Argon in a light bulb is at 90 kPa and heated from 20°C to 60°C with electrical power. Find the total entropy generation per unit mass of argon.
Answer: C
Energy Eq. : m(u2 – u1) = 1W2 electrical
Entropy Eq.: s2 – s1 = ∫ dq/T + 1s2 gen = 1s2 gen
Process: v = c & ideal gas ∴ P2/ P1 = T2/T1
1s2 gen = s2 – s1 = Cp ln(T2/T1) – R ln (P2/P1)
= Cpln(T2/T1) – R ln(T2/T1) = Cv ln(T2/T1)
= 0.312 ln{(60+273)/(20+273)} = 0.04 kJ/kg K.