Important Engineering properties such as physical, thermal and aero & hydrodynamic properties of cereals, pulses and oilseed

1. IMPORTANT ENGINEERING PROPERTIES
SUCH AS PHYSICAL, THERMAL AND AERO &
HYDRODYNAMIC PROPERTIES OF CEREALS,
PULSES AND OILSEED
Dr. Ajay Singh Lodhi
Assistant Professor
College of Agriculture, Balaghat
Jawahar Lal Krishi Vishwa Vidyalaya, Jabalpur (M.P.)

2. Physical Properties
Shape and size
 Shape of the grain is connected with the geometrical form of the grain.
 Size of the grain refers to the characteristics of an object which in term
determine how much space it occupies and, within limits, can be
described in terms of length, width, and thickness.
 The Shape and size together with other characteristics of the grains is
important in the design of the seed grader. These factors determine the
free flowing or bridging tendencies of the seed mass, and therefore,
determine the suitable handling and feeding equipment.
 Sphericity and equivalent diameters are also used to describe the
shape and size, respectively for the grains.

3.  Sphericity:- The sphericity (φ) defined as the ratio of the
surface area of sphere having the same volume as that of
the grain to the surface area of the grain.
 Sphericity can be calculated from the axial dimensions of
the grain as follows:
Where
𝑑𝑖 = is the diameter of largest inscribed circle
𝑑𝑐 = is the diameter of smallest circumscribed circle
of the particle
 The sphericity of different grains varies widely.
𝑆𝑝ℎ𝑒𝑟𝑖𝑐𝑖𝑡𝑦 =
𝑑𝑖
𝑑𝑐

4. Roundness :
 It is a measure of the sharpness of the solid material. The
most widely accepted methods for determining the
roundness of irregular particle are given below:
𝑅𝑜𝑢𝑛𝑑𝑛𝑒𝑠𝑠 =
𝐿𝑎𝑟𝑔𝑒𝑠𝑡 𝑝𝑟𝑜𝑗𝑒𝑐𝑡𝑒𝑑 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑡ℎ𝑒 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒 𝑤ℎ𝑒𝑛 𝑖𝑡 𝑖𝑠 𝑖𝑛 𝑛𝑎𝑡𝑢𝑟𝑎𝑙 𝑟𝑒𝑠𝑡 𝑝𝑜𝑠𝑖𝑡𝑖𝑜𝑛, 𝐴𝑝
𝐴𝑟𝑒𝑎 𝑜𝑓 𝑠𝑚𝑎𝑙𝑙𝑒𝑠𝑡 𝑐𝑖𝑟𝑐𝑢𝑚𝑠𝑐𝑟𝑖𝑏𝑖𝑛𝑔 𝑐𝑖𝑟𝑐𝑙𝑒, 𝐴𝑐
𝑅𝑜𝑢𝑛𝑑𝑛𝑒𝑠𝑠 𝑟𝑎𝑡𝑖𝑜 =
𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑐𝑢𝑟𝑣𝑎𝑡𝑢𝑟𝑒, 𝑟, 𝑜𝑓 𝑡ℎ𝑒 𝑠ℎ𝑎𝑟𝑝𝑒𝑠𝑡 𝑐𝑜𝑟𝑛𝑒𝑟
𝑀𝑒𝑎𝑛 𝑟𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒, 𝑅

5. Bulk Density
 The bulk density of a grain can be determined by weighing
a known volume of grain filled uniformly in a measuring
cylinder.
 The following equation is used to calculate the bulk density
of the material:
𝜌𝛽 =
𝑊
𝑉
Where
 𝜌𝛽 is the bulk density, g/cc or kg/m3
 𝑊 is the weight of the material, g or kg
 𝑉 is the volume of the material, cc or m3

6. True Density
 The mass per unit volume of a material excluding the void
space is termed as its true density.
 The simplest technique of measuring true density is by
liquid displacement method, where tube is commonly
used. The expressions used for calculation of true volume
are given as follows:
𝑉𝑜𝑙𝑢𝑚𝑒 𝑐𝑐 =
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑑 𝑊𝑎𝑡𝑒𝑟, 𝑔
𝑊𝑒𝑖𝑔ℎ𝑡 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟, 𝑔/𝑐𝑐
𝑉𝑜𝑙𝑢𝑚𝑒 𝑐𝑐 =
(𝑊𝑒𝑖𝑔ℎ𝑡 𝑖𝑛 𝑎𝑖𝑟 − 𝑊𝑒𝑖𝑔ℎ𝑡 𝑖𝑛 𝑊𝑎𝑡𝑒𝑟), 𝑔
𝑊𝑒𝑖𝑔ℎ𝑡 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟, 𝑔/𝑐𝑐

7. Porosity
 It is defined as the percentage of volume of inter-grain
space to the total volume of grain bulk. The percent void of
different grains in bulk is often needed in drying, airflow,
and heat flow studies of grains.
 Porosity depends on (a) shape, (b) dimensions, and (c)
roughness of the grain surface.
 Porosity of some crops is tabulated as follows:
 The grain porosity can be measured by using an air
comparison pycnometer or by the mercury displacement
method (Thompson and Issas, 1967).
Grain Porosity (%)
Corn 40 – 45%
Wheat 50 – 55%
Paddy 48 – 50%
Oats 65 – 70%

8. Coefficient of Friction and angle of repose
 Angle of repose and frictional properties of grains play an
important role in selection of design features of hoppers,
chutes, dryers, storage bins, and other equipment for grain
flow.
Coefficient of Friction
 The coefficient of friction between granular materials is
equal to the tangent of the angle of internal friction for the
material. The frictional coefficient depends on (a) grain
shape, (b) surface characteristics, and (c) moisture content.

