diff --git a/src/lagrangian/intermediate/Make/files b/src/lagrangian/intermediate/Make/files
index 4d6e12f6dc..445cbc2a20 100644
--- a/src/lagrangian/intermediate/Make/files
+++ b/src/lagrangian/intermediate/Make/files
@@ -120,7 +120,7 @@ phaseProperties/phasePropertiesList/phasePropertiesList.C
 
 /* additional helper classes */
 clouds/Templates/KinematicCloud/cloudSolution/cloudSolution.C
-
+submodels/CloudFunctionObjects/CloudFunctionObject/cloudFunctionObjectTools.C
 
 /* averaging methods */
 submodels/MPPIC/AveragingMethods/makeAveragingMethods.C
diff --git a/src/lagrangian/intermediate/parcels/include/makeParcelCloudFunctionObjects.H b/src/lagrangian/intermediate/parcels/include/makeParcelCloudFunctionObjects.H
index 6b0d78ac38..f2fc385cb6 100644
--- a/src/lagrangian/intermediate/parcels/include/makeParcelCloudFunctionObjects.H
+++ b/src/lagrangian/intermediate/parcels/include/makeParcelCloudFunctionObjects.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2018 OpenFOAM Foundation
-    Copyright (C) 2020-2022 OpenCFD Ltd.
+    Copyright (C) 2020-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -38,10 +38,10 @@ License
 #include "ParticleTracks.H"
 #include "ParticleTrap.H"
 #include "ParticleZoneInfo.H"
+#include "ParticleHistogram.H"
 #include "PatchCollisionDensity.H"
 #include "PatchInteractionFields.H"
 #include "PatchPostProcessing.H"
-#include "PatchParticleHistogram.H"
 #include "RemoveParcels.H"
 #include "VoidFraction.H"
 #include "KinematicReynoldsNumber.H"
@@ -60,10 +60,10 @@ License
     makeCloudFunctionObjectType(ParticleTracks, CloudType);                    \
     makeCloudFunctionObjectType(ParticleTrap, CloudType);                      \
     makeCloudFunctionObjectType(ParticleZoneInfo, CloudType);                  \
+    makeCloudFunctionObjectType(ParticleHistogram, CloudType);                 \
     makeCloudFunctionObjectType(PatchCollisionDensity, CloudType);             \
     makeCloudFunctionObjectType(PatchInteractionFields, CloudType);            \
     makeCloudFunctionObjectType(PatchPostProcessing, CloudType);               \
-    makeCloudFunctionObjectType(PatchParticleHistogram, CloudType);            \
     makeCloudFunctionObjectType(RemoveParcels, CloudType);                     \
     makeCloudFunctionObjectType(VoidFraction, CloudType);                      \
     makeCloudFunctionObjectType(KinematicReynoldsNumber, CloudType);           \
diff --git a/src/lagrangian/intermediate/parcels/include/makeReactingParcelCloudFunctionObjects.H b/src/lagrangian/intermediate/parcels/include/makeReactingParcelCloudFunctionObjects.H
index e8bed51a3e..e620ceb4c1 100644
--- a/src/lagrangian/intermediate/parcels/include/makeReactingParcelCloudFunctionObjects.H
+++ b/src/lagrangian/intermediate/parcels/include/makeReactingParcelCloudFunctionObjects.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2018 OpenFOAM Foundation
-    Copyright (C) 2020-2022 OpenCFD Ltd.
+    Copyright (C) 2020-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -38,10 +38,10 @@ License
 #include "ParticleTracks.H"
 #include "ParticleTrap.H"
 #include "ParticleZoneInfo.H"
+#include "ParticleHistogram.H"
 #include "PatchCollisionDensity.H"
 #include "PatchInteractionFields.H"
 #include "PatchPostProcessing.H"
-#include "PatchParticleHistogram.H"
 #include "RemoveParcels.H"
 #include "VoidFraction.H"
 #include "NusseltNumber.H"
@@ -63,10 +63,10 @@ License
     makeCloudFunctionObjectType(ParticleTracks, CloudType);                    \
     makeCloudFunctionObjectType(ParticleTrap, CloudType);                      \
     makeCloudFunctionObjectType(ParticleZoneInfo, CloudType);                  \
+    makeCloudFunctionObjectType(ParticleHistogram, CloudType);                 \
     makeCloudFunctionObjectType(PatchCollisionDensity, CloudType);             \
     makeCloudFunctionObjectType(PatchInteractionFields, CloudType);            \
     makeCloudFunctionObjectType(PatchPostProcessing, CloudType);               \
-    makeCloudFunctionObjectType(PatchParticleHistogram, CloudType);            \
     makeCloudFunctionObjectType(RemoveParcels, CloudType);                     \
     makeCloudFunctionObjectType(VoidFraction, CloudType);                      \
     makeCloudFunctionObjectType(NusseltNumber, CloudType);                     \
diff --git a/src/lagrangian/intermediate/parcels/include/makeThermoParcelCloudFunctionObjects.H b/src/lagrangian/intermediate/parcels/include/makeThermoParcelCloudFunctionObjects.H
index 0e0a312b8f..4a8a37f4fc 100644
--- a/src/lagrangian/intermediate/parcels/include/makeThermoParcelCloudFunctionObjects.H
+++ b/src/lagrangian/intermediate/parcels/include/makeThermoParcelCloudFunctionObjects.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021-2022 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -37,10 +37,10 @@ License
 #include "ParticleTracks.H"
 #include "ParticleTrap.H"
 #include "ParticleZoneInfo.H"
+#include "ParticleHistogram.H"
