diff --git a/src/lagrangian/intermediate/parcels/include/makeParcelCloudFunctionObjects.H b/src/lagrangian/intermediate/parcels/include/makeParcelCloudFunctionObjects.H
index e56970999c..69618baabf 100644
--- a/src/lagrangian/intermediate/parcels/include/makeParcelCloudFunctionObjects.H
+++ b/src/lagrangian/intermediate/parcels/include/makeParcelCloudFunctionObjects.H
@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2018 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -34,6 +34,7 @@ License
 #include "ParticleErosion.H"
 #include "ParticleTracks.H"
 #include "ParticleTrap.H"
+#include "PatchCollisionDensity.H"
 #include "PatchPostProcessing.H"
 #include "VoidFraction.H"
 
@@ -48,6 +49,7 @@ License
     makeCloudFunctionObjectType(ParticleErosion, CloudType);                   \
     makeCloudFunctionObjectType(ParticleTracks, CloudType);                    \
     makeCloudFunctionObjectType(ParticleTrap, CloudType);                      \
+    makeCloudFunctionObjectType(PatchCollisionDensity, CloudType);             \
     makeCloudFunctionObjectType(PatchPostProcessing, CloudType);               \
     makeCloudFunctionObjectType(VoidFraction, CloudType);
 
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchCollisionDensity/PatchCollisionDensity.C b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchCollisionDensity/PatchCollisionDensity.C
new file mode 100644
index 0000000000..111ffcbedf
--- /dev/null
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchCollisionDensity/PatchCollisionDensity.C
@@ -0,0 +1,168 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2018 OpenFOAM Foundation
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "PatchCollisionDensity.H"
+#include "Pstream.H"
+#include "stringListOps.H"
+#include "ListOps.H"
+#include "ListListOps.H"
+
+// * * * * * * * * * * * * * Protected Member Functions  * * * * * * * * * * //
+
+template<class CloudType>
+void Foam::PatchCollisionDensity<CloudType>::write()
+{
+    const scalarField z(this->owner().mesh().nCells(), 0);
+
+    volScalarField
+    (
+        IOobject
+        (
+            this->owner().name() + ":collisionDensity",
+            this->owner().mesh().time().timeName(),
+            this->owner().mesh()
+        ),
+        this->owner().mesh(),
+        dimless/dimArea,
+        z,
+        collisionDensity_
+    )
+   .write();
+
+    volScalarField
+    (
+        IOobject
+        (
+            this->owner().name() + ":collisionDensityRate",
+            this->owner().mesh().time().timeName(),
+            this->owner().mesh()
+        ),
+        this->owner().mesh(),
+        dimless/dimArea/dimTime,
+        z,
+        (collisionDensity_ - collisionDensity0_)
+       /(this->owner().mesh().time().value() - time0_)
+    )
+   .write();
+
+    collisionDensity0_ == collisionDensity_;
+    time0_ = this->owner().mesh().time().value();
+}
+
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+template<class CloudType>
+Foam::PatchCollisionDensity<CloudType>::PatchCollisionDensity
+(
+    const dictionary& dict,
+    CloudType& owner,
+    const word& modelName
+)
+:
+    CloudFunctionObject<CloudType>(dict, owner, modelName, typeName),
+    minSpeed_(dict.lookupOrDefault<scalar>("minSpeed", -1)),
+    collisionDensity_
+    (
+        this->owner().mesh().boundary(),
+        volScalarField::Internal::null(),
+        calculatedFvPatchField<scalar>::typeName
+    ),
+    collisionDensity0_
+    (
+        this->owner().mesh().boundary(),
+        volScalarField::Internal::null(),
+        calculatedFvPatchField<scalar>::typeName
+    ),
+    time0_(this->owner().mesh().time().value())
+{
+    collisionDensity_ == 0;
+    collisionDensity0_ == 0;
+
+    IOobject io
+    (
+        this->owner().name() + ":collisionDensity",
+        this->owner().mesh().time().timeName(),
+        this->owner().mesh(),
+        IOobject::MUST_READ,
+        IOobject::NO_WRITE
+    );
+
+    if (io.typeHeaderOk<volScalarField>())
+    {
+        const volScalarField collisionDensity(io, this->owner().mesh());
+        collisionDensity_ == collisionDensity.boundaryField();
+        collisionDensity0_ == collisionDensity.boundaryField();
+    }
+}
+
+
+template<class CloudType>
+Foam::PatchCollisionDensity<CloudType>::PatchCollisionDensity
+(
+    const PatchCollisionDensity<CloudType>& ppm
+)
