Papers by Lemi Demissie
Journal of Applied Fluid Mechanics , 2024
Cyclone separators are commonly used in pneumatic conveyor systems due to their low cost and abil... more Cyclone separators are commonly used in pneumatic conveyor systems due to their low cost and ability to separate solid particles from gas streams. Understanding pressure drop in cyclone separators is crucial for designing, developing, and optimizing efficient cyclone separators for pneumatic conveyors. The swirling motion within the cyclone during particle-gas separation can cause a pressure drop in the pneumatic conveyor. This study investigates the pressure drop across cyclone separators in pneumatic conveyor systems for Teff grain, both experimentally and computational fluid dynamics (CFD) with discrete particle modeling (DPM) simulation. The study utilized the Lapple cyclone separator model and examined the effects of varying cyclone size (0.75D, 0.9D, and 1D for D=200mm), inlet air velocity (10m/s, 14m/s, 18m/s, 22m/s), and material mass flow rate (0.009kg/s, 0.03kg/s, 0.044kg/s, 0.067kg/s) on the pressure drop across the cyclone separator. The results show that there is strong agreement between experimental and CFD-DPM simulation results. The simulation results accurately represent experimental results, with R-squared value of 0.99 and a residual sum of squares of 38.018. Furthermore, the best curve fit was obtained between the power losses due to pressure drop across the cyclone separator and air mass flow rate. These findings demonstrate that the pressure drop and associated power losses across cyclone separators in pneumatic Teff grain conveyors can be effectively determined using both experimental and simulation methods. This finding can inform the design and optimization of efficient cyclone separators for pneumatic Teff grain conveyor systems.
Soil is a granular medium that varies in composition from organic peat to gravel and that may
con... more Soil is a granular medium that varies in composition from organic peat to gravel and that may
contain various amounts of water. The soil physical system is continually being subjected to
external forces and is, therefore, dynamic. These external forces may be environmental climate,
plants, animals, and micro-organisms or mechanical forces applied by man using some type of
machine. Tillage is the manipulation of soil by mechanical forces. The purpose of tillage tool
design is to create a mechanical system, that is, a tillage machine or a series of machines capable
of controlling the applied forces in order to achieve a desired soil condition. In tillage tool
design, a limited number of abstract factors become of primary importance. In order to utilize the
capability of soil for some specific purpose, the soil must be manipulated (changed, moved, or
formed) to a desired condition. The manipulation is accomplished with a tillage tool by moving
the tool through the soil. To obtain different final soil conditions, only the shape of the tool and
the manner of moving the tool can be varied. The tool is varied in some manner and acceptable
designs are identified when the resulting soil condition is adjudged to be satisfactory.
Quantitative descriptions or representations of the final soil condition are seldom used and, in
addition, the forces required to move the tool are frequently not quantitatively assessed.
Generally, no effort is made to describe the reaction of the soil. Consequently, design today
merely accepts what occurs; it does not control what occurs. Thus, even though the need for
design is great, design in the true sense of the word is not accomplished and probably will not be
accomplished until quantitative information is available.
Teaching Documents by Lemi Demissie
Lemi Demissie Boset, 2023
The previous studies were confined to direct stresses caused on planes at right to the line of ac... more The previous studies were confined to direct stresses caused on planes at right to the line of action of applied loads and to s our studies to the stresses caused on planes loads. However complex the system of forces acting on a body be, yet it locate three mutually perpendicular planes which carry purely normal stresses. Planes within a material such that the resultant stresses across them are wholly normal stresses or planes across which no shearing stresses occur are termed as p planes and the stresses acting on these planes are called principal stresses. The stress intensity on one of these planes at a point is more than on the other two planes and on the other one it is least of all. Below we proceed to investigate a fe 1.1. Consider the general case, shown in Fig. 1.1, of a bar under direct load F giving rise to stress σ Let the block be of unit depth; then considering the equilibrium of forces on the resolve forces perpendicular to BC, Now resolving forces parallel to BC, The stresses on the inclined plane, therefore, are not simply the resolutions of σ perpendicular and tangential to that plane. The direct stress σ σ y Strength of Material II, Teaching Material 1.0. The previous studies were confined to direct stresses caused on planes at right to the line of action of applied loads and to s our studies to the stresses caused on planes loads. However complex the system of forces acting on a body be, yet it locate three mutually perpendicular planes which carry purely normal stresses. Planes within a material such that the resultant stresses across them are wholly normal stresses or planes across which no shearing stresses occur are termed as p