 #include "PatchCollisionDensity.H"
 #include "PatchInteractionFields.H"
 #include "PatchPostProcessing.H"
-#include "PatchParticleHistogram.H"
 #include "RemoveParcels.H"
 #include "VoidFraction.H"
 #include "NusseltNumber.H"
@@ -61,10 +61,10 @@ License
     makeCloudFunctionObjectType(ParticleTracks, CloudType);                    \
     makeCloudFunctionObjectType(ParticleTrap, CloudType);                      \
     makeCloudFunctionObjectType(ParticleZoneInfo, CloudType);                  \
+    makeCloudFunctionObjectType(ParticleHistogram, CloudType);                 \
     makeCloudFunctionObjectType(PatchCollisionDensity, CloudType);             \
     makeCloudFunctionObjectType(PatchInteractionFields, CloudType);            \
     makeCloudFunctionObjectType(PatchPostProcessing, CloudType);               \
-    makeCloudFunctionObjectType(PatchParticleHistogram, CloudType);            \
     makeCloudFunctionObjectType(RemoveParcels, CloudType);                     \
     makeCloudFunctionObjectType(VoidFraction, CloudType);                      \
     makeCloudFunctionObjectType(NusseltNumber, CloudType);                     \
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/CloudFunctionObject/cloudFunctionObjectTools.C b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/CloudFunctionObject/cloudFunctionObjectTools.C
new file mode 100644
index 0000000000..1f58610711
--- /dev/null
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/CloudFunctionObject/cloudFunctionObjectTools.C
@@ -0,0 +1,113 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2023 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+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 "cloudFunctionObjectTools.H"
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+Foam::cloudFunctionObjectTools::collector::collector
+(
+    const dictionary& dict,
+    const polyMesh& mesh
+)
+:
+    isPatch_(false),
+    IDs_(),
+    names_(),
+    BBs_()
+{
+    wordRes matcher;
+
+    if (dict.readIfPresent("patches", matcher) && !matcher.empty())
+    {
+        isPatch_ = true;
+
+        IDs_ = mesh.boundaryMesh().indices(matcher);
+
+        names_.resize(IDs_.size());
+
+        label count = 0;
+        for (const label patchi : IDs_)
+        {
+            names_[count] = mesh.boundaryMesh()[patchi].name();
+            ++count;
+        }
+    }
+    else if (dict.readIfPresent("faceZones", matcher))
+    {
+        const faceZoneMesh& fzm = mesh.faceZones();
+
+        IDs_ = fzm.indices(matcher);
+
+        BBs_.resize(IDs_.size());
+        names_.resize(IDs_.size());
+
+        label count = 0;
+        for (const label zonei : IDs_)
+        {
+            const faceZone& fz = fzm[zonei];
+            names_[count] = fz.name();
+
+            auto& bb = BBs_[count];
+            ++count;
+
+            bb.reset();
+
+            const auto& faces = mesh.faces();
+            const auto& points = mesh.points();
+            for (const label facei : fz)
+            {
+                bb.add(points, faces[facei]);
+            }
+            bb.reduce();
+            bb.inflate(0.05);
+        }
+    }
+
+    if (matcher.empty() || IDs_.size() < 1)
+    {
+        FatalIOErrorInFunction(dict)
+            << "No matching patches or face zones found: "
+            << flatOutput(matcher) << nl
+            << exit(FatalIOError);
+    }
+}
+
+
+Foam::cloudFunctionObjectTools::collector::collector
+(
+    const collector& phc
+)
+:
+    isPatch_(phc.isPatch_),
+    IDs_(phc.IDs_),
+    names_(phc.names_),
+    BBs_(phc.BBs_)
+{}
+
+
+// ************************************************************************* //
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/CloudFunctionObject/cloudFunctionObjectTools.H b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/CloudFunctionObject/cloudFunctionObjectTools.H
new file mode 100644
index 0000000000..e5fe1fee3e
--- /dev/null
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/CloudFunctionObject/cloudFunctionObjectTools.H
@@ -0,0 +1,129 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2023 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+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::cloudFunctionObjectTools::collector
+
+Description
+    Implementation of template-invariant tools for
+    various function objects such as Foam::ParticleHistogram.
+
+SourceFiles
+    cloudFunctionObjectTools.C
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef cloudFunctionObjectTools_collector_H
+#define cloudFunctionObjectTools_collector_H
+
+#include "polyMesh.H"
+#include "boundBox.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+/*---------------------------------------------------------------------------*\
+                Namespace cloudFunctionObjectTools Declaration
+\*---------------------------------------------------------------------------*/
+
+namespace cloudFunctionObjectTools
+{
+
