Question

Air (MW = 29 g/mol) is initially at 202 °C and 2 atm. At some time later, it is at 677 °C and 8 atm. What is the amount of work per unit mass, done if the process involved was isobaric from v₁ to v₂ and then ischoric from p₁ to p₂? Draw the process on a P-v diagram.

Answer 1

To calculate the work done first we need to calculate specific volume at all salient points as shown below then calculate work done :

(1) Saluti دامون 0X melamlar weight of air (MW) = 2g glinal initial temperature (tj = 200 °C T = (202 + 273k T = 475k intial pressure (P.) 2 atm. final temperature (ta) 677°C Iz = (677 + 273)k Iz = 950k final pressure (P2) = 3 atm. ΟΥ P-u diagram - Satin pl P risochoric batt 12 atm 21 (isobarich 1 → v (mlig New for air characteristic (R) given by - gas Censtant R M

Date Page No. whore ܡ universal Constant gas 287 51 kg k R = 8314 ag Now we krow P, 9, vi that RT RTL Pl 287 x 475 2x 105 = و 0.6816 m²/kg. va Suosille 287 X 950 RP2 P2 &xcos To z = U2' = 0.3408 m²lig نی Now work done in process (91-2) will be because isochoric zero proces, home Not work clone is entire proces is given by Wnet = Pici- vil 2x105 (0.3408 -0.6816) Whet= -68.160 kJ /kg. that work hore negective sign shows done on the system, is