5.2 Thermophysical models
Thermophysical models are used to describe cases where the thermal energy, compressibility or mass transfer is important.
OpenFOAM allows thermophysical properties to be constant, or functions of
temperature, pressure and composition. Thermal energy can be described in form
of enthalpy or internal energy. The 
relation can be described with
various equations of state or as isobaric system.
The thermophysicalProperties dictionary is read by any solver that uses
the thermophysical model library. A thermophysical model is constructed
in OpenFOAM as a pressure-temperature 
system from which
other properties are computed. There is one compulsory dictionary entry
called thermoType which specifies the complete thermophysical model that
is used in the simulation. The thermophysical modelling starts with a
layer that defines the basic equation of state and then adds further layers
for the thermodynamic, transport and mixture modelling, as listed in
Table 5.1.
model with evaluation of
internal energy 
and entropy 
model with evaluation of
enthalpy 
and entropy 
evaluated by a function with coefficients from
polynomials, from which 
, 
are evaluated 
evaluated by a function with coefficients from 
, 
are evaluated 
, 
and/or 
and total fuel mass
fraction 
and unburnt fuel
mass fraction 
and 
or internal energy 
, and compressibility 
or internal energy 
, and density 
or internal energy 
, and 
or internal energy 
, and 
or internal energy 
for unburnt
gas and combustion mixture Various combinations are available as ‘packages’, specified using, e.g.
18thermoType
19{
20 type heRhoThermo;
21 mixture pureMixture;
22 transport const;
23 thermo hConst;
24 equationOfState perfectGas;
25 specie specie;
26 energy sensibleEnthalpy;
27}
28
29mixture
30{
31 specie
32 {
33 molWeight 28.96;
34 }
35 thermodynamics
36 {
37 Cp 1004.4;
38 Hf 0;
39 }
40 transport
41 {
42 mu 1.831e-05;
43 Pr 0.705;
44 }
45}
46
47
48// ************************************************************************* //
Only certain combinations are predefined. One method to identify the possible combinations from Table 5.1 is to use a nonexistent setting for one of the entries, e.g.banana and execute the solver. OpenFOAM will issue an error message and list all possible combinations to the terminal.
5.2.1 Thermophysical property data
The basic thermophysical properties are specified for each species from input data. Data entries must contain the name of the specie as the keyword, e.g. O2, H2O, mixture, followed by sub-dictionaries of coefficients, including:
- specie
- containing i.e. number of moles, nMoles, of the specie, and molecular weight, molWeight in units of g/mol;
- thermo
- containing coefficients for the chosen thermodynamic model (see below);
- transport
- containing coefficients for the chosen transport model (see below).
The thermodynamic coefficients are ostensibly concerned with evaluating the
specific heat 
from which other properties are derived. The current thermo
models are described as follows:
- hConstThermo
- assumes a constant and a heat of fusion
which is
simply specified by a two values 
, given by keywords Cp and Hf.
- eConstThermo
- assumes a constant
and a heat of fusion 
which is
simply specified by a two values 
, given by keywords Cv and Hf.
- janafThermo
- calculates
as a function of temperature 
from a set of
coefficients taken from JANAF tables of thermodynamics. The ordered list of
coefficients is given in Table 5.2. The function is valid between a lower and
upper limit in temperature 
and 
respectively. Two sets of
coefficients are specified, the first set for temperatures above a common
temperature 
(and below 
, the second for temperatures below
(and above 
). The function relating 
to temperature
is:
(5.1) In addition, there are constants of integration,
and 
, both at high
and low temperature, used to evaluating 
and 
respectively.
- hPolynomialThermo
- calculates
as a function of temperature by a polynomial
of any order. The following case provides an example of its use:
$FOAM_TUTORIALS/lagrangian/porousExplicitSourceReactingParcelFoam/filter
The transport coefficients are used to to evaluate dynamic viscosity 
,
thermal conductivity 
and laminar thermal conductivity (for enthalpy
equation) 
. The current transport models are described as follows:
- constTransport
- assumes a constant
and Prandtl number 
which is simply specified by a two keywords, mu and Pr, respectively.
- sutherlandTransport
- calculates as a function of temperature
from a
Sutherland coefficient 
and Sutherland temperature 
, specified by
keywords As and Ts; 
is calculated according to:
(5.2) - polynomialTransport
- calculates
and 
as a function of temperature 
from a
polynomial of any order.
The following is an example entry for a specie named fuel modelled using sutherlandTransport and janafThermo:
fuel
{
specie
{
nMoles 1;
molWeight 16.0428;
}
thermodynamics
{
Tlow 200;
Thigh 6000;
Tcommon 1000;
highCpCoeffs (1.63543 0.0100844 -3.36924e-06 5.34973e-10
-3.15528e-14 -10005.6 9.9937);
lowCpCoeffs (5.14988 -0.013671 4.91801e-05 -4.84744e-08
1.66694e-11 -10246.6 -4.64132);
}
transport
{
As 1.67212e-06;
Ts 170.672;
}
}
air
{
specie
{
nMoles 1;
molWeight 28.96;
}
thermodynamics
{
Cp 1004.5;
Hf 2.544e+06;
}
transport
{
mu 1.8e-05;
Pr 0.7;
}
}
