The Johanson Indices

The Johanson Indices are derived from measured consolidation pressures, time at rest and atmospheric conditions that simulate a plant's actual operating environment and test sample surfaces that simulate material handling equipment.

The Indices safely and accurately answer the most common material handling and equipment design questions including

  • How large should the hopper outlet be?
  • What hopper angle do I need?
  • What happens to material inside a bin if I use vibrators or air cannons? Where do I place them?
  • Do I need a hopper with flow at the walls? If so, what type?
  • Can I use a partial mass-flow hopper?
  • Do I need air injection to prevent limiting flow rate hangups?
  • What chute angles do I need?

The following table provides a brief description of the eight Johanson Indices.

Indices Definitions
Symbol         Name         Use Measurement Basis
AI Arching Index
(linear)
Sizes hopper outlets, feeder inlets, and predicts segregation potential. Proportional to the unconfined yield strength/bulk density ratio measures at initial solids pressures and the hopper outlet.
CI Chute Index
(degrees)
Determines chute angles at impact points and predicts buildup in conveying units. Derived from the chute surface adhesion after impact from a bulk solid.
HI Hopper Index
(linear)
Determines hopper and chute angles for flow and predicts chute segregation. Derived from the wall surface friction angle determine at either the hopper outlet or at the top of the hopper, whichever has the greater friction angle.
RI Rathole Index
(degrees)
Sizes outlets of funnel-flow bins to prevent ratholing and predicts lump formation in bags, trucks, containers and railroad cars. Proportional to the unconfined yield strength/bulk density ratio measured at initial solids pressures in funnel-flow bins.
BDI Bin Density Index
(weight/volume)
Determines bin capacity and loads. Equivalent to the bulk density measured at uniaxially applied pressures associated with the bin.
FDI Feeder Density Index
(weight/volume)
Determines feeder capacity and loads. Equivalent to the bulk density measure at uniaxially applied pressures associated the with hopper outlet.
FRI Flow Rate Index
(weight/time)
Determines maximum feed rates for deaerated powders, the need for air injection, segregation potential and flooding potential. Equivalent to the air flow resistance (permeability) measured at the hopper outlet; bulk density and density changes within the hopper.
SBI Springback Index
(percent)
Determines special hangup potential of materials that wind up elastically when compacted during storage. The elastic bulk modulus measured uniaxially.

Contact us at

Diamondback Technology, Inc.
7215 San Gabriel Road
Atascadero, CA 93422
(805) 544-3775
info@diamondbacktechnology.com


Johanson Indices

Developed in 1991 by Dr. Jerry R. Johanson, a renowned pioneer in bulk solids flow science, the eight Johanson Indices are an easy-to-understand method for characterizing bulk material flow properties that relate directly to solids flow problems and equipment design.


Forms & Documents


More Links


Free Paper