Answer:
The expansion work is 71.24 kJ and heat transfer is -16.89 kJ
Explanation:
From ideal gas law,
Initial volume (V1) = nRT/P
n is the number of moles of air in the cylinder = mass/MW = 0.1/29 = 0.00345 kgmol
R is gas constant = 8314.34 J/kgmol.K
T is initial temperature = 1527 °C = 1527+273 = 1800 K
P is initial pressure = 4 MPa = 4×10^6 Pa
V1 = 0.00345×8314.34×1800/(4×10^6) = 0.013 m^3
V2 = 10×V1 = 10×0.013 = 0.13 m^3
The process is a polytropic expansion process
polytropic exponent (n) = 1.5
P2 = P1(V1/V2)^n = 4×10^6(0.013/0.13)^1.5 = 1.26×10^5 Pa
Expansion work = (P1V1 - P2V2) ÷ (n - 1) = (4×10^6 × 0.013 - 1.26×10^5 × 0.13) ÷ (1.5 - 1) = 35620 ÷ 0.5 = 71240 J = 71240/1000 = 71.24 kJ
Heat transfer = change in internal energy + expansion work
change in internal energy (∆U) = Cv(T2 - T1)
T2 = PV/nR = 1.26×10^5 × 0.13/0.00345×8314.34 = 571 K
Cv = 20.785 kJ/kgmol.K
∆U = 20.785(571 - 1800) = -25544.765 kJ/kgmol × 0.00345 kgmol = -88.13 kJ
Heat transfer = -88.13 + 71.24 = -16.89 kJ