+/*---------------------------------------------------------------------------*\
+                        Class collector Declaration
+\*---------------------------------------------------------------------------*/
+
+class collector
+{
+    // Private Data
+
+        //- Flag to decide if the collector is patch based
+        bool isPatch_;
+
+        //- List of indices of collectors (zones or patches)
+        labelList IDs_;
+
+        //- List of names of collectors
+        wordList names_;
+
+        //- List of bounding-boxes of collectors
+        List<boundBox> BBs_;
+
+
+public:
+
+    // Constructors
+
+        //- Construct from dictionary
+        collector
+        (
+            const dictionary& dict,
+            const polyMesh& mesh
+        );
+
+        //- Copy construct
+        collector(const collector& phc);
+
+        //- No copy assignment
+        void operator=(const collector&) = delete;
+
+
+    //- Destructor
+    virtual ~collector() = default;
+
+
+    // Member Functions
+
+    // Access
+
+        //- Return the flag if the collector is patch based
+        bool isPatch() const noexcept { return isPatch_; }
+
+        //- Return number of collectors (zones or patches)
+        label size() const noexcept { return IDs_.size(); }
+
+        //- Return const reference to the indices of collectors
+        const labelList& IDs() const noexcept { return IDs_; }
+
+        //- Return const reference to the names of collectors
+        const wordList& names() const noexcept { return names_; }
+
+        //- Return const reference to the bounding-boxes of collectors
+        const List<boundBox>& BBs() const noexcept { return BBs_; }
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace cloudFunctionObjectTools
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ParticleHistogram/ParticleHistogram.C b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ParticleHistogram/ParticleHistogram.C
new file mode 100644
index 0000000000..e0010d085b
--- /dev/null
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ParticleHistogram/ParticleHistogram.C
@@ -0,0 +1,278 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2020-2023 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+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 "ParticleHistogram.H"
+#include "Pstream.H"
+#include "stringListOps.H"
+#include "ListOps.H"
+#include "ListListOps.H"
+
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
+
+template<class CloudType>
+void Foam::ParticleHistogram<CloudType>::writeFileHeader(Ostream& os) const
+{
+    this->writeHeaderValue(os, "nBin", nBins_);
+    this->writeHeaderValue(os, "min", range_.min());
+    this->writeHeaderValue(os, "max", range_.max());
+    this->writeHeader(os, "");
+    this->writeCommented(os, "dEdge1");
+    os  << tab << "dEdge2"
+        << tab << "nParticles"
+        << tab << "nParticlesCumulative"
+        << endl;
+}
+
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+template<class CloudType>
+Foam::ParticleHistogram<CloudType>::ParticleHistogram
+(
+    const dictionary& dict,
+    CloudType& owner,
+    const word& modelName
+)
+:
+    CloudFunctionObject<CloudType>(dict, owner, modelName, typeName),
+    functionObjects::writeFile
+    (
+        owner,
+        this->localPath(),
+        typeName
+    ),
+    collector_(this->coeffDict(), owner.mesh()),
+    nBins_
+    (
+        this->coeffDict().template getCheck<label>("nBins", labelMinMax::ge(1))
+    ),
+    maxStoredParcels_(this->coeffDict().getScalar("maxStoredParcels")),
+    range_
+    (
+        this->coeffDict().getScalar("min"),
+        this->coeffDict().getScalar("max")
+    ),
+    binEdges_(nBins_ + 1),
+    nParticlesCumulative_(),
+    dParticles_(),
+    nParticles_()
+{
+    writeFile::read(this->coeffDict());
+
+    if (!range_.good())
+    {
+        FatalIOErrorInFunction(this->coeffDict())
+            << "Invalid histogram range: " << range_
+            << exit(FatalIOError);
+    }
+
+    if (maxStoredParcels_ <= 0)
+    {
+        FatalIOErrorInFunction(this->coeffDict())
+            << "maxStoredParcels = " << maxStoredParcels_
+            << ", cannot be equal to or less than zero"
+            << exit(FatalIOError);
+    }
+
+    // Compute histogram-bin properties
+    binEdges_[0] = range_.min();
+    const scalar delta = range_.span()/scalar(nBins_);
+    for (label i = 0; i < nBins_; ++i)
+    {
+        const scalar next = range_.min() + (i+1)*delta;
+        binEdges_[i+1] = next;
+    }
+
+    const label sz = collector_.size();
+    nParticlesCumulative_ = List<scalarList>(sz, scalarList(nBins_, Zero));
+    dParticles_.resize(sz);
+    nParticles_.resize(sz);
+}
+
+
+template<class CloudType>
+Foam::ParticleHistogram<CloudType>::ParticleHistogram
+(
+    const ParticleHistogram<CloudType>& ph
+)
+:
+    CloudFunctionObject<CloudType>(ph),
+    writeFile(ph),
+    collector_(ph.collector_),
+    nBins_(ph.nBins_),
+    maxStoredParcels_(ph.maxStoredParcels_),
+    range_(ph.range_),
+    binEdges_(ph.binEdges_),
+    nParticlesCumulative_(ph.nParticlesCumulative_),
+    dParticles_(ph.dParticles_),
+    nParticles_(ph.nParticles_)
+{}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+template<class CloudType>
+void Foam::ParticleHistogram<CloudType>::postPatch
+(
+    const parcelType& p,
+    const polyPatch& pp,
+    bool&
+)
+{
+    if (!collector_.isPatch())
+    {
+        return;
+    }
+
+    const label patchi = pp.index();
+    const label localPatchi = collector_.IDs().find(patchi);
+
+    if
+    (
+        localPatchi != -1
+     && dParticles_[localPatchi].size() < maxStoredParcels_
+    )
+    {
+        dParticles_[localPatchi].append(p.d());
+        nParticles_[localPatchi].append(p.nParticle());
+    }
+}
+
+
+template<class CloudType>
+void Foam::ParticleHistogram<CloudType>::postFace
+(
+    const parcelType& p,
+    bool&
+)
+{
+    if (collector_.isPatch())
+    {
+        return;
+    }
+
+    const labelList& IDs = collector_.IDs();
+    const List<boundBox>& BBs = collector_.BBs();
+    const faceZoneMesh& fzm = this->owner().mesh().faceZones();
+
+    forAll(IDs, i)
+    {
+        if (!BBs[i].contains(p.position()))
+        {
+            // Quick reject if the particle is not in the face zone bound box
+            continue;
+        }
+
+        const label zonei = IDs[i];
+        const label localFacei = fzm[zonei].find(p.face());
+
+        if
+        (
+            localFacei != -1
+         && dParticles_[i].size() < maxStoredParcels_
+        )
+        {
+            dParticles_[i].append(p.d());
+            nParticles_[i].append(p.nParticle());
+        }
+    }
+}
+
+
+template<class CloudType>
+void Foam::ParticleHistogram<CloudType>::write()
+{
+    const wordList& names = collector_.names();
+
+    forAll(names, i)
+    {
+        List<scalarList> procDiameters(Pstream::nProcs());
+        procDiameters[Pstream::myProcNo()] = dParticles_[i];
+        Pstream::gatherList(procDiameters);
+
+        List<scalarList> procParticles(Pstream::nProcs());
+        procParticles[Pstream::myProcNo()] = nParticles_[i];
+        Pstream::gatherList(procParticles);
+
+        if (Pstream::master())
+        {
+            scalarList globalDiameters;
+            globalDiameters = ListListOps::combine<scalarList>
+            (
+                procDiameters,
+                accessOp<scalarList>()
+            );
+
+            scalarList globalParticles;
+            globalParticles = ListListOps::combine<scalarList>
+            (
+                procParticles,
+                accessOp<scalarList>()
+            );
+
+            // Compute histogram
+            scalarList nParticles(nBins_, Zero);
+            const scalar delta = range_.span()/scalar(nBins_);
+            forAll(globalDiameters, j)
+            {
+                const label bini = (globalDiameters[j] - range_.min())/delta;
+                if (bini >= 0 && bini < nBins_)
+                {
+                    nParticles[bini] += globalParticles[j];
+                    nParticlesCumulative_[i][bini] += globalParticles[j];
+                }
+            }
+
+            if (this->writeToFile())
+            {
+                autoPtr<OFstream> osPtr = this->newFileAtTime
+                (
+                    names[i],
+                    this->owner().time().value()
+                );
+                OFstream& os = osPtr.ref();
+
+                writeFileHeader(os);
+
+                forAll(nParticles, j)
+                {
+                    os  << binEdges_[j] << tab
+                        << binEdges_[j + 1] << tab
+                        << nParticles[j] << tab
+                        << nParticlesCumulative_[i][j]
+                        << nl;
+                }
+            }
+        }
+
+        dParticles_[i].clearStorage();
+        nParticles_[i].clearStorage();
+    }
+}
+
+
+// ************************************************************************* //
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchParticleHistogram/PatchParticleHistogram.H b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ParticleHistogram/ParticleHistogram.H
similarity index 55%
rename from src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchParticleHistogram/PatchParticleHistogram.H
rename to src/lagrangian/intermediate/submodels/CloudFunctionObjects/ParticleHistogram/ParticleHistogram.H
index c8b3b99239..6b2866fd40 100644
--- a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchParticleHistogram/PatchParticleHistogram.H
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ParticleHistogram/ParticleHistogram.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2020 OpenCFD Ltd.
+    Copyright (C) 2020-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -24,64 +24,86 @@ License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
 Class
-    Foam::PatchParticleHistogram
+    Foam::ParticleHistogram
 
