diff --git a/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/phasesSystem/phasePair/phasePairKey/phasePairKey.C b/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/phasesSystem/phasePair/phasePairKey/phasePairKey.C
index 5115d8ddc7..1604ec51d4 100644
--- a/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/phasesSystem/phasePair/phasePairKey/phasePairKey.C
+++ b/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/phasesSystem/phasePair/phasePairKey/phasePairKey.C
@@ -27,14 +27,6 @@ License
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
-Foam::phasePairKey::hash::hash()
-{}
-
-
-Foam::phasePairKey::phasePairKey()
-{}
-
-
 Foam::phasePairKey::phasePairKey
 (
     const word& name1,
@@ -71,12 +63,8 @@ Foam::label Foam::phasePairKey::hash::operator()
                 word::hash()(key.second())
             );
     }
-    else
-    {
-        return
-            word::hash()(key.first())
-          + word::hash()(key.second());
-    }
+
+    return word::hash()(key.first()) + word::hash()(key.second());
 }
 
 
@@ -88,14 +76,13 @@ bool Foam::operator==
     const phasePairKey& b
 )
 {
-    const label c = Pair<word>::compare(a,b);
+    const auto cmp = Pair<word>::compare(a,b);
 
     return
+    (
         (a.ordered_ == b.ordered_)
-     && (
-            (a.ordered_ && (c == 1))
-         || (!a.ordered_ && (c != 0))
-        );
+     && (a.ordered_ ? (cmp == 1) : cmp)
+    );
 }
 
 
@@ -121,7 +108,7 @@ Foam::Istream& Foam::operator>>(Istream& is, phasePairKey& key)
     {
         key.ordered_ = false;
     }
-    else if(temp[1] == "to")
+    else if (temp[1] == "to")
     {
         key.ordered_ = true;
     }
@@ -130,8 +117,8 @@ Foam::Istream& Foam::operator>>(Istream& is, phasePairKey& key)
         FatalErrorInFunction
             << "Phase pair type is not recognised. "
             << temp
-            << "Use (phaseDispersed to phaseContinuous) for an ordered"
-            << "pair, or (phase1 and pase2) for an unordered pair."
+            << "Use (phaseDispersed to phaseContinuous) for an ordered pair, "
+            << "or (phase1 and phase2) for an unordered pair."
             << exit(FatalError);
     }
 
diff --git a/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/phasesSystem/phasePair/phasePairKey/phasePairKey.H b/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/phasesSystem/phasePair/phasePairKey/phasePairKey.H
index babb4b887b..13d711eab4 100644
--- a/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/phasesSystem/phasePair/phasePairKey/phasePairKey.H
+++ b/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/phasesSystem/phasePair/phasePairKey/phasePairKey.H
@@ -40,6 +40,15 @@ SourceFiles
 namespace Foam
 {
 
+// Forward declarations
+class phasePairKey;
+
+bool operator==(const phasePairKey& a, const phasePairKey& b);
+bool operator!=(const phasePairKey& a, const phasePairKey& b);
+
+Istream& operator>>(Istream& is, phasePairKey& key);
+Ostream& operator<<(Ostream& os, const phasePairKey& key);
+
 /*---------------------------------------------------------------------------*\
                          Class phasePairKey Declaration
 \*---------------------------------------------------------------------------*/
@@ -48,29 +57,6 @@ class phasePairKey
 :
     public Pair<word>
 {
-public:
-
-        class hash
-        :
-            public Hash<phasePairKey>
-        {
-        public:
-
-            // Constructors
-
-                //- Construct null
-                hash();
-
-
-            // Member operators
-
-                //- Generate a hash from a phase pair key
-                label operator()(const phasePairKey& key) const;
-        };
-
-
-private:
-
     // Private data
 
         //- Flag to indicate whether ordering is important
@@ -79,12 +65,20 @@ private:
 
 public:
 
+        //- Ordered or unordered hashing of word pair
+        struct hash
+        {
+            //- Generate a hash from a phase pair key
+            label operator()(const phasePairKey& key) const;
+        };
+
+
     // Constructors
 
         //- Construct null
-        phasePairKey();
+        phasePairKey() {} // = default
 
-        //- Construct from names and the ordering flag
+        //- Construct from names and optional ordering flag
         phasePairKey
         (
             const word& name1,
@@ -93,7 +87,7 @@ public:
         );
 
 
-    // Destructor
+    //- Destructor
     virtual ~phasePairKey() = default;
 
 
@@ -105,16 +99,16 @@ public:
 
     // Friend Operators
 
-        //- Test if keys are equal
+        //- Test for equality
         friend bool operator==(const phasePairKey& a, const phasePairKey& b);
 
-        //- Test if keys are unequal
+        //- Test for inequality
         friend bool operator!=(const phasePairKey& a, const phasePairKey& b);
 