planes and the stresses acting on these planes are called principal stresses. The stress intensity on one of these planes at a point is more than on the other two planes and on the other one it is least of all. Below we proceed to investigate a fe 1.1. Consider the general case, shown in Fig. 1.1, of a bar under direct load F giving rise to stress σ Let the block be of unit depth; then considering the equilibrium of forces on the resolve forces perpendicular to BC, Now resolving forces parallel to BC, The stresses on the inclined plane, therefore, are not simply the resolutions of σ perpendicular and tangential to that plane. The direct stress σ y when θ = 90 Strength of Material II, Teaching Material 1.1. Stresses on oblique planes Consider the general case, shown in Fig. 1.1, of a bar under direct load F giving rise to stress σ Let the block be of unit depth; then considering the equilibrium of forces on the resolve forces perpendicular to BC, Now resolving forces parallel to BC, The stresses on the inclined plane, therefore, are not simply the resolutions of σ perpendicular and tangential to that plane. The direct stress σ when θ = 90 Strength of Material II, Teaching Material Stresses on oblique planes Consider the general case, shown in Fig. 1.1, of a bar under direct load F giving rise to stress σ Let the block be of unit depth; then considering the equilibrium of forces on the resolve forces perpendicular to BC, Now resolving forces parallel to BC, The stresses on the inclined plane, therefore, are not simply the resolutions of σ perpendicular and tangential to that plane. The direct stress σ when θ = 90 Strength of Material II, Teaching Material Stresses on oblique planes Consider the general case, shown in Fig. 1.1, of a bar under direct load F giving rise to stress σ Let the block be of unit depth; then considering the equilibrium of forces on the resolve forces perpendicular to BC, But AB = BC sin θ Now resolving forces parallel to BC, Again AB = BC sin θ, The stresses on the inclined plane, therefore, are not simply the resolutions of σ perpendicular and tangential to that plane. The direct stress σ when θ = 90
Uploads
Papers by Lemi Demissie
contain various amounts of water. The soil physical system is continually being subjected to
external forces and is, therefore, dynamic. These external forces may be environmental climate,
plants, animals, and micro-organisms or mechanical forces applied by man using some type of
machine. Tillage is the manipulation of soil by mechanical forces. The purpose of tillage tool
design is to create a mechanical system, that is, a tillage machine or a series of machines capable
of controlling the applied forces in order to achieve a desired soil condition. In tillage tool
design, a limited number of abstract factors become of primary importance. In order to utilize the
capability of soil for some specific purpose, the soil must be manipulated (changed, moved, or
formed) to a desired condition. The manipulation is accomplished with a tillage tool by moving
the tool through the soil. To obtain different final soil conditions, only the shape of the tool and
the manner of moving the tool can be varied. The tool is varied in some manner and acceptable
designs are identified when the resulting soil condition is adjudged to be satisfactory.
Quantitative descriptions or representations of the final soil condition are seldom used and, in
addition, the forces required to move the tool are frequently not quantitatively assessed.
Generally, no effort is made to describe the reaction of the soil. Consequently, design today
merely accepts what occurs; it does not control what occurs. Thus, even though the need for
design is great, design in the true sense of the word is not accomplished and probably will not be
accomplished until quantitative information is available.
Teaching Documents by Lemi Demissie
contain various amounts of water. The soil physical system is continually being subjected to
external forces and is, therefore, dynamic. These external forces may be environmental climate,
plants, animals, and micro-organisms or mechanical forces applied by man using some type of
machine. Tillage is the manipulation of soil by mechanical forces. The purpose of tillage tool
design is to create a mechanical system, that is, a tillage machine or a series of machines capable
of controlling the applied forces in order to achieve a desired soil condition. In tillage tool
design, a limited number of abstract factors become of primary importance. In order to utilize the
capability of soil for some specific purpose, the soil must be manipulated (changed, moved, or
formed) to a desired condition. The manipulation is accomplished with a tillage tool by moving
the tool through the soil. To obtain different final soil conditions, only the shape of the tool and
the manner of moving the tool can be varied. The tool is varied in some manner and acceptable
designs are identified when the resulting soil condition is adjudged to be satisfactory.
Quantitative descriptions or representations of the final soil condition are seldom used and, in
addition, the forces required to move the tool are frequently not quantitatively assessed.
Generally, no effort is made to describe the reaction of the soil. Consequently, design today
merely accepts what occurs; it does not control what occurs. Thus, even though the need for
design is great, design in the true sense of the word is not accomplished and probably will not be
accomplished until quantitative information is available.