 Description
     Computes a histogram for the distribution of particle diameters
-    and corresponding number of particles hitting on a given list of patches.
+    and corresponding number of particles hitting on a given list of
+    patches or face zones.
 
     Operands:
     \table
       Operand        | Type | Location
       input          | -    | -
-      output file    | dat  | $FOAM_CASE/postProcessing/\<FO\>/\<time\>/\<file\>
+      output file    | dat  | \<case\>/postProcessing/\<FO\>/\<time\>/\<file\>
       output field   | -    | -
     \endtable
 
-    The output file contains two columns, the first is the bin edges of
-    the particle diameter (i.e. \c d), and the second is the number of
-    particles whose diameter falling into the corresponding bin
-    (i.e. \c nParticles).
+    The output file contains four columns, from the first to the last:
+    \vartable
+        dEdge1      | Left bin-edge of particle diameter
+        dEdge2      | Right bin-edge of particle diameter
+        nParticles  | Number of particles falling into the corresponding bin
+        nParticlesCumulative | Cumulative number of binned particles
+    \endvartable
 
 Usage
     Minimal example by using
     \c constant/reactingCloud1Properties.cloudFunctions:
     \verbatim
-    patchParticleHistogram1
+    particleHistogram1
     {
-        // Mandatory entries (unmodifiable)
-        type             patchParticleHistogram;
-        patches          (<patch1> <patch2> ... <patchN>);
-        nBins            10;
-        min              0.1;
-        max              10.0;
-        maxStoredParcels 20;
+        // Mandatory entries
+        type                 particleHistogram;
+        nBins                <label>;
+        min                  <scalar>;
+        max                  <scalar>;
+        maxStoredParcels     <scalar>;
+
+        // Conditional entries
+
+            // Option-1
+            patches          (<wordRes>);
+
+            // Option-2
+            faceZones        (<wordRes>);
+
+        // Inherited entries
+        ...
     }
     \endverbatim
 
     where the entries mean:
     \table
-      Property     | Description                        | Type   | Reqd  | Dflt
-      type         | Type name: patchParticleHistogram  | word   |  yes  | -
-      patches      | Names of operand patches         | wordList |  yes  | -
+      Property     | Description                        | Type   | Reqd  | Deflt
+      type         | Type name: particleHistogram       | word   |  yes  | -
       nBins        | Number of histogram bins           | label  |  yes  | -
       max          | Maximum value of histogram data    | scalar |  yes  | -
       min          | Minimum value of histogram data    | scalar |  yes  | -
       maxStoredParcels | Maximum number of parcels to process | label | yes | -
+      patches      | Names of operand patches          | wordRes |  choice  | -
+      faceZones    | Names of operand face zones       | wordRes |  choice  | -
     \endtable
 
+    The inherited entries are elaborated in:
+      - \link CloudFunctionObject.H \endlink
+      - \link writeFile.H \endlink
+
 Note
   - The underlying type of \c maxStoredParcels is set as a scalar for I/O.
 