-        //- Read from stdin
+        //- Read from Istream
         friend Istream& operator>>(Istream& is, phasePairKey& key);
 
-        //- Write to stdout
+        //- Write to Ostream
         friend Ostream& operator<<(Ostream& os, const phasePairKey& key);
 };
 
diff --git a/applications/solvers/multiphase/reactingEulerFoam/phaseSystems/phasePair/phasePairKey/phasePairKey.C b/applications/solvers/multiphase/reactingEulerFoam/phaseSystems/phasePair/phasePairKey/phasePairKey.C
index c3cebe7b5c..326c333889 100644
--- a/applications/solvers/multiphase/reactingEulerFoam/phaseSystems/phasePair/phasePairKey/phasePairKey.C
+++ b/applications/solvers/multiphase/reactingEulerFoam/phaseSystems/phasePair/phasePairKey/phasePairKey.C
@@ -63,12 +63,8 @@ Foam::label Foam::phasePairKey::hash::operator()
                 word::hash()(key.second())
             );
     }
-    else
-    {
-        return
-            word::hash()(key.first())
-          + word::hash()(key.second());
-    }
+
+    return word::hash()(key.first()) + word::hash()(key.second());
 }
 
 
@@ -80,14 +76,13 @@ bool Foam::operator==
     const phasePairKey& b
 )
 {
-    const label cmp = Pair<word>::compare(a,b);
+    const auto cmp = Pair<word>::compare(a,b);
 
     return
+    (
         (a.ordered_ == b.ordered_)
-     && (
-            (a.ordered_ && (cmp == 1))
-         || (!a.ordered_ && (cmp != 0))
-        );
+     && (a.ordered_ ? (cmp == 1) : cmp)
+    );
 }
 
 
diff --git a/applications/solvers/multiphase/reactingEulerFoam/phaseSystems/phasePair/phasePairKey/phasePairKey.H b/applications/solvers/multiphase/reactingEulerFoam/phaseSystems/phasePair/phasePairKey/phasePairKey.H
index dae60dafcc..919ddaf7a7 100644
--- a/applications/solvers/multiphase/reactingEulerFoam/phaseSystems/phasePair/phasePairKey/phasePairKey.H
+++ b/applications/solvers/multiphase/reactingEulerFoam/phaseSystems/phasePair/phasePairKey/phasePairKey.H
@@ -41,14 +41,13 @@ namespace Foam
 {
 
 // Forward declarations
-
 class phasePairKey;
 
-bool operator==(const phasePairKey&, const phasePairKey&);
-bool operator!=(const phasePairKey&, const phasePairKey&);
+bool operator==(const phasePairKey& a, const phasePairKey& b);
+bool operator!=(const phasePairKey& a, const phasePairKey& b);
 
-Istream& operator>>(Istream&, phasePairKey&);
-Ostream& operator<<(Ostream&, const phasePairKey&);
+Istream& operator>>(Istream& is, phasePairKey& key);
+Ostream& operator<<(Ostream& os, const phasePairKey& key);
 
 
 /*---------------------------------------------------------------------------*\
@@ -64,11 +63,13 @@ class phasePairKey
         //- Flag to indicate whether ordering is important
         bool ordered_;
 
+
 public:
 
+        //- Ordered or unordered hashing of word pair
         struct hash
         {
-            // Generate a hash from a phase pair key
+            //- Generate a hash from a phase pair key
             label operator()(const phasePairKey& key) const;
         };
 
@@ -78,7 +79,7 @@ public:
         //- Construct null
         phasePairKey() {} // = default
 
-        //- Construct from names and the ordering flag
+        //- Construct from names and optional ordering flag
         phasePairKey
         (
             const word& name1,
@@ -87,7 +88,7 @@ public:
         );
 
 
-    // Destructor
+    //- Destructor
     virtual ~phasePairKey() = default;
 
 
@@ -99,16 +100,16 @@ public:
 
     // Friend Operators
 
-        //- Test if keys are equal
+        //- Test for equality
         friend bool operator==(const phasePairKey& a, const phasePairKey& b);
 
-        //- Test if keys are unequal
+        //- Test for inequality
         friend bool operator!=(const phasePairKey& a, const phasePairKey& b);
 
-        //- Read from stdin
+        //- Read from Istream
         friend Istream& operator>>(Istream& is, phasePairKey& key);
 
-        //- Write to stdout
+        //- Write to Ostream
         friend Ostream& operator<<(Ostream& os, const phasePairKey& key);
 };
 
diff --git a/applications/solvers/multiphase/twoPhaseEulerFoam/twoPhaseSystem/phasePair/phasePairKey/phasePairKey.C b/applications/solvers/multiphase/twoPhaseEulerFoam/twoPhaseSystem/phasePair/phasePairKey/phasePairKey.C
index b9bec10152..cf1097602e 100644
--- a/applications/solvers/multiphase/twoPhaseEulerFoam/twoPhaseSystem/phasePair/phasePairKey/phasePairKey.C
+++ b/applications/solvers/multiphase/twoPhaseEulerFoam/twoPhaseSystem/phasePair/phasePairKey/phasePairKey.C
@@ -39,6 +39,14 @@ Foam::phasePairKey::phasePairKey
 {}
 
