Question

‏1 kg of Dry saturated steam at 10 bar expand reversibly and polytropically to a pressure of bar if the index of expansion is 1.1 ,

Find the following ‏

1)The value of Entropy at start of the process is ‏

2)The value of Internal Energy at start of the process is ‏

3)The value of Entropy at end of the process is

4) The value of Internal energy at end of the process is

5) The change of entropy between start and end is 6)The value of heat supply and state its supplied or rejected

7)The value of work done is bc

Answer 1

Solution in Given data mand of the steam Finaal 1 kg Initial pressure, Pi = loboro pressure, P 1 bat index of expansion, n= 1.1 (1) Entropy ont the start of the process" (S2):- Refening The smodyna mics tables for day saturated steam out find :- Sg@lobera 6.5864 KJ 10 bar ملا kg-k Sq = 6.5864 KJ kg-k And (ii) energy Internal ener at the start of the process (4₂) Refering Thermodyamics tables for dry sertursented team at io bar we find @ 10 beira Com 2582.64 KJ U = 2582.64 KJ/kg 25/2

Now for Polytropic process we Com) have: 3 P n On V₂ = 4 P2 Dolg444om? V = Vg @lobar V2 = (0.194440x{ let x2= quality (drynese fraction) the steam at the end lag (Hot 1.5970? of of the Also process. 2= x2 Vga vga = vg @ 1 bars = 1.694 m?lang 727 V₂ 1.577 T. 694 0.93 So, Uga (1) Entropy out the end of the process (52) given by : S₂ can be

Uz can be Up = Sfga S = Sfat x Sf2 = Sp @ 1 hors = 1.3025 KJ Sfg @ 1 bort 6.os 68 KJ Spg? kg-k regk S2 = (1.3025)+ (0.93)(6.0568) s, 6.935 KJ kg-k And Internal est the end (iv) energy of the process (42) : ų= (1-x2) Upat 41704 kJ Ug2 = 4g @ 1 bar = 2506.12 Uz =(1-0.93)(417.4)+(0,33) (2506-12) Ц, kg Any Ufgr KJ/kg 12 kJ/kg 5 2360 KJ (w) change in eutropy between Start and end CAS)

AS = Sy-Si As = 6.935- 6.5864 AS = 0.3486 KJ kg-k (vi) Heat supplied (01-2):- Q,-2 Can be given by: Q-2= (-4₂) + lool Piv,- Pale) n-)

Q1-2 [ (2260-2582164) too [(loxo.194440) 12.64 + 171.571 1.1) 01-2=(-222 64) + (367.4) Q1-2 144.76 kJ kJ/kg Ang As 1 <n<r where n=1.1 o=1.4 the The heat is system, rejected by

(vii) work done (Wire) Wi-2 came be giver by: Wi-2= 100 (PV-P2 V 2) M-) Wi-2=100 100(10x 0.194449) - (1x1.577)] 1.1 - Wi-z=367.4 kJ kJ/kg Ang