Powder Flow

A Survey of IFPRI work in Dry Particle Flow


Dry particle flows and/or gas-fluidized particles are ubiquitous in nature and industries that handle and/or produce bulk solids.  Industrial practitioners rely on routine handling of powders and granules for many applications.  In some cases, solids flow is inherent to a process, for example catalytic cracking of hydrocarbons in fluidized reactors.  In other cases, the solids are a constituent of a product, for example construction materials, agriculture, pharmaceuticals, foods, and a wide range of consumer products; solids flow is a necessary part of production processes, for example accurate feeding into a pressing operation, precise packaging, bin storage, reliable conveying and other handling operations.  On a systems scale, productivity and plant reliability are often constrained or limited by solids handling.  On a micro scale, critical quality attributes of a product may be rooted in particle characteristics.  Practitioners are regularly asked to develop and scale-up processes spanning these scales.  In addition to quality objectives, this task requires further attention to efficiency and sustainability.

In the context of industrial handling and processing, dry particulate flows may include:

  • granular materials that are relatively incompressible and non-cohesive;
  • granules that may and exhibit cohesive behavior, e.g., by adsorbed moisture or other liquid capable of forming liquid bridge adhesion between particles;
  • finely powdered materials that are both compressible and cohesive (e.g., due to van der Walls interactions) and may also include interactions due to adsorbed moisture.

Historical work by IFPRI

Dry particle flow has been a focus area of IFPRI since its inception.  Over this time, IFPRI has provided over 1 million USD in support of pre-competitive research in granular and powder flow, much of which forms the foundational basis of current practice in the field (IFPRI projects are listed in the Appendix).  

Several early IFPRI projects focused on handling of fine powder, especially fine powders subject to aeration.  Projects considered the control and rheology of aerated bulk powders, with implication to industrial problems including flooding, hopper discharge, and fluidization.  Interest in rheology extended to free-surface and fully fluidized flows.  

IFPRI supported extensive work on rapid shear flow as applicable to risers and circulating fluidized bed reactors, including both experimental and simulation-based studies.  These studies included seminal work in rapid shear flows, with focus on practical manipulation of gas-particle flows, i.e., implications of turbulence, bubbling, and coalescence leading to de-fluidization.  Several projects explored the use of electrical fields for manipulating and characterizing flow patterns in fluidized systems.

With IFPRI’s expansion in the late ‘90’s, including more food, consumer and pharmaceutical companies, projects extended to dry mixing operations and segregation challenges.  Results of these projects brought focus toward fundamental questions of the powder flow rheology, i.e., understanding flow and stress fields and their convective and dispersive characteristics.  

Concurrent with these application-driven projects, IFPRI supported a collaboration of physicists and engineers investigating relationships between single particle surface properties and bulk flow behavior, especially in context of humidity or other factors affecting surface interactions.  While showcasing advances in surface characterization, the results confirmed the difficulty of the multi-scale challenge.  

As a means to define problem statements pertinent to these challenges, IFPRI conducted a Powder Flow Workshop (2003).  The initial focus of the workshop on granular rheology was toward fundamental understanding and manipulation of flow and stress fields in industrial unit operations.  As an outcome, IFPRI supported a Working Group to summarize salient issues and grand challenge questions.  These combined efforts led to the experimental projects of Tardos (2010) and Behringer (2013), and culminated in an extended Collaboratory co-funded by the NSF, wherein modelers were invited to simulate the experimental systems.  Results and perspectives on the collaboratory process are published in “Dense granular flow — a collaborative study,” Powder Technology 284 (2015) 571–584.  Building from this, IFPRI has engaged in fundamental work linking powder flow with granular physics, and is now running an interactive Round-Robin exercise aimed at best practices in DEM modeling of dry flows.

IFPRI conducted another Powder Flow Workshop with leading academics and members companies in January 2017 to register current progress and identify future challenges. The workshop was organized in Amsterdam together with the European consortium T-MAPPP (Training in Multiscale Analysis of MultiPhase Particulate Processes and Systems). The workshop outlined successes and limitations of Discrete Element Modeling (DEM) numerical simulations, argued for a multiscale approach to practical problems, including particle characterization at the microscale, DEM, continuum modeling at the macroscale, and the establishment of boundary conditions relevant to the flow situation at hand.

Current focus areas

Dry powder rheology remains a grand challenge requiring integration and collaboration of theoretical, experimental and modeling programs.  Further, it is recognized that multiple regimes of particle flow co-exist in many industrial processes, complicating the challenge to apply fundamental theories and/or models.  With this in mind, there are two approaches in the current IFPRI program – 1) a unit operation focus, where projects address dry flow phenomena across multiple flow regimes (e.g., Die-filling; Chute segregation); and 2) a more detailed single-regime approach (e.g., Weakly-consolidated quasi-static flow; Particulate rheology at intermediate shear rates). 