 
+// * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //
+
+bool Foam::phasePairKey::ordered() const
+{
+    return ordered_;
+}
+
+
 // * * * * * * * * * * * * * * Member Operators  * * * * * * * * * * * * * * //
 
 Foam::label Foam::phasePairKey::hash::operator()
@@ -55,12 +63,8 @@ Foam::label Foam::phasePairKey::hash::operator()
                 word::hash()(key.second())
             );
     }
-    else
-    {
-        return
-            word::hash()(key.first())
-          + word::hash()(key.second());
-    }
+
+    return word::hash()(key.first()) + word::hash()(key.second());
 }
 
 
@@ -72,14 +76,13 @@ bool Foam::operator==
     const phasePairKey& b
 )
 {
-    const label cmp = Pair<word>::compare(a,b);
+    const auto cmp = Pair<word>::compare(a,b);
 
     return
+    (
         (a.ordered_ == b.ordered_)
-     && (
-            (a.ordered_ && (cmp == 1))
-         || (!a.ordered_ && (cmp != 0))
-        );
+     && (a.ordered_ ? (cmp == 1) : cmp)
+    );
 }
 
 
@@ -114,8 +117,8 @@ Foam::Istream& Foam::operator>>(Istream& is, phasePairKey& key)
         FatalErrorInFunction
             << "Phase pair type is not recognised. "
             << temp
-            << "Use (phaseDispersed in phaseContinuous) for an ordered"
-            << "pair, or (phase1 and pase2) for an unordered pair."
+            << "Use (phaseDispersed in phaseContinuous) for an ordered pair, "
+            << "or (phase1 and phase2) for an unordered pair."
             << exit(FatalError);
     }
 
diff --git a/applications/solvers/multiphase/twoPhaseEulerFoam/twoPhaseSystem/phasePair/phasePairKey/phasePairKey.H b/applications/solvers/multiphase/twoPhaseEulerFoam/twoPhaseSystem/phasePair/phasePairKey/phasePairKey.H
index eaa257df9f..6f9203b405 100644
--- a/applications/solvers/multiphase/twoPhaseEulerFoam/twoPhaseSystem/phasePair/phasePairKey/phasePairKey.H
+++ b/applications/solvers/multiphase/twoPhaseEulerFoam/twoPhaseSystem/phasePair/phasePairKey/phasePairKey.H
@@ -41,15 +41,13 @@ namespace Foam
 {
 
 // Forward declarations
-
 class phasePairKey;
 
-bool operator==(const phasePairKey&, const phasePairKey&);
-bool operator!=(const phasePairKey&, const phasePairKey&);
-
-Istream& operator>>(Istream&, phasePairKey&);
-Ostream& operator<<(Ostream&, const phasePairKey&);
+bool operator==(const phasePairKey& a, const phasePairKey& b);
+bool operator!=(const phasePairKey& a, const phasePairKey& b);
 
+Istream& operator>>(Istream& is, phasePairKey& key);
+Ostream& operator<<(Ostream& os, const phasePairKey& key);
 
 /*---------------------------------------------------------------------------*\
                          Class phasePairKey Declaration
@@ -66,9 +64,10 @@ class phasePairKey
 
 public:
 
+        //- Ordered or unordered hashing of word pair
         struct hash
         {
-            // Generate a hash from a phase pair key
+            //- Generate a hash from a phase pair key
             label operator()(const phasePairKey& key) const;
         };
 
@@ -78,31 +77,37 @@ public:
         //- Construct null
         phasePairKey() {} // = default
 
-        //- Construct from names and the ordering flag
+        //- Construct from names and optional ordering flag
         phasePairKey
         (
             const word& name1,
             const word& name2,
-            const bool ordered
+            const bool ordered = false
         );
 
 
-    // Destructor
+    //- Destructor
     virtual ~phasePairKey() = default;
 
 
+    // Access
+
+        //- Return the ordered flag
+        bool ordered() const;
+
+
     // Friend Operators
 
-        //- Test if keys are equal
+        //- Test for equality
         friend bool operator==(const phasePairKey& a, const phasePairKey& b);
 
-        //- Test if keys are unequal
+        //- Test for inequality
         friend bool operator!=(const phasePairKey& a, const phasePairKey& b);
 
-        //- Read from stdin
+        //- Read from Istream
         friend Istream& operator>>(Istream& is, phasePairKey& key);
 
-        //- Write to stdout
+        //- Write to Ostream
         friend Ostream& operator<<(Ostream& os, const phasePairKey& key);
 };