It is an unfortunate fact that many hopper and silo installations are plagued by discharge problems.
Ajax Equipment has developed an interactive hopper design tool to assist engineers. A design flow chart is used to examine flow problems and present options for improvements as well as a very useful capacity calculation for hopper shapes with wall slope and outlet size data to achieve mass flow for conical, pyramid, transition and chisel-shaped hoppers.
For more information on achieving good hopper designhoppercalcs.htm based on an understanding of the flow behaviour of Bulk Solids click here.hoppercalcs.htm
Bin - Orifice Size & Shape, Wall Friction and Slope,
Flow - Rate, Frequency of Starts
Although no size of opening is ‘safe’, the probability of a stoppage falls off rapidly as outlet increases above four times the largest particle dimension.
A minor change in wall angle next to the outlet can reduce the probability of blockage by generating wall slip with an ‘Expanded Flow’ form of Hopper construction.
May be aggravated by the air demand of void expansion and lead to ‘Slurping’, a cyclic increase of flow rate as powder ‘rains’ from an increasing size of arch, followed by a sudden collapse of the arch as its span exceeds the ‘critical orifice size’
Interactive Hopper Design Tool
Interactive Hopper Design Tool
It is an unfortunate fact that many hopper and silo installations are plagued by discharge problems.
Ajax Equipment has developed an interactive hopper design tool to assist engineers. A design flow chart is used to examine flow problems and present options for improvements as well as a very useful capacity calculation for hopper shapes with wall slope and outlet size data to achieve mass flow for conical, pyramid, transition and chisel-shaped hoppers.
For more information on achieving good hopper designhoppercalcs.htm based on an understanding of the flow behaviour of Bulk Solids click here.hoppercalcs.htm
Structural Arching
Is a Stochastic Phenomenon depending on:
Particle - Size & Size distribution, Shape, Contact Friction
Bin - Orifice Size & Shape, Wall Friction and Slope,
Flow - Rate, Frequency of Starts
Although no size of opening is ‘safe’, the probability of a stoppage falls off rapidly as outlet increases above four times the largest particle dimension.
A minor change in wall angle next to the outlet can reduce the probability of blockage by generating wall slip with an ‘Expanded Flow’ form of Hopper construction.
http://www.ajax.co.uk/model2.htmmodel2.htm
Cohesive Arching
May be aggravated by the air demand of void expansion and lead to ‘Slurping’, a cyclic increase of flow rate as powder ‘rains’ from an increasing size of arch, followed by a sudden collapse of the arch as its span exceeds the ‘critical orifice size’
http://www.ajax.co.uk/model3.htmmodel3.htm
Segregation
Caused by ‘Repose Slope formation’ can be reduced by means of a ‘Multiple-point Fill’ technique.
A degree of Homogeneity can be restored on discharge by means of ‘Tributary collection’
That is, using flow inserts to blend material that is extracted from different regions of the stored mass.
More information on AJAX Equipment1083 ajax equipment.htm
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