Introduction

     In the processing, handling and storage of agricultural produce, “granular materials” means Grain, fruit and seeds and these granular materials possesses frictional properties (Mohsennin 1978). According to (Ogbonnaya and Fatai, 2007) the rapid method of assessing the behavior of granular mass is by the determination of “angle of repose”.      If a solid is poured on to plane surface, it will form an approximately conical heap and the angle between the sloping side of the cone and the horizontal is the angle of repose. When determined in this manner, it is referred to as dynamic angle of repose or the poured angle. In practice, the heap will not be exactly conical and there will be irregularities in the sloping surface. Furthermore, there will be tendency for some materials to roll down from the top and collect at the base, thus giving a greater angle at the top and a smaller angle at the bottom.      The angle of repose was defined by Mohsennin in 1978 as the angle with horizontal at which the materials will stand when piled. Furthermore the angle of repose of these granular materials is affected by many of it physical properties such as moisture content, shape indices etc.

Why do we need to determine the angle of repose of agricultural materials

     Agricultural materials after harvesting need some handling technique, others need storage and other need processing all these can’t be done easily without the use of machine. In designing a machine that will handle, store and process agricultural materials we need the properties of this materials be it physical, chemical and even biological. One of the physical properties that need to be determined is the angle of repose. Angle of repose is necessary in the design of hoppers used for processing, also in the design of dryers.

Objective(s) of the Experiment

     The objective of this experiment is to determine the angle of repose of some selected agricultural produce.

Equipments and Materials Needed

1. Equipment and Materials Needed for Improvised Crude Method:

1. Selected agricultural produce
2. An open ended can
3. A ruler

2. Materials Needed for Standard Experimental Procedure in Determination of Angle of Repose of Agricultural Materials:

1. Selected agricultural produce to be determined
2. Fowler and Wyatt apparatus

Procedures

1. Procedures for Improvised Crude Method

1. Fill the empty open ended can with the selected agricultural produce
2. Slightly remove the can
3. Take the diameter and height of the heap formed.
4. Calculate the radius by dividing the diameter by 2

2. Procedures for Standard Experimental Procedure in Determination of Angle of Repose of Agricultural Materials

1. The apparatus is filled with granular solids whose angle of repose is to be determined.
2. The solid is allowed to escape from the box leaving a free standing cone of solid on the circular platform.
3. With the aid of the meter rule in the box, the indicated heights were measured and the angle of repose θr can be obtained from the geometry of cone from Eq. 2 below:

Results and Calculations

1. Improvised Crude Method
The angle of repose is calculated with the mathematical formulae (equation 1) below:

2. Standard Experimental Procedure in Determination of Angle of Repose of Agricultural Materials
The angle of repose is calculated with the mathematical formulae (equation 2) below:

Where: Hc = height of cone from datum; Hp = height of platform; Hc – Hp = height of cone of solids; Dp = diameter of circular platform.

Discussion and Conclusion

     The angle of repose determined can be used in design of bins, hoppers and storage structures.

References

1. Mohsenin, N.N. (1978). "Physical Properties of Plant and Animal Materials: Structure, Physical Characteristics and Mechanical Properties". 1st ed. 1970, republished 1978. Gordon and Breach Science Publishers, New York, NY, USA.
2. Ogbonnaya, C. and Fatai, B.A. (2017). "Development of an apparatus for measuring Angle of Repose of Granular Materials". Department of Agricultural Engineering, OAU. OAU, ife Nigeria.

Credits: Wasiu Mayowa Tiamiyu. Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria.