1. Physical Characteristics
Dr. Muanmai Apintanapong

2. Physical Characteristics
Considering either bulk or individual units of material.
Shape, size, volume, specific gravity surface area, bulk density and etc.
Size
Shape
Weight
Volume

3. Shape and size Inseparable in a physical object  =  (sh, s)
 = Index
sh = shape
s = size
Other applications
 =  (sh, s, o, p, f,…)
Y = b1X1+b2X2+b3X3+b4X4+b5X5

4. Seeds, grains, fruits and vegetables are irregular in shape
 important to know what criterion should be used to decide when adequate number of measurements has been made to define the form of object.
Griffith (1964) : related volume (V) to their axial dimension (a)
V = a1b1 a2b2 a3b3 … anbn
log V = b1 log a1 + b2 log a2 +….+ bn log an

5. Criteria for describing shape and size
Size : a representative dimension
In fruit and cereal: 3 main projected area
a = length
b = width
c = thickness

6. Average dimension
Arithmatic mean size
Geometric mean size
Size based on volume

7. Average dimension
Size based on surface area
Size based on projected area

8. Measuring Grain Dimension
Grain Type
Length (mm)
very long > 7.5
long > 6.5 < 7.5
medium >5.5 < 6.5
short < 5.5

9. Physical Properties>>shapeV
LWT αv
The concept of shape factor
Geometric dimensions (L,W,T) of various objects are plotted against their volumes, surface areas or projected areas
The slope of regression line yields shape factor (α) SA
(LWT)2/3
αSA Ap
(LWT)2/3
αAp

10. Example
Axial dimension (cm)
Weight
(g)
Volume
(cm3) a b c
apples
7.0
6.76
5.64
145.5
180.3
potatoes
8.2
7.2
5.3
204.0
184.0
tomatoes
6.45
5.92
4.72
127.3
126.2
Determine: v, density, equivalent diameter of sphere, average diameter, geometric mean diameter

11. Charted standards
Compare longitudinal and lateral cross section with the shapes listed on a charted standard

12. Roundness Measure of sharpness of the corners of the solid
Ap = largest projected area in natural rest position
Ac = area of smallest circumscribing circle

13. Roundness
r = radius of curvature as defined in figure
R = radius of maximum inscribed circle
N = total number of corners summed in numerator

14. Roundness
r = radius of curvature of the shapest corner
R = mean radius of object

15. Sphericity
di = diameter of the largest inscribed circle
dc = diameter of the smallest circumscribed circle

16. de = diameter of a sphere of same volume of object
Sphericity dc
de = diameter of a sphere of same volume of object
dc = diameter of the smallest circumscribed sphere (usually the longest diameter of object)

17. Sphericity a = longest intercept b = longest intercept normal to a
c = longest intercept normal to a and b

18. Shape factor ()

20. Measurement of axial dimension
Use photographics enlarger to determine a, b, c
Use shadowgraph

21. Resemblance to geometric bodies
Shape can be approximated by one of the following standard geometric shapes:
Prolate spheroid
Oblate spheroid
Right circular cone or cylinder

22. Resemblance to geometric bodies
Prolate spheroid
Volume
Surface area
a, b = major & minor semi-axes of ellipse of rotation
e = eccentricity
V = volume
S = surface area
V =
A prolate spheroid is a spheroid in which the polar diameter is longer than the equatorial diameter.
S =

23. Resemblance to geometric bodies
Oblate spheroid
Volume
Surface area
a, b = major & minor semi-axes of ellipse of rotation
e = eccentricity
V = volume
S = surface area
V =
An oblate spheroid is a rotationally symmetric ellipsoid having a polar axis shorter than the diameter of the equatorial circle whose plane bisects it.
S =

24. Resemblance to geometric bodies
Frustum of right cone
Volume
Surface area
r1 & r2 = radii of base & top
h = altitude
A cone that has its apex aligned directly above the center of its base.
V =
S =

25. Right Circular Cylinder
A right cylinder with bases that are circles.

26. Resemblance to geometric bodies
Estimation of V and S in this manner should be corrected.
Correction factor is determined by finding actual volume and surface area experimentally and establish correction factor for the typical shape of each variety of product.

27. Average projected area
Camera set up for recording the criterion area (above left) of fruits and vegetables for several orientations.

29. Average projected area
Based on Theory of Convex body (Bannesen and Fenchel, 1948)
Sphere:
Nonsphere:

30. Polya & Szega (1951)
Assume averaged projected area of convex body = ¼ of surface area

33. Volume and Density
Platform balance method: for large objects such as fruits and vegetables

34. Example
Assuming a specific gravity of 1.0 and a weight density of 62.4 lb/ft3 for water, using a platform scale method, the volume and specific gravity of an apple was determined as follows:
Weight of apple in air = lb
Weight of container+water = 2.24 lb
Weight of container+water+apple submerged = 2.61 lb
Weight of displaced water = = 0.37 lb

35. Specific gravity balance
For smaller objects such as small fruits, peas and beans, kernels of corn, etc.

36. Specific gravity balance
If solid is heavier than water:
If solid is lighter than water (attach another solid as sinker)
Wa = wt. in air
Ww = wt. in water

37. Specific gravity gradient tube
Fast and accurate
Ex: toluene & CCl4 (sp. gr )
Measure the height after object reaches equilibrium and calculated and compared with calibration curve.

38. Air comparison pycnometer
The density of a solid in any form can be measured at room temperature with the gas comparison pycnometer. The volume of a substance is measured in air or in an inert gas in a cylinder of variable calibrated volume. For the calculation of density one mass measurement is taken after concluding the volume measurement.

39. Air comparison pycnometer

40. Pycnometer method Specific gravity bottle and toluene
Toluene (C6H5CH3) has the advantages of:
Little tendency to soak into the kernel
Low surface tension, enabling it to flow smoothly over kernel
Little solvent action on constituents of kernel especially fats and oils
High boiling point
Not changing its specific gravity and viscosity on exposure to atmosphere
Having low specific gravity

41. Pycnometer method

42. Example
Consider the volume measurement for a sample of 16 corn kernels coated with Pliabond
Weight of sample = g
Weight of pycnometer = g
Weight of pycnometer+toluene = g
Weight of pycnometer+toluene+sample = g
Weight of pycnometer+water = g

43. Porosity
Void volume or pore volume (empty space) relative to total volume

44. Porosity tank

46. Example
To determine the porosity of dry shelled corn, tank 2 of the apparatus is filled with a sample of this corn to a bulk density of 47 lb/ft3. The pressure readings were P1 = 15.2 and P2 = 10.4 in Hg

47. Porosity

48. Porosity is also referred to as packing factor (PF):

49. Porosity and bulk density

51. Weight and surface area

52. Surface area
Leaf and stalk surface area
Light planimeter
Indirect estimation (projected area)
Surface coating method
Estimated by the weight of coating material
Material is coated on grains and glass beads of known surface area (control).
Air permeability method

53. Shape, Size and Area Using image analysis
The image analysis setup consists of a color CCD camera and a circular lighting chamber connected to a host Pentium II 400 MHz computer.

54. Top view of the Image Analysis Set up

55. CCD Camera
Illumination Chamber

56. Image Analysis Software
Two image analysis software are available for extracting the dimensional feature of rice kernels
1. Image Tool 2: This program was developed at the University of Texas Health Science center at San Antonio, Texas and available from the internet (
2. Particle Image Analysis: This program was developed by Procure Vision AB Ltd., Stockholm, Sweden and the evaluation version is available from the internet (