We have performed high-resolution direct numerical

simulation of microscale flows in both synthetic

representations of felt and geometries obtained from 3D

tomography of industrial felts. Preliminary data shows that• Pressure drop in felt is nonlinear and thus constant permeability

assumption does not hold for continuum models;

• Fully resolved simulation of single phase flow in uncompressed

and compressed pore scale geometries obtained from image

data is useful in obtaining permeability to porosity relationships

that can be used to parameter fit continuum models;

• Diffusive front tracking of two phases has been demonstrated

and can be extended to track sharp interfaces between multiple

fluids and triple point contact angles.

Development of an integrated modeling framework for simulating

water removal at the press section in paper making

Project objective

Yue Hao (LLNL), David Trebotich (LBNL), Wei Wang (LLNL),Jun Xu and David Turpin (Agenda 2020)

Lawrence Livermore National Laboratory / Lawrence Berkeley National Laboratory / Agenda 2020

Technical approach

Summary

Integrated modeling framework for

dewatering/rewet simulation

Direct simulation of pore-scale

flow in porous paper/felts• Maximizing water removal can significantly reduce the energy-

intensive drying process in paper-making.

• After pressing water from the paper pulp, re-wetting is occurring.

• Paper de-watering and re-wet phenomena are not currently well

understood primarily due to lack of sufficient data and reliable

models

Paper machine press section Close-up view of press nip

A B

Paper

Roll

Roll

Felt

Illustration of press nip

• The objectives of this project are to

– Leverage the HPC capabilities at LLNL and LBNL to

develop an integrated, multi-physics modeling framework

as a critical first step to understanding and reducing rewet

at the press section.

– Provide the pulp and paper manufacturing industry with

insights to inform the designs of more energy efficient

processes and equipment, resulting in energy reduction.

We leverage advanced simulation capabilities, experimental

measurements and paper machine data to develop an integrated,

multi-physics modeling framework.

• LLNL develops a continuum simulation framework to couple mechanical

and two-phase flow models

– Use Richards’ equation to describe two-phase flow in paper/felts

– Employ modified Cam-Clay model to describe paper plastic

deformation

• LBNL develops pore-scale flow modeling capabilities

– Perform high-resolution direct simulation of microscale flow

in complex pore structures in paper pulp and press felts

– Use pore-scale flow modeling to inform better parametrization of

porosity and permeability for continuum-scale computations

• Agenda 2020 provides the domain expertise and data to support model

calibration, validation, and application

Continuum modeling of coupled water

flow and deformation processes

• We have developed an integrated multi-physics modeling

framework for simulating two-phase (water and air) flow in

deformable porous pulp media during the wet pressing

process in paper making.

• We will work with paper industry to apply the developed

model to help guide press section configuration and roll/felt

design to minimize rewet.

integrated flow and

mechanical modeling

pore-scale flow model

paper machine

press data

paper/felt

CT and SEM data pore-scale deformation

laboratory

measurements

sheet

felt

continuum-scale flow

and mechanical model

paper

felt

UQ and sensitivity analysis

The model is able to fit the measured machine data, and predict

that pressing increases the web dryness from 20-35% to 30-50%.

1

shoe press nip configuration paper dryness evolution

felt

paper

312 mm

initial felt thickness = 3.5 mm

shoe press pressure

deformation and dryness of compressed paper/felt

paper thickness = 400 μm

water saturation distribution in compressed paper/felt

porosity distribution in compressed paper/felt

Model calibration spans scale, configuration and uncertainty

Non-linear pressure drop

Slice from felt CT image

3D pore-scale felt model using

geometry reconstructed from image

data (pressure shown) permeability k =

7.732x10-11 m2 Computed on 6912 cores

pore-scale flow in

uncompressed felt

K1/K2 = (ϕ1/ ϕ2)n

n ~ 5.0for continuum model

pore-scale flow in

compressed felt

computed bulk

porosity/permeability are

used to describe porosity-

permeability relationships.

two-phase flow simulation of diffusive and advective water movement in a synthetic felt

time = 0.12 time = 0.20

sensitivity analysis of paper dryness curves

made on one thousand realizationspaper dryness evolution at a roll press section

Joshua White, and Michael Homel (LLNL), and David Lange, David McDonald, and Stefan Probst–Schendzielorz (Agenda 2020)

This research was supported by the High-Performance Computing for Manufacturing Project Program (HPC4Mfg), managed by the U.S. Department of Energy Advanced Manufacturing Office within the Energy

Efficiency and Renewable Energy Office. It was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. LLNL-POST-725122