|
[Sponsors] |
Peng-Robinson roots problems for H2 at normal temperature |
![]() |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
![]() |
![]() |
#1 |
New Member
Luc Cena
Join Date: Oct 2022
Posts: 1
Rep Power: 0 ![]() |
Hi All
![]() I have problems to work with Peng Robinson EoS for temperatures way above the Tcr of H2. I am using the cardano method base to find the roots with the hydrogen properties: Tc=33K ; Pc=1.32MPa ; omega=-0.22 Target is to find the molar volume for normal pressure temperature range, like T1=20°C / P1=10MPa, so temperature and pressure are way above the critical values. Well, I was expecting only one root because both P/T are above the critical values, but intermediate parameters analysis ( b^2 / 4 ) + ( m^3 / 27 ) is negative so I should expect 3 real roots with the one in the middle meaningless as usual. I can solve the cubic with the following solution: Z³ - 0.933 * Z² - 0.105 * Z + 0.002 = 0 Z1= -0.117 Z2= +1.034 Z3= +0.017 All three are correct, so it looks ok, three solutions real, not complex as expected. But here comes the problems: First solution is negative (!!!) : Theoretically it should provide the bubble point with but Vm= Z1 * R * T / p is negative if I use a negative Z, it does not make sense. Second solution is above 1 : Theoretically all solutions should be in the range [0;1] if I understand the theory well. Third solution is the middle one : I should not consider it. Can you tell me why this math behaviour for H2? Am I too far from the critical point for this gas and I cannot use PR EOS or am I doing anything wrong? I am obtaining the attached by plotting the data but I do not think that going negative with the volume is somethig good lol. Any suggestion?? Thanks |
|
![]() |
![]() |
![]() |
Tags |
hydrogen, peng-robinson eoe, real fluids equation |
|
|
![]() |
||||
Thread | Thread Starter | Forum | Replies | Last Post |
Calculation of the Governing Equations | Mihail | CFX | 7 | September 7, 2014 06:27 |
ATTENTION! Reliability problems in CFX 5.7 | Joseph | CFX | 14 | April 20, 2010 15:45 |
Problems referencing to temperature | andreas | CFX | 7 | October 30, 2006 07:26 |
Problems with temperature jump at the boundary | tsjb00 | OpenFOAM Running, Solving & CFD | 4 | August 25, 2005 13:33 |
Temperature calculation problems | Julie Polyakh | Siemens | 1 | January 15, 2002 20:50 |