Question

Air is heated from 540 R to 640 R at V = C. Find ₁q₂? What if from 2400 to 2500 R? 

Answer 1

Process: V = C → ₁W₂ = Ø

Energy Eq.: u₂ − u₁ = ₁q₂ – 0 → ₁q₂ = u₂ − u₁ 

Read the u-values 

(a) ₁q₂ = u₂ − u₁ = 109.34 – 92.16

= 17.18 Btu/lbm 

(b) ₁q₂ = u₂ − u₁ = 474.33 – 452.64 

= 21.7 Btu/lbm

case (a) Cv ≈ 17.18/100

= 0.172 Btu/lbm R, 

case b) C_v ≈ 21.7/100 = 0.217 Btu/lbm R (26 % higher)