Question

I have 4 lbm of liquid water at 70 F, 15 psia. I now add 20 Btu of energy at a constant pressure. How hot does it get if it is heated? How fast does it move if it is pushed by a constant horizontal force? How high does it go if it is raised straight up? 

Answer 1

a) Heat at 100 kPa.

Energy equation:

E₂ – E₁ = ₁Q₂ – ₁W₂ = ₁Q₂ – P(V₂ – V₁) = H₂ – H₁= m(h₂ – h₁)

h₂ = h₁ + ₁Q₂/m

= 38.09 + 20/4 = 43.09 Btu/lbm

Back interpolate in   T₂ = 75 F (We could also have used ∆T = ₁Q₂/mC = 20 / (4×1.00) = 5 F)

b) Push at constant P. It gains kinetic energy