 SourceFiles
-    PatchParticleHistogram.C
+    ParticleHistogram.C
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef PatchParticleHistogram_H
-#define PatchParticleHistogram_H
+#ifndef Foam_ParticleHistogram_H
+#define Foam_ParticleHistogram_H
 
 #include "CloudFunctionObject.H"
+#include "writeFile.H"
+#include "MinMax.H"
+#include "cloudFunctionObjectTools.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -89,81 +111,64 @@ namespace Foam
 {
 
 /*---------------------------------------------------------------------------*\
-                    Class PatchParticleHistogram Declaration
+                    Class ParticleHistogram Declaration
 \*---------------------------------------------------------------------------*/
 
 template<class CloudType>
-class PatchParticleHistogram
+class ParticleHistogram
 :
-    public CloudFunctionObject<CloudType>
+    public CloudFunctionObject<CloudType>,
+    public functionObjects::writeFile
 {
     // Private Data
 
-        //- Convenience typedef for parcel type
-        typedef typename CloudType::particleType parcelType;
+        // Typedefs
+
+            //- Convenience typedef for parcel type
+            typedef typename CloudType::particleType parcelType;
+
+        //- Collector surfaces
+        cloudFunctionObjectTools::collector collector_;
 
         //- Number of data bins
         const label nBins_;
 
-        //- Minimum value of histogram data
-        const scalar min_;
-
-        //- Maximum value of histogram data
-        const scalar max_;
-
-        //- Bin width of histogram
-        const scalar delta_;
-
         //- Maximum number of parcels to store - set as a scalar for I/O
         const scalar maxStoredParcels_;
 
+        //- Min/Max value of histogram data
+        const scalarMinMax range_;
+
         //- Bin edges of histogram
         scalarField binEdges_;
 
-        //- List of patch indices to post-process
-        labelList patchIDs_;
-
-        //- Accumulated number of particles per patch
+        //- Accumulated number of particles per surface
         //- binned according to the histogram settings
-        List<List<scalar>> nParticlesCumulative_;
+        List<scalarList> nParticlesCumulative_;
 
-        //- List of time for each data record
-        List<DynamicList<scalar>> times_;
+        // List of surface-hit particle diameters
+        List<DynamicList<scalar>> dParticles_;
 
-        // List of patch-hit particle diameters
-        List<DynamicList<scalar>> patchDiameters_;
-
-        // List of number of patch-hit particles
-        List<DynamicList<scalar>> patchParticles_;
+        // List of number of surface-hit particles
+        List<DynamicList<scalar>> nParticles_;
 
 
     // Private Member Functions
 
-        //- Return local patchi if patch is in patchIds_ list
-        label applyToPatch(const label globalPatchi) const;
-
-
-protected:
-
-    // Protected Member Functions
-
-        //- Write post-processing info
-        void write();
+        //- Write output file header
+        void writeFileHeader(Ostream& os) const;
 
 
 public:
 
     //- Runtime type information
-    TypeName("patchParticleHistogram");
+    TypeName("particleHistogram");
 
 
     // Constructors
 
-        //- No default construct
-        PatchParticleHistogram() = delete;
-
         //- Construct from dictionary
-        PatchParticleHistogram
+        ParticleHistogram
         (
             const dictionary& dict,
             CloudType& owner,
@@ -171,36 +176,45 @@ public:
         );
 
         //- Copy construct
-        PatchParticleHistogram(const PatchParticleHistogram<CloudType>& ppm);
+        ParticleHistogram(const ParticleHistogram<CloudType>& ph);
 
         //- No copy assignment
-        void operator=(const PatchParticleHistogram<CloudType>&) = delete;
+        void operator=(const ParticleHistogram<CloudType>&) = delete;
 
         //- Construct and return a clone
         virtual autoPtr<CloudFunctionObject<CloudType>> clone() const
         {
             return autoPtr<CloudFunctionObject<CloudType>>
             (
-                new PatchParticleHistogram<CloudType>(*this)
+                new ParticleHistogram<CloudType>(*this)
             );
         }
 
 
     //- Destructor
-    virtual ~PatchParticleHistogram() = default;
+    virtual ~ParticleHistogram() = default;
 
 
     // Member Functions
 
-        // Evaluation
+    // Evaluation
 
-            //- Post-patch hook
-            virtual void postPatch
-            (
-                const parcelType& p,
-                const polyPatch& pp,
-                bool& keepParticle
-            );
+        //- Post-patch hook
+        virtual void postPatch
+        (
+            const parcelType& p,
+            const polyPatch& pp,
+            bool& keepParticle
+        );
+
+        //- Post-face hook
+        virtual void postFace(const parcelType& p, bool& keepParticle);
+
+
+    // I-O
+
+        //- Write post-processing info
+        virtual void write();
 };
 