9. Angle of Repose
 The angle of repose of grain can be determined by the
following method.
 Grain is poured slowly and uniformly onto a circular
platform of 6.5 cm diameter to form a cone. The height of
this cone is measured using a traveling microscope.
 The angle of repose of grain at different moisture contents
is determined from the geometry of the cone formed (Dutta
et al., 1988).
 It is the angle made by the surface of the cone with
horizontal.
 “The angle of repose is the angle between the base and
the slope of the cone formed on a free vertical fall of the
granular material to a horizontal plane. The size, shape,
moisture content and orientation of the grains affect the
angle of repose.”

10.  Angle of Repose is calculated using the following equation:
𝜑𝐴𝑅 = 𝑡𝑎𝑛−1
2(𝐻𝑎 − 𝐻𝑏)
𝐷𝑏
Where
𝜑𝐴𝑅 is the angle of repose, degrees
𝐻𝑎 is the height of the cone, cm or m
𝐻𝑏 is the height of the Platform, cm or m
𝐷𝑏 is the diameter of the
platform, cm or m

11. THERMAL PROPERTIES
 Specific heat : The specific heat may be defined as the amount
of heat in kilo-calories that must be added to or removed from 1
kg of a substance to change its temperature by 1°C.
 The specific heat of wet agricultural material is the sum of
specific heats of bone dry material and its moisture content.
 If Cd and Cw are the specific heats of bone dry material and
water respectively, and in is the moisture content of the material
in percent wet basis, then the specific heat can be expressed as
given below
𝐶 =
𝑚
100
𝐶𝑤 +
100−𝑚
100
𝐶𝑑
𝑘𝑐𝑎𝑙
𝐾𝑔
℃
m is the moisture content of the grain, percent (wet bulb
temperature)
The specific heat of bone dry grain varies from 0.35 to 0.45 kcal/kg or
1.46 to 1.88 kJ/kg °C.

12. Thermal conductivity :
 The thermal conductivity is defined as the amount of heat flow
through unit thickness of material over a unit area per unit time
for unit temperature difference.
 The thermal conductivity of the single grain varies from 0.3 to
0.6 kcal/(m·h °C), whereas the thermal conductivity of grains in
bulk is about 0.10 to 0.15 kcal/(m·h °C), which is due to the
presence of air space in it. The thermal conductivity of air is
0.02 kcal/(m·h °C) only.
 The thermal conductivity can be expressed by the following
equation
𝑄 = 𝐾𝐴∆𝑇
Where Q = amount of heat flow, k cal
A= area, m2
∆𝑇 = temperature difference in the direction of heat
flow, °C
K= thermal conductivity, k cal/m.hr.°C

13. AERO AND HYDRODYNAMIC PROPERTIES
Terminal Velocity:
 The air velocity at which an object remains suspended in a
vertical pipe under the action of the air current is called terminal
velocity of the object.
 Thus, in free fall, the object attains a constant terminal velocity,
Vt, when the gravitational accelerating force, Fg, becomes equal
to the resisting upward drag force Fr. Hence, Fg = Fr when V =
Vt.
𝑉𝑡 =
2𝑊(𝜌𝑣 − 𝜌𝑓
𝜌𝑣𝜌𝑓𝑎𝑣𝑐
1/2
Where
Vt is the terminal velocity, m/s
W is the weight of the particle, kg
ρv and ρf are mass densities of the particles and fluids,
(kg s2)/m4
av is the projected area of the particle perpendicular to the
direction of motion, m2
c is the overall drag coefficient (dimensionless)

14. Drag coefficient
 When a particle is immersed in a
fluid current the forces acting on the
particle has been illustrated in Fig.
 If Fy is the drag force and FH is lift
force, then the resultant force, FR
may be calculated by resolving the
forces.
𝐹𝑟 = 𝐶𝐴𝑝
𝜌𝑓𝑣2
2
Where,
FR = resistance drag force or weight of particle at terminal velocity, kg C =
Overall drag coefficient
𝜌𝑓 = mass density of fluid Kgs2/m4,
Ap = projected area of the particle normal to direction of motion, m2
V = relative velocity between main body of fluid and material, m/s

15. The drag coefficient of the material and its resistance to
air flow depend upon,
 The bed thickness of the material,
 Type, shape and size of grain,
 The air velocity and
 Orientation and packing of the material.

16. Rheological properties
 The rheological properties may be defined as the science
which deals with the deformation and flow of the material
under action of the applied forces.
 Time is an important parameter during application of load to
the body. Therefore, in rheology three important parameters
such as force, deformation and time are used for
expressing the mechanical behaviour of the material.
Strain
 The unit change, due to force, in the size or shape of a
body referred to its original size or shape. Strain is a non-
dimensional quantity, but it is frequently expressed
centimeters per centimeter, m/m, mm/mm etc.

17. Stress
 It is defined as the intensity of a point in a body of the
internal forces or components of force that act on a given
plane through the point. Stress is expressed in force per
unit of area (Kg/mm2).
Compressive strength
 It is the maximum compressive stress which a material is
capable of sustaining. Compressive strength is calculated
from the maximum load during a compression test and the
original cross sectional area of the specimen.
Elastic Limit
 The greatest stress which a material is capable of
sustaining without any permanent strain remaining upon
complete release of the stress.

18. Modulus of elasticity
 It is the ratio of stress to corresponding strain below the
proportional limit.
Poisson’s ratio
 The absolute value of the ratio of transverse strain to the
corresponding axial strain resulting from uniformly
distributed axial stress below the proportional limit of the
material.
Tensile strength
 The maximum tensile stress that a material is capable of
sustaining.

19. Thank You