The main features of mass flow are listed below. It should be noted that the two main reasons for selecting mass flow are: - a). To avoid dead regions of storage for material that cakes or deteriorates with time in storage, and

b). To secure flow benefits.

The latter can normally be achieved by employing an 'Expanded Flow' pattern, where the lower section is mass flow up to a cross section that will not arch or rathole and the upper section wall angle is only required to self clear.

Advantages Drawbacks

No 'dead' regions of flowTall headroom,

reduced storage capacity

More predictable storage timesPotential wea on walls

Secures flow through smaller outlets The outlet must be

fully 'live'

Significantly reduces segregation Powder tests are

essential to

determine design

Resists 'Through-flow flushing'High wall pressure are

generated at the hip joint

The flow pattern is predictable The design relates only to

the condition of

the product tested

Flow is roughly ‘First-in, first-out’

Flow can be exploited to blend contents Any property change

may negate mass flow

Proven design guarantees reliable flow Flow rate is less than

non-mass flow

Notes - Mass flow not required to avoid dead regions of flow if

hopper fully empties every time before refill.

-It is essential that flow occurs over the total area of

the hopper outlet

-The flow velocity is not uniform across converging

sections of the hopper.

-Final portion of the discharge can concentrate

segregation

-‘Expanded Flow’, i.e. Mass flow at the outlet region

only, secures the outlet size benefits of Mass flow and

may suffice for bins that refill at a low level

-‘Mixed Flow’, i.e. where the non-mass flow channel

expands to meet the container walls below the stored

surface level, appears from above to be mass flow but

generates ‘kick’ stresses on the walls at indeterminate

and unpredictable wall locations

-Conical hoppers require walls approx. 10 degrees

steeper than Vee hoppers

-Additional benefits of lower wall angles and smaller

outlets may be gained by relaxation of the transverse

flow channel to a slot outlet, provided that the slot

develops fully live flow. ■

I am afraid that the chart structure on display is mess up from the way in which it was submitted. To avoid repeating the problem I have re-formatted the presentation of advantages/drawbacks.

Advantages

No 'dead' regions of flow

More predictable storage times

Secures flow through smaller outlets

Flow is roughly ‘First-in, first-out’

Significantly reduces segregation

Resists 'Through-flow flushing'

The flow pattern is predictable

Flow can be exploited to blend contents

Proven design guarantees reliable flow

Drawbacks

Tall headroom, reduced storage capacity

Potential wea on walls

Powder tests are essential to determine design

High wall pressure are generated at the hip joint

The design relates only to the condition of the product tested

Any property change may negate mass flow

Flow rate is less than non-mass flow

Notes - Mass flow not required to avoid dead regions of flow if hopper fully empties every time before refill.

- It is essential that flow occurs over the total area of the hopper outlet

- The flow velocity is not uniform across converging sections of the hopper.

- Final portion of the discharge can concentrate segregation

- ‘Expanded Flow’, i.e. Mass flow at the outlet region only, secures the outlet size benefits of Mass flow and may suffice for bins that refill at a low level

- ‘Mixed Flow’, i.e. where the non-mass flow channel expands to meet the container walls below the stored surface level, appears from above to be mass flow but generates ‘kick’ stresses on the walls at indeterminate and unpredictable wall locations

- Conical hoppers require walls approx. 10 degrees steeper than Vee hoppers

- Additional benefits of lower wall angles and smaller outlets may be gained by relaxation of the transverse flow channel to a slot outlet, provided that the slot develops fully live flow. ■