From e05da2a6a5e5802a0cd6a03fc4ccd4d32c191c59 Mon Sep 17 00:00:00 2001
From: Ray Speth <speth@mit.edu>
Date: Tue, 6 Jan 2015 23:37:28 +0000
Subject: [PATCH] [Transport] Fix conversion of dipole moments from Debye to SI
 units

The existing formulas for converting Debye to SI units did not maintain the
correct dimensionality for the dipole moment. The updated formulas do not change
the results of any calculations, but the dipole moment is now correctly
expressed in Coulomb-meters.
---
 include/cantera/transport/TransportParams.h | 8 ++++----
 src/transport/TransportFactory.cpp          | 8 ++++----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/cantera/transport/TransportParams.h b/include/cantera/transport/TransportParams.h
index 6f0553ee2..2e1288317 100644
--- a/include/cantera/transport/TransportParams.h
+++ b/include/cantera/transport/TransportParams.h
@@ -218,11 +218,11 @@ public:
 
     //! The effective dipole moment for (i,j) collisions
     /*!
-     *  tr.dipoleMoment has units of Debye's. A Debye is 10-18 cm3/2 erg1/2
+     *  dipoleMoment has units of Debye. A Debye is 3.335e-30 C-m
      *
-     *    tr.dipole(i,i) = 1.e-25 * SqrtTen * trdat.dipoleMoment;
+     *    tr.dipole(i,i) = 1.e-21 / lightSpeed * dipoleMoment;
      *    tr.dipole(i,j) = sqrt(tr.dipole(i,i)*tr.dipole(j,j));
-     *  Units are  in Debye  (note, no kmol -> this is a per molecule amount)
+     *  (note, no kmol -> this is a per molecule amount)
      *
      *  Length nsp * nsp. This is a symmetric matrix.
      */
@@ -231,7 +231,7 @@ public:
     //! Matrix containing the reduced dipole moment of the interaction between two species
     /*!
      *  This is the reduced dipole moment of the interaction between two species
-     *        0.5 * tr.dipole(i,j)*tr.dipole(i,j)  (epsilon(i,j) * d * d * d);
+     *        0.5 * tr.dipole(i,j)^2 / (4 * Pi * epsilon_0 * epsilon(i,j) * d^3);
      *
      *  Length nsp * nsp .This is a symmetric matrix
      */
diff --git a/src/transport/TransportFactory.cpp b/src/transport/TransportFactory.cpp
index 0164e1529..083ec853d 100644
--- a/src/transport/TransportFactory.cpp
+++ b/src/transport/TransportFactory.cpp
@@ -147,7 +147,7 @@ void TransportFactory::makePolarCorrections(size_t i, size_t j,
     d3np = pow(tr.sigma[knp],3);
     d3p  = pow(tr.sigma[kp],3);
     alpha_star = tr.alpha[knp]/d3np;
-    mu_p_star  = tr.dipole(kp,kp)/sqrt(d3p * tr.eps[kp]);
+    mu_p_star  = tr.dipole(kp,kp)/sqrt(4 * Pi * epsilon_0 * d3p * tr.eps[kp]);
     xi = 1.0 + 0.25 * alpha_star * mu_p_star * mu_p_star *
          sqrt(tr.eps[kp]/tr.eps[knp]);
     f_sigma = pow(xi, -1.0/6.0);
@@ -466,7 +466,7 @@ void TransportFactory::setupMM(const std::vector<const XML_Node*> &transport_dat
             // reduced dipole moment delta* (nondimensional)
             doublereal d = diam(i,j);
             tr.delta(i,j) =  0.5 * tr.dipole(i,j)*tr.dipole(i,j)
-                             / (epsilon(i,j) * d * d * d);
+                             / (4 * Pi * epsilon_0 * epsilon(i,j) * d * d * d);
 
             makePolarCorrections(i, j, tr, f_eps, f_sigma);
             tr.diam(i,j) *= f_sigma;
@@ -760,10 +760,10 @@ void TransportFactory::getTransportData(const ThermoPhase& thermo, const std::ve
         }
 
         // Dipole moment of the molecule.
-        // Given in Debye (a debye is 10-18 cm3/2 erg1/2)
+        // Given in Debye (a Debye is 1e-18 statC-m or 3.3356e-30 C-m)
         double dipole = ctml::getFloat(node, "dipoleMoment");
         if (dipole >= 0.0) {
-            tr.dipole(j,j) = 1.e-25 * SqrtTen * dipole;
+            tr.dipole(j,j) = 1e-21 / lightSpeed * dipole;
             tr.polar[j] = (dipole > 0.0);
         } else {
             throw TransportDBError(i, "negative dipole moment");