Recent IFPRI grantees have included Karen Daniels (force chain visualization), Nathalie Vriend (free surface flow force chain characterization), Charlie Wu (powder die filling), Karen Hapgood (3D printing of model granular assemblies), Joseph McCarthy (granular segregation), Colin Hare (characterization of weakly consolidated powders), Indresan Govender (powder mixing rules), and Csaba Sinka (powder adhesion to surfaces).


  • Aerated Powder Flow; Nedderman, Rathbone (Cambridge) 1985.
  • Estimation of Powder Yield Locus & its Application to Design; Makino (Akita) 1985.
  • Method of Characterizing the Flow of Aerated Powders; Lloyd, Webb, (Loughborough), 1986.
  • Unification of Wet, Intermediate and Dry Granular Flow – A Theoretical Approach; Buggisch (Karlsruhe), 1988.
  • Characterization and Prediction of Powder Flow; Geldart, Woodcock (Bradford), 1989.
  • Granular Shear Flows: Fluid/Solid Solid Interfaces, Impact strengths and Self-Diffusion; Campbell, Zhang (USC), 1992
  • Rapid Shear of Fine Powders; Jackson (Princeton) 1992.
  • The Discharge of Fine Powders from Conical Hoppers;  Nedderman (Cambridge) 1993.
  • Turbulent Gas-Particle Flow in Vertical Risers; Jackson, Sundaresan, Dasgupta (Princeton) 1995.
  • Bubble and Elutriation Control in Fluidized Beds with Electric Fields; Colver et al. (Iowa) 1997.
  • A Review of Instrumentation for Dense Gas-Solid Flows; Louge (Cornell) 1997.
  • Mixing and Segregation in Industrial Processes; de Sliva (Telemark) 1997.
  • Measurement of Fluidization Dynamics in a Fluidized Bed using Capacitance Tomography; Beck, Dyakowski, Wang (UMIST) 1998
  • Discrete Particle Simulation of Gas-Solid Flow - Effect of Inter-Particle Collision; Tsuji, Tanaka et al. (Osaka) 1998.
  • Experimental Rapid Shear Flow; Louge (Cornell) 1998.
  • Rapid Shear Flow of Granular Materials; Sundaresan (Princeton) 1998.
  • Test Methods for Measuring Flow Properties of Bulk Solids, Schwedes (Braunschweig) 1999.
  • Suspension Paste and Powder Flow - Prospects of a Unified Approach; Melrose (Cambridge) 1999.
  • Characterisation of the Rheo-Mechanical Properties of Wet-Mass Powders; Tomas (Magdeburg) 2001.
  • Biaxial shear cell; Scarlett, Janssen (Delft) 2000.
  • Powder Mixing and Segregation; Muzzio et al (Rutgers) 2001.
  • Study on Fundamentals of Mixing of Powders with Emphasis on Cohesive Systems; Sommer (Munich) 2002.
  • Inter-particle Forces in Powder Flow; Pollock & Jones (Lancaster) and Geldart & Verlinden (Bradford) 2002.
  • Granular flows in the intermediate regime; Tardos (CUNY) 2002.
  • Studies of the fundamental interactions between a gas and agitated particles; Louge et al (Cornell) 2002.
  • From Wet to Dry; Brady (Caltech) 2003.
  • Workshop – Powder flow in the intermediate regime; Place et al (Bremen) 2003.
  • IFPRI Powder Flow Working Group.  Academic:  Behringer (Duke), Louge (Cornell), McElwaine (Cambridge), Pfeffer (NJIT), Sundaresan (Princeton), Schwedes (TU Braunschweig); Industrial:  Jacob (Dow), Halsey (Exxon), Michaels (Merck), Mort (P&G); IFPRI: de Jaeger, Place; NSF: Mountziaris.  2005.
  • Mixing of powders and granular materials by mechanical means; Bridgwater (Cambridge) 2008.
  • Constitutive characterization of dense flows in the intermediate regime; Tardos (CUNY), 2010.
  • Dynamics and Rheology of Cohesive and Deformable Granular materials; Behringer (Duke), 2013.
  • Dense Granular Flow, a Collaborative Study, NSF 1010008; Behringer (Duke), Campbell (USC),  Kondic (NJIT),  Shattuck (CUNY), Tardos (CUNY),  Wassgren (Purdue), 2012.
  • Die filling of aerated powders; Wu (Surrey), 2019.
  • Flowability of weakly-consolidated powders; Hare (Leeds/Surrey), current.
  • Prediction of powder segregation; McCarthy (Pittsburgh), current.
  • Non-local rheology of intermediate granular flows:  particle shape and size distributions; Daniels (North Carolina State), current.
  • Control of fluidity via boundary conditions, vibrations and stress fluctuations; Vriend (Cambridge), 2019.
  • Powder Mixing Rules; Govender (KwaZulu-Natal), current.
  • DEM Round-Robin, Developing Best Practice for the Simulation of Industrial Systems; Windows-Yule (Birmingham), current.