There was a very comprehensive article in Bulk Solids journal back in the early 90's. I haven't seen anything of comparable quality and detail since.

You can maybe do a search hereabouts and find where it lies. (There are also more recent articles within the forums: so if Lyle Brown reads this you might benefit from his very impressive recall.)

I remember it used a Perspex shell and was filled with different colours of sand to trace the movement within the bin.

The side panels were not adjustable but the vertical cross sections could be observed through insertable bulkheads. There is probably more sophisticated instrumentation available these days.

Similitude of moisture effects in a silo would be a ground breaker. Moisture plays havoc with ensiled sugar and the situation is complicated by advancing solar heating on the external walls throughout the course of 24 hours. There will be many materials suffering this effect.

Wall stress studies have been well hammered (rubber type) on many occasions in eg Australian Standards. For insert workings you really need to Ask Lyn.

I imagine the main thing DEM has going for it is the ease of reproduction of the particle properties. Probably you can reconstruct the element database whereas I can't imagine how to separate different coloured sands: even with today's instruments.

Good luck in your endeavour. ■

Originally Posted by Achint

We are constructing a pilot scale silo for research purposes. The silo is of wedge-shaped geometry with variable angle and variable outlet size. We have some ideas about experiments to conduct with this setup, but are looking for more. If anyone can provide suggestions about materials with which testing needs to be done, or other possibilities (e.g., measuring wall stress distribution, addition of asymmetric insert, etc., ), it would be much appreciated!

Originally Posted by johngateley

There was a very comprehensive article in Bulk Solids journal back in the early 90's. I haven't seen anything of comparable quality and detail since.

You can maybe do a search hereabouts and find where it lies. (There are also more recent articles within the forums: so if Lyle Brown reads this you might benefit from his very impressive recall.)

I remember it used a Perspex shell and was filled with different colours of sand to trace the movement within the bin.

The side panels were not adjustable but the vertical cross sections could be observed through insertable bulkheads. There is probably more sophisticated instrumentation available these days.

Similitude of moisture effects in a silo would be a ground breaker. Moisture plays havoc with ensiled sugar and the situation is complicated by advancing solar heating on the external walls throughout the course of 24 hours. There will be many materials suffering this effect.

Wall stress studies have been well hammered (rubber type) on many occasions in eg Australian Standards. For insert workings you really need to Ask Lyn.

I imagine the main thing DEM has going for it is the ease of reproduction of the particle properties. Probably you can reconstruct the element database whereas I can't imagine how to separate different coloured sands: even with today's instruments.

Good luck in your endeavour.

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As john has said its a wide plateau to examine so to speak.

Every hopper bin or silo is different because of the required

throughput for production quotas and actual needs in the case

of a power plant for example

The issue of the angle of repose of any of the material at rest is but one issue.

Size and weight of the material stored also affect the hypothesis and affects experiment and conclusion.

The other nasty one is mass sliding that can and will blow a silo or bin apart like an explosion-been there done that

The other huge issue is inconsistant material size- mine ore that is sedimentary in nature like halite that is mined in narrow seams with shale cap rock is a very nasty ore to deal with because it will bridge and rathole.

Ratholes in Bins are not your friends and they have and do kill many people.

Grain storage is another issue that also has many of the same problems with mass slides

and bridging and death by asphyixiation to the persons in the bin that do not have the proper safety equipment

which are full body harnesses/tag lines/ tag line person to pay ou the line and pull it back in and a spotter to

watch the bin contents and the person in the bin.

The other muddy cricket pitch is the Hopper or bin bottom/drawdown point and the method of drawdown.

Gravity is not your friend unless you have altitude/vertical bins with wide chute long chutes that are mounted at a pivot point at the bottom of the bin thaat permit large tonnages of material to simply drop out and raise and lower using wire rope and a counterbalance weight

to lower and raise them with a winch. The iron ore docks on Lake Superior are an excellent example of this.

My rule is simply leave very little opportunity for anything and I mean anything to bridge or rat hole by providing

the proper sized drawdown point to eliminate any and all potential for a restriction/bridging/rat hole to occur.

If the hopper is a circular bin with a conical base you have to have adraw down hole as large as the method of draw down.

The spillage is controlled by skirt boards and a draw down regulating gate at the apron feeder in my example.

Some folks use short conveyor belts for drawdown, some drawdown points are controlled and operated by vibrating pan

feeders, some drawpoints use apron feeders.

I am reminded everyday with the fact that my employers saving money and my uncle's actions as the supervisor

killed my closest friend and a co-worker becuase the mine engineers simply did not pay attention to simplicity

wherein run of mine sized mined materials stored in bins are only adequately moved with brute force using an

apron feeder and this they failed to heed as it was already being done in the old screen plant with the apron

feeder under the 75 ton recieving bin.

There is no one size fits all approach simply because there cannot be.

The higher the drawdown angle of the greater ability the material has

to fall and be drawn away as the material cannot "stick", bridge or rat hole. ■

Dear Achint,

It seems that you are searching for a subject to do research on, rather than having a specific subject to investigate.

Starting a Hopper Discharge Research with cement is quite complicated, as cement is existing in (very) fluidizable and consolidated conditions, influencing the flow properties in a hopper significantly.

The influence of humidity (water vapor) on cement is well known. (concrete)

If a cement silo or hopper is filled pneumatically, the humidity and/or condensation problem has happened before the cement is stored in the hopper.

Cement storage and silo flow is in practice a solved issue as there are a huge number of silos around the world, which all work satisfactorily, due to the application of fluidizing floors and air injection nozzles.

This is an important and worthwhile subject to investigate.

Success ■

Be aware that, although you have a pilot scale test rig, you cannot simply scale your test materials down in any but the simplest case of non-cohesive, free-flowing material. If you attempt to use a scaled down version of a cohesive material, then the process of scaling down is likely to increase the cohesive properties. As mentioned elsewhere, moisture content does not scale with size either.

If you are going to examine bridging effects, then you will need to scale your material in a linear fashion with the relative scale of the hopper. ■

Originally Posted by Achint

We are constructing a pilot scale silo for research purposes. The silo is of wedge-shaped geometry with variable angle and variable outlet size. We have some ideas about experiments to conduct with this setup, but are looking for more. If anyone can provide suggestions about materials with which testing needs to be done, or other possibilities (e.g., measuring wall stress distribution, addition of asymmetric insert, etc., ), it would be much appreciated!

Jiri Smid

Dear Achint,

I can help you with two-directional stress gages for measurements of normal and shear stresses on the wall. Stress gages could be manufactured in my home country, the Czech Republic. ■