+:
+    CloudFunctionObject<CloudType>(ppm),
+    minSpeed_(ppm.minSpeed_),
+    collisionDensity_(ppm.collisionDensity_),
+    collisionDensity0_(ppm.collisionDensity0_),
+    time0_(ppm.time0_)
+{}
+
+
+// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
+
+template<class CloudType>
+Foam::PatchCollisionDensity<CloudType>::~PatchCollisionDensity()
+{}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+template<class CloudType>
+void Foam::PatchCollisionDensity<CloudType>::postPatch
+(
+    const parcelType& p,
+    const polyPatch& pp,
+    bool&
+)
+{
+    const label patchi = pp.index();
+    const label patchFacei = p.face() - pp.start();
+
+    vector nw, Up;
+    this->owner().patchData(p, pp, nw, Up);
+
+    const scalar speed = (p.U() - Up) & nw;
+    if (speed > minSpeed_)
+    {
+        collisionDensity_[patchi][patchFacei] +=
+            1/this->owner().mesh().magSf().boundaryField()[patchi][patchFacei];
+    }
+}
+
+
+// ************************************************************************* //
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchCollisionDensity/PatchCollisionDensity.H b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchCollisionDensity/PatchCollisionDensity.H
new file mode 100644
index 0000000000..8cb4d76bb4
--- /dev/null
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchCollisionDensity/PatchCollisionDensity.H
@@ -0,0 +1,152 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2018 OpenFOAM Foundation
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Class
+    Foam::PatchCollisionDensity
+
+Description
+    Function object which generates fields of the number and rate of collisions
+    per unit area on all patches. Can optionally take a minimum speed below
+    which a collision is not counted.
+
+    Example usage:
+    \verbatim
+    patchCollisionDensity1
+    {
+        type        patchCollisionDensity;
+        minSpeed    1e-3;
+    }
+    \endverbatim
+
+SourceFiles
+    PatchCollisionDensity.C
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef PatchCollisionDensity_H
+#define PatchCollisionDensity_H
+
+#include "CloudFunctionObject.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+/*---------------------------------------------------------------------------*\
+                    Class PatchCollisionDensity Declaration
+\*---------------------------------------------------------------------------*/
+
+template<class CloudType>
+class PatchCollisionDensity
+:
+    public CloudFunctionObject<CloudType>
+{
+    // Private data
+
+        typedef typename CloudType::particleType parcelType;
+
+        //- The threshold for a collision
+        const scalar minSpeed_;
+
+        //- The field of the number of collisions per unit area
+        volScalarField::Boundary collisionDensity_;
+
+        //- The field of the number of collisions per unit area at the last
+        //  output
+        volScalarField::Boundary collisionDensity0_;
+
+        //- The time at the last output
+        scalar time0_;
+
+
+protected:
+
+    // Protected Member Functions
+
+        //- Write post-processing info
+        void write();
+
+
+public:
+
+    //- Runtime type information
+    TypeName("patchCollisionDensity");
+
+
+    // Constructors
+
+        //- Construct from dictionary
+        PatchCollisionDensity
+        (
+            const dictionary& dict,
+            CloudType& owner,
+            const word& modelName
+        );
+
+        //- Construct copy
+        PatchCollisionDensity(const PatchCollisionDensity<CloudType>& ppm);
+
+        //- Construct and return a clone
+        virtual autoPtr<CloudFunctionObject<CloudType>> clone() const
+        {
+            return autoPtr<CloudFunctionObject<CloudType>>
+            (
+                new PatchCollisionDensity<CloudType>(*this)
+            );
+        }
+
+
+    //- Destructor
+    virtual ~PatchCollisionDensity();
+
+
+    // Member Functions
+
+        // Evaluation
+
+            //- Post-patch hook
+            virtual void postPatch
+            (
+                const parcelType& p,
+                const polyPatch& pp,
+                bool& keepParticle
+            );
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#ifdef NoRepository
+    #include "PatchCollisionDensity.C"
+#endif
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //