I Is the Equation h = u + (0.185)Pv Accurate for Converting Energy Units?

[wrenchtime]

Should h = u + Pv

be h = u + (0.185)Pv (Btu/lbm)

where units for h and u are (Btu/lbm)

P (psia) and v (ft*3/lbm)

On a Temperature and specific entropy graph

h... represents the area under the curve at a constant specific pressure

u... represents the area under the curve at a constant specific volume

(0.185)Pv... represents the area between the h and u curves

I have tested the equation on several medium and it seems to work?

 

[Chestermiller]

Here’s a hint: 1 foot pound = 0.00129 BTU

 

[wrenchtime]

To convert (psia) x (ft3 / lbm) to Btu / lbm

1 Btu / lbm = (1 lbf/in2) x (1 ft3/lbm) x (1 Btu/778 ft-lbf) x (144 in2/ 1 ft2) = 0.185 Btu/lbm

The equation in metric units is

h = u + (1000) P v

With units
h = kg /kj
u = kg /kj
P = Mpa
v = m3/kg