Greg Mehos, Ph.D., P.E.

Powder Flow

Hopper Design

Process Vessels




  • If you have a Freeman Technology FT4, Schulze RST, Brookfield Engineering PFT, or an E&G Associates iShear (Peschl) tester you should be able to PREDICT flow behavior rather than RANK flowability; often when you use your tester to rank your materials, powders that were deemed to have good flowability often have flow problems when handled. I will show you how to use the test results to predict if a powder will flow reliably in existing equipment, modify the equipment, or design new equipment.
  • The 9th edition of Perry's Handbook was published this year, and I am excited to be the author of the subsection on powder flow and hopper design.  
  • I have a doctorate in chemical engineering from the University of Colorado, but I like to say that I received a Ph.D. in process development from Cabot Corporation and a Ph.D. in bulk solids handling from Jenike & Johanson, Inc.
  • My approach to consulting is to teach clients the fundamentals of bulk solids storage and handling so that they can measure powder flow properties, design bulk solids handling equipment, and solve powder handling problems by themselves.



  • Process development
  • Functional design recommendations
  • Solutions to powder flow problems

Process Vessels

Moving powder bed dryers and purge vessels

Moving bed heat exchangers

Moving bed reactors


  • Workshops
  • Seminars
  • Tester training


Quotations and Proposals

Please reach out at your convenience so we  can discuss your project.  

Greg Mehos, Ph.D., P.E.

4 Crusade Road, Westford, Massachusetts 01886, United States


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When fine powders are handled, the desired discharge solids discharge sometimes cannot be reached due to vacuum that naturally develops near the hopper outlet. This results in counter flow of air into the hopper outlet, which can hinder flow. By properly adding a small amount air into the hopper, the adverse gas pressure gradient is removed, and the solids discharge rate is dramatically increased.

If you have a shear  cell tester, instead of finding a powder's FFC value, you should use the test results to determine the size of a hopper outlet required to prevent obstructions to flow and the recommended mass flow hopper angle.  This video provides a step-by-step procedure for using Jenike's method to design a mass flow hopper. 

Favorite Places (I am not a rep, but these places are good!)

Gamlen Instruments

Powder Compaction Analysis

Rocky DEM

Discrete Element Method Software

Young Industries

Materials Handling Equipment

Solids Handling Technologies


International Fine Powder Research Institute

Institute for Briquetting and Agglomeration

Size Enlargement Specialists


Schulze Ring Shear Testers


Contract R&D and Toll Manufacturing

FEECO International

Wet Agglomeration Equipment


  • My Hopper Design Cliff Notes provide a nice summary of flow property test methods and bin design.  When I give workshops, I provide these notes along with a spreadsheet that performs the calculations.
  • Caking and its Prevention is the non-copyright version of an article that I wrote for Chemical Engineering magazine.
  • Optimization of Pharmaceutical Formulations for Flow shows how Jenike's flowability coefficient FFC can be misinterpreted.  It's better to measure  the flow properties of a powder over a range of consolidation pressures so that critical hopper outlet dimensions and hopper angles can be calculated.
  • I periodically add other documents on powder handling and processing.  Be sure to visit and check for updates.

Hopper Design Cliff Notes (pdf)


Caking and Its Prevention (pdf)


Optimization of Pharmaceutical Formulations for Flow (pdf)


Moving Bed Process Vessels (pdf)


Wet Granulation of Fumed Silica (pdf)


Choosing Agglomeration Processes (pdf)


CV (pdf)


URI Notes (Password Required) (docx)


Perry's Handbook Bulk Solids Testing and Hopper and Chute Design (pdf)


St. Baldrick's Foundation

A good friend of mine is fighting cancer, and her daughter is shaving her head to raise money for cancer research.  Please consider donating.

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