diff --git a/src/fvOptions/sources/derived/solidificationMeltingSource/solidificationMeltingSource.H b/src/fvOptions/sources/derived/solidificationMeltingSource/solidificationMeltingSource.H
index 441ee1a08..7b3b0f400 100644
--- a/src/fvOptions/sources/derived/solidificationMeltingSource/solidificationMeltingSource.H
+++ b/src/fvOptions/sources/derived/solidificationMeltingSource/solidificationMeltingSource.H
@@ -31,10 +31,28 @@ Description
     The isotherm phase change occurs at the melting temperature, \c Tsol (= \c
     Tliq). The not isotherm phase change occurs between solidus and liquidus
     temperature, \c Tsol < \c Tliq respectively, as long as the melt fraction is
-    greater than the max eutectic melt fraction, \c alpha1e (0 =
-    pure_substance, 1 = eutectic_mixture is not permitted) , i.e. eutectic to
-    initial solvent concentration difference, where a linear eutectic melt
-    fraction to temperature relation is considered - lever rule.
+    greater than the max eutectic melt fraction, \c alpha1e (0 = pure_substance,
+    1 = eutectic_mixture is not permitted), where a linear eutectic melt
+    fraction to temperature relation is considered; e.g. given a specific
+    quantity of a binary system, \c alpha1 is its melt fraction and \c alpha0 is
+    its solid fraction, such that \c alpha0 = 1 - \c alpha1 therefore, assuming
+    infinite solute diffusion, the quantity of a component in solid phase is (1
+    - \c alpha1) * \c CS where \c CS is the solid concentration of the
+    considered component and the quantity of a component in liquid phase is \c
+    alpha1 * \c CL where \c CL is the melt concentration of the considered
+    component; considering that the total quantity of a component must be equal
+    to the sum of the quantities of the considered component in the liquid and
+    solid phases, if \c C0 is the initial concentration of the considered
+    component before the phase change, then:
+    \c C0 = (1 - \c alpha1) * \c CS + \c alpha1 * \c CL      (lever rule)
+    from which: \c alpha1 = (\c C0 - \c CS) / (\c CL - \c CS)
+    and thus:
+    - for a miscible binary system \c alpha1e = 0;
+    - for a binary system not miscible at solid state
+      \c alpha1e = \c C0 / \c CLE where \c CLE is eutectic melt concentration;
+    - for a binary system partially-miscible at solid state
+      \c alpha1e = (\c C0 - \c CSE) / (\c CLE - \c CSE) where CSE is eutectic
+      solid concentration of the relative solid solution.
 
     The presence of the solid phase in the flow field is incorporated into the
     model as a momentum porosity contribution; the energy associated with the