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Acetone liquid properties faulty in OpenFOAM?

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Old   October 5, 2018, 13:26
Post Acetone liquid properties faulty in OpenFOAM?
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Jan
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Hi,

two other students and I are working on simulations of a spray jet flames with the sprayFoam solver. Here droplets are introduced into a jet stream (air) and accelerated by it. Due to jet stream temperature (in the experiments around 300K) evaporation takes place leading to fuel vapor in the gas phase and, secondly, additionally breakup of larger to smaller droplets is observed, which in summary leads to smaller droplets in the downstream direction of the flow.



Now the problem: if droplets of acetone are added to the flow, they immediately heat up to their boiling temperature, even if the surrounding flow temperature is decreased to 270 K. Furthermore, they generate heat during evaporation, which contradicts the natural physical principles.

In order to check whether the error is due to our simulation (boundary and/or initial conditions), we also carried out the simulation with ethanol and n-heptane, which leads to the normal expected results of cooling the gas.


Therefore I have examined the source code for the liquids, and determined a deviation at the entry of the liquid enthalpy in comparison to all other liquids.

In the file "./thermophysicalModels/thermophysicalProperties/liquidProperties/C3H6O/C3H6O.C" i found the entry constants for the liquid enthalpy for acetone to be
h_
(
2571201.780143,
2334.71074380165,
-1.52376033057851,
0.00162821395775941,
2.96573691460055e-06,
0.0
),

The calculation of the liquid enthalpy is done by the NSRDS0 function is done in "thermophysicalFunctions/NSRDSfunctions/NSRDSfunc0/NSRDSfunc0.H", and it is defined as follows:

NSRDSfunc0
(
const scalar a,
const scalar b,
const scalar c,
const scalar d,
const scalar e,
const scalar f
);

scalar f(scalar, scalar T) const
{
return ((((f_*T + e_)*T + d_)*T + c_)*T + b_)*T + a_;
}


Calculating the liquid enthalpy for different substances (in [J/kg]) at a temperature of 300 degrees (e.g. ethanol, butanol, heptane and others), all results are in the range between -2*10^6 and -8*10^6. Only the value of acetone is 3.476*10^6.

According to the source code "Liquidproperties.C" the enthalpy is calculated to the reference value at 298.13 Kelvin.

For this reason I think that there is an error in the constants of h_, unfortunately we don't have access to the required database to verify or falsify the assumption.

However, in order to investigate the thesis further, I have rewritten the substance properties of "C3H6O.C" so that they contain the "h_" constants of ethanol and thus performed the simulation again. In this simulation the droplets behaved as expected, they heated slowly and withdrew heat from the environment during a phase transition to the gaseous phase.


It would be good if someone could confirm this thesis of the wrong substance properties and even better if someone could access the right substance constants.


Yours sincerely
Jan Klingenstein
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Old   October 12, 2018, 01:05
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Checking ... in progress. Thanks for the hint.

Edit. Out of the box, it seems that the first coefficient a_ has a wrong sign. I will give feedback soon.
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Old   October 12, 2018, 04:01
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Quote:
Originally Posted by Tobi View Post
Edit. Out of the box, it seems that the first coefficient a_ has a wrong sign. I will give feedback soon.
I also checked and changed that. With the newly compiled code, the droplets have still heated up to boiling temperature immediately and continue to give off heat. Currently I am using factors I have obtained from a linear interpolation between 1-butanol and ethanol. This is certainly not correct, but gives the desired results.



The factors used for this case are:
h_
(
-5532589.08613163,
1325.788835782,
4.0829994247,
-0.0111765881,
0.0000212843462929658,
0.0
),

Thanks for your help already,

Jan
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Old   October 12, 2018, 06:52
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Hi,

as I am aware of the complexity of chemical formulas, I am not sure if this is a sign error now or if it is correct. Thus, I reported the problem (https://bugs.openfoam.org/view.php?id=3085). Additionally I used another similar species (yours are different, hydroxyl OH vs single O species) and figured out similar behavior. Changing the first value will not help (slope is to low).
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Last edited by Tobi; October 13, 2018 at 04:56.
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