Kind sir,

you will find the angle of repose by using the method used by Tyler screening:

1. Find a 2 or 3 gallon bucket/pail. in your case thats 3 plus litres.

2 Fill it with cocoa beans to the top of the container.

3. After filling the bucket, lift the bucket past

your waist height and quickly dump it out in one swift action to the ground level, the angle of repose will be evident very quickly as long as no one touches the pile after it stops moving.

Using a protractor at ground level - or if you dump the cocoa beans on a table at your waist height should give you the angle quickly.

lzaharis ■

EL MOURABET FIKRI,

You can also find the repose angle of this in bulk material handling literature. The literature mentions that it is in the range of 30 to 44 degrees. The Indian Standard specification mentions it around 28 degree.

To me it seems it could be somewhere around 30 degree. Generally, surcharge angle for conveying is mentioned as 10 degrees.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Stricly speaking, an angle of repose for a given bulk material is dependent on the manner of formation. The most common interest is in a 'Poured angle of repose', which is usually formed by gently pouring a stream of the product onto a growing pile. Whilst this can be done at a small scale, it should be remembered that high feed rates and extended drop heights will influence the results. There is also a small difference between the stable residual angle near the tip of a pile and the inclination of the surface at a larger diameter. This is because the rate of divergence decreases as the diameter grows and the ultimate angle approaches a flat surface repose angle, i.e. one that would be formed with no convergence or divergence of the formative flow regime. This particular condition can be measured by allowing a pile to form near the edge of a table or other straight edge over which the bottom of the pile can fall away. This boundary angle is the most independent of the formation means.

An anlternative, and steeper inclination, is usually given by a 'Drained angle of repose' measurement. In these circumstances the material flows in a converging cone to an outlet hole and the steepness of the slope tends to increase with nearness to the outlet because of transverse particle interference as the flowing product focusses more tightly.

Obviously, these measurements are dependent on the condition of the product and consistent results can only be obtained with non-cohesive materials. Beans and similar free flowing products will normally yield consistent values, unless the are wet or subject to change in conditionwith age, pressure or damage.

Ultimately, the issue is establishing the purpose of the measurement. This particular value has to be carefully defined and consistantly obtained to be of value, the most common use being allowance for ullage in storage or spillage from containers or dynamic flow streams. In this latter case the stability of the bulk has to be taken into account. ■