3 replies to this topic

[ezralh]

How to determine the compressibility factor, Z for hydrogen at 300 K, 24 barg? Since it is at critical state (Tc= 33.2 K and Pc = 13.1 bar), can I assume Z = Zc = 0.305? I tried Peng/Robinson and the iterations converge to 1.0073

[serra]

you may use tabulated values or a EOS,

with Peng Robinson for hydrogen (due to its properties) for accurate values you may prefer a specific alpha function (for example a "extended" Peng Robinson),

the value of compressibility for hydrogen calculated by a Extended Peng Robinson (Prode) at 300 K 20 bar.a is 1.014 which is not too different from the value calculated by you,

[ezralh]

you may use tabulated values or a EOS,

with Peng Robinson for hydrogen (due to its properties) for accurate values you may prefer a specific alpha function (for example a "extended" Peng Robinson),

the value of compressibility for hydrogen calculated by a Extended Peng Robinson (Prode) at 300 K 20 bar.a is 1.014 which is not too different from the value calculated by you,

 

Dear Serra,

 

Does that means I can use the value from Peng- Robinson, even though it is at critical state? 0.30 and 1.0 is very very significance

[serra]

the value of critical compressibility (for hydrogen I have values a bit different from yours) is calculated from density at critical conditions (i.e. p = pc, t = tc for hydrogen),

at 300 K 20 Bar.a you are far from critical condition and as you see at these conditions even ideal gas law (i.e. Z = 1.0 instead of Z = 1.014) gives a reasonable estimate.