 
@@ -212,7 +226,7 @@ public:
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 #ifdef NoRepository
-    #include "PatchParticleHistogram.C"
+    #include "ParticleHistogram.C"
 #endif
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchParticleHistogram/PatchParticleHistogram.C b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchParticleHistogram/PatchParticleHistogram.C
deleted file mode 100644
index 43b04a80c0..0000000000
--- a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/PatchParticleHistogram/PatchParticleHistogram.C
+++ /dev/null
@@ -1,253 +0,0 @@
-/*---------------------------------------------------------------------------*\
-  =========                 |
-  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
-   \\    /   O peration     |
-    \\  /    A nd           | www.openfoam.com
-     \\/     M anipulation  |
--------------------------------------------------------------------------------
-    Copyright (C) 2020-2021 OpenCFD Ltd.
--------------------------------------------------------------------------------
-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 "PatchParticleHistogram.H"
-#include "Pstream.H"
-#include "stringListOps.H"
-#include "ListOps.H"
-#include "ListListOps.H"
-
-// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
-
-template<class CloudType>
-Foam::label Foam::PatchParticleHistogram<CloudType>::applyToPatch
-(
-    const label globalPatchi
-) const
-{
-    return patchIDs_.find(globalPatchi);
-}
-
-
-// * * * * * * * * * * * * * protected Member Functions  * * * * * * * * * * //
-
-template<class CloudType>
-void Foam::PatchParticleHistogram<CloudType>::write()
-{
-    forAll(times_, i)
-    {
-        List<List<scalar>> procTimes(Pstream::nProcs());
-        procTimes[Pstream::myProcNo()] = times_[i];
-        Pstream::gatherList(procTimes);
-
-        List<List<scalar>> procDiameters(Pstream::nProcs());
-        procDiameters[Pstream::myProcNo()] = patchDiameters_[i];
-        Pstream::gatherList(procDiameters);
-
-        List<List<scalar>> procParticles(Pstream::nProcs());
-        procParticles[Pstream::myProcNo()] = patchParticles_[i];
-        Pstream::gatherList(procParticles);
-
-        if (Pstream::master())
-        {
-            const fvMesh& mesh = this->owner().mesh();
-
-            mkDir(this->writeTimeDir());
-
-            const word& patchName = mesh.boundaryMesh()[patchIDs_[i]].name();
-
-            OFstream patchOutFile
-            (
-                this->writeTimeDir()/patchName + ".post",
-                IOstreamOption::ASCII,
-                mesh.time().writeCompression()
-            );
-
-            List<scalar> globalTimes;
-            globalTimes = ListListOps::combine<List<scalar>>
-            (
-                procTimes,
-                accessOp<List<scalar>>()
-            );
-
-            List<scalar> globalDiameters;
-            globalDiameters = ListListOps::combine<List<scalar>>
-            (
-                procDiameters,
-                accessOp<List<scalar>>()
-            );
-
-            List<scalar> globalParticles;
-            globalParticles = ListListOps::combine<List<scalar>>
-            (
-                procParticles,
-                accessOp<List<scalar>>()
-            );
-
-            // Compute histogram
-            List<scalar> nParticles(nBins_, Zero);
-            forAll(globalDiameters, j)
-            {
-                const label bini = (globalDiameters[j] - min_)/delta_;
-                if (bini >= 0 && bini < nBins_)
-                {
-                    nParticles[bini] += globalParticles[j];
-                    nParticlesCumulative_[i][bini] += globalParticles[j];
-                }
-            }
-
-            patchOutFile
-                << "# nBin=" << nBins_
-                << "; min="  << min_
-                << "; max="  << max_ << nl
-                << "# dEdge1    dEdge2    nParticles    nParticlesCumulative"
-                << endl;
-
-            forAll(nParticles, j)
-            {
-                patchOutFile
-                    << binEdges_[j]
-                    << ' '
-                    << binEdges_[j + 1]
-                    << ' '
-                    << nParticles[j]
-                    << ' '
-                    << nParticlesCumulative_[i][j]
-                    << nl;
-            }
-        }
-
-        times_[i].clearStorage();
-        patchDiameters_[i].clearStorage();
-        patchParticles_[i].clearStorage();
-    }
-}
-
-
-// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
-
-template<class CloudType>
-Foam::PatchParticleHistogram<CloudType>::PatchParticleHistogram
-(
-    const dictionary& dict,
-    CloudType& owner,
-    const word& modelName
-)
-:
-    CloudFunctionObject<CloudType>(dict, owner, modelName, typeName),
