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Added functions for computing alternate mixture-averaged diffusion coefficients

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This commit is contained in:
Ray Speth 2012-05-11 15:27:56 +00:00
parent 49b631d346
commit 6167a724e5
2 changed files with 88 additions and 2 deletions
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23
include/cantera/transport/GasTransport.h
View file

@ -76,6 +76,29 @@ public:
*/
virtual void getMixDiffCoeffs(doublereal* const d);
//! Returns the mixture-averaged diffusion coefficients [m^2/s].
//! These are the coefficients for calculating the molar diffusive fluxes
//! from the species mole fraction gradients, computed according to
//! Eq. 12.176 in "Chemically Reacting Flow":
//!
//! \f[ D_{km}^* = \frac{1-X_k}{\Sum_{j \ne k}^K X_j/\mathcal{D}_{kj}} \f]
//!
//! @param[out] d vector of mixture-averaged diffusion coefficients for
//! each species, length m_nsp.
virtual void getMixDiffCoeffsMole(doublereal* const d);
//! Returns the mixture-averaged diffusion coefficients [m^2/s].
//! These are the coefficients for calculating the diffusive mass fluxes
//! from the species mass fraction gradients, computed according to
//! Eq. 12.178 in "Chemically Reacting Flow":
//!
//! \f[ \frac{1}{D_{km}} = \Sum_{j \ne k}^K \frac{X_j}{\mathcal{D}_{kj}} +
//! \frac{X_k}{1-Y_k} \Sum_{j \ne k}^K \frac{Y_j}{\mathcal{D}_{kj}} \f]
//!
//! @param[out] d vector of mixture-averaged diffusion coefficients for
//! each species, length m_nsp.
virtual void getMixDiffCoeffsMass(doublereal* const d);
protected:
GasTransport(ThermoPhase* thermo=0);

67
src/transport/GasTransport.cpp
View file

@ -273,7 +273,7 @@ void GasTransport::getMixDiffCoeffs(doublereal* const d)
}
doublereal mmw = m_thermo->meanMolecularWeight();
doublereal sumxw = 0.0, sum2;
doublereal sumxw = 0.0;
doublereal p = m_thermo->pressure();
if (m_nsp == 1) {
d[0] = m_bdiff(0,0) / p;
@ -282,7 +282,7 @@ void GasTransport::getMixDiffCoeffs(doublereal* const d)
sumxw += m_molefracs[k] * m_mw[k];
}
for (size_t k = 0; k < m_nsp; k++) {
sum2 = 0.0;
double sum2 = 0.0;
for (size_t j = 0; j < m_nsp; j++) {
if (j != k) {
sum2 += m_molefracs[j] / m_bdiff(j,k);
@ -297,4 +297,67 @@ void GasTransport::getMixDiffCoeffs(doublereal* const d)
}
}
void GasTransport::getMixDiffCoeffsMole(doublereal* const d)
{
update_T();
update_C();
// update the binary diffusion coefficients if necessary
if (!m_bindiff_ok) {
updateDiff_T();
}
doublereal p = m_thermo->pressure();
if (m_nsp == 1) {
d[0] = m_bdiff(0,0) / p;
} else {
for (size_t k = 0; k < m_nsp; k++) {
double sum2 = 0.0;
for (size_t j = 0; j < m_nsp; j++) {
if (j != k) {
sum2 += m_molefracs[j] / m_bdiff(j,k);
}
}
if (sum2 <= 0.0) {
d[k] = m_bdiff(k,k) / p;
} else {
d[k] = (1 - m_molefracs[k]) / (p * sum2);
}
}
}
}
void GasTransport::getMixDiffCoeffsMass(doublereal* const d)
{
update_T();
update_C();
// update the binary diffusion coefficients if necessary
if (!m_bindiff_ok) {
updateDiff_T();
}
doublereal mmw = m_thermo->meanMolecularWeight();
doublereal p = m_thermo->pressure();
if (m_nsp == 1) {
d[0] = m_bdiff(0,0) / p;
} else {
for (size_t k=0; k<m_nsp; k++) {
double sum1 = 0.0;
double sum2 = 0.0;
for (size_t i=0; i<m_nsp; i++) {
if (i==k) {
continue;
}
sum1 += m_molefracs[i] / m_bdiff(k,i);
sum2 += m_molefracs[i] * m_mw[i] / m_bdiff(k,i);
}
sum1 *= p;
sum2 *= p * m_molefracs[k] / (mmw - m_mw[k]*m_molefracs[k]);
d[k] = 1.0 / (sum1 + sum2);
}
}
}
}