.49 m3 • ③ - is gsobonic process. IDH = mo DT = mol 124- 10.6423 C 0.2m² ry 0.6 to ke 440x1080.2 - mass is somos ms PV RT aroughout = state lsoxio xog-0.648311 RT - 395.2 k- 2678 Pr DH = 80KT 6=1.005 Kilke tc 3 202_0648x1.00 $ : -395.213 → h = 518. Osk i nocen 0.49 © - a b v is gsobow'c process → V To- T; > Dive 39524 578105 - TV3 = 0.64 23 m3 = final roume 0-0 Total & work done during 10 work Werk done during done = p. v.-Pk - Pal A-2) ------- Tunoxlox 0.2- 150818 x 0.49) + Isox 1038 (0.64 23-0.49) 1.2-1 95.3u5 X 10 J = 95.345 KT W =

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