-    nBins_(dict.getCheck<label>("nBins", labelMinMax::ge(1))),
-    min_(dict.getScalar("min")),
-    max_(dict.getScalar("max")),
-    delta_((max_ - min_)/scalar(nBins_)),
-    maxStoredParcels_(dict.getScalar("maxStoredParcels")),
-    binEdges_(nBins_ + 1),
-    patchIDs_(),
-    nParticlesCumulative_(),
-    times_(),
-    patchDiameters_(),
-    patchParticles_()
-{
-    if (min_ >= max_)
-    {
-        FatalIOErrorInFunction(dict)
-            << "Histogram minimum = " << min_
-            << ", cannot be larger than histogram maximum = " << max_
-            << exit(FatalIOError);
-    }
-
-    if (maxStoredParcels_ <= 0)
-    {
-        FatalIOErrorInFunction(dict)
-            << "maxStoredParcels = " << maxStoredParcels_
-            << ", cannot be equal to or less than zero"
-            << exit(FatalIOError);
-    }
-
-    // Compute histogram-bin properties
-    binEdges_[0] = min_;
-    for (label i = 0; i < nBins_; ++i)
-    {
-        const scalar next = min_ + (i+1)*delta_;
-        binEdges_[i+1] = next;
-    }
-
-    // Compute histogram-patch properties
-    const wordRes patchMatcher(dict.get<wordRes>("patches"));
-
-    patchIDs_ = patchMatcher.matching(owner.mesh().boundaryMesh().names());
-
-    if (patchIDs_.empty())
-    {
-        FatalIOErrorInFunction(dict)
-            << "No matching patches found: "
-            << flatOutput(patchMatcher) << nl
-            << exit(FatalIOError);
-    }
-
-    nParticlesCumulative_ =
-        List<List<scalar>>(patchIDs_.size(), List<scalar>(nBins_, Zero));
-
-    times_.setSize(patchIDs_.size());
-    patchDiameters_.setSize(patchIDs_.size());
-    patchParticles_.setSize(patchIDs_.size());
-}
-
-
-template<class CloudType>
-Foam::PatchParticleHistogram<CloudType>::PatchParticleHistogram
-(
-    const PatchParticleHistogram<CloudType>& ppm
-)
-:
-    CloudFunctionObject<CloudType>(ppm),
-    nBins_(ppm.nBins_),
-    min_(ppm.min_),
-    max_(ppm.max_),
-    delta_(ppm.delta_),
-    maxStoredParcels_(ppm.maxStoredParcels_),
-    binEdges_(ppm.binEdges_),
-    patchIDs_(ppm.patchIDs_),
-    nParticlesCumulative_(ppm.nParticlesCumulative_),
-    times_(ppm.times_),
-    patchDiameters_(ppm.patchDiameters_),
-    patchParticles_(ppm.patchParticles_)
-{}
-
-
-// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
-
-template<class CloudType>
-void Foam::PatchParticleHistogram<CloudType>::postPatch
-(
-    const parcelType& p,
-    const polyPatch& pp,
-    bool&
-)
-{
-    const label patchi = pp.index();
-    const label localPatchi = applyToPatch(patchi);
-
-    if (localPatchi != -1 && times_[localPatchi].size() < maxStoredParcels_)
-    {
-        times_[localPatchi].append(this->owner().time().value());
-        patchDiameters_[localPatchi].append(p.d());
-        patchParticles_[localPatchi].append(p.nParticle());
-    }
-}
-
-
-// ************************************************************************* //
diff --git a/tutorials/lagrangian/reactingParcelFoam/airRecirculationRoom/transient/constant/reactingCloud1Properties b/tutorials/lagrangian/reactingParcelFoam/airRecirculationRoom/transient/constant/reactingCloud1Properties
index 2222916d68..9dfedc27c4 100644
--- a/tutorials/lagrangian/reactingParcelFoam/airRecirculationRoom/transient/constant/reactingCloud1Properties
+++ b/tutorials/lagrangian/reactingParcelFoam/airRecirculationRoom/transient/constant/reactingCloud1Properties
@@ -531,7 +531,7 @@ in the injection models set above we have
 36  μm ->  2 parcels per second
 45  μm ->  2 parcels per second
 
-therefore in the following "patchParticleHistogram1" we can set
+therefore in the following "particleHistogram1" we can set
     nBins = 9
     min = 0μm
     max = 45μm
@@ -547,9 +547,9 @@ in this ways the particles hitting the patches will be classified in the followi
     9) 40.01μm to 45.01μm <- the 45μm particles will be counted in this range
 */
 
-    patchParticleHistogram1
+    particleHistogram1
     {
-        type            patchParticleHistogram;
+        type            particleHistogram;
         patches
         (
             roof
diff --git a/tutorials/lagrangian/reactingParcelFoam/filter/constant/reactingCloud1Properties b/tutorials/lagrangian/reactingParcelFoam/filter/constant/reactingCloud1Properties
index 661e3e1d16..569edc4ee5 100644
--- a/tutorials/lagrangian/reactingParcelFoam/filter/constant/reactingCloud1Properties
+++ b/tutorials/lagrangian/reactingParcelFoam/filter/constant/reactingCloud1Properties
@@ -167,9 +167,9 @@ cloudFunctions
         writer          vtk;
     }
 
-    patchParticleHistogram1
+    particleHistogram1
     {
-        type            patchParticleHistogram;
+        type            particleHistogram;
         patches
         (
             cycLeft_half0