1. Professional Engineering Review Session Materials Properties (5.D.)
Steve Hall, Ph.D., P.E.
Louisiana State University AgCenter

2. Current NCEES Topics Primary coverage: Exam %
V. D. Materials Properties; Bulk Solids 4%
Overlaps with:
I. D. 1. Mass and energy balances ~2%
I. D. 2. Applied psychrometric processes ~2%
V. C. Mass transfer between phases %

3. References PE Review Manual; FE Review Manual
Ma, Davis, Obaldo, Barbosa, Engineering Properties of Foods and Other Biological Materials, ASAE.
Mohsenin,1986. Physical Properties of Materials
Rao, Rizvi, Datta, Engineering Properties of Foods.
Merva, Physical Principles of the Plant Biosystem.
Reynolds and Richards, Unit Operations and Processes in Environmental Engineering.

4. Standards
D241.4: Density, specific gravity and mass-moisture relationships of grain for storage
D243.e: Thermal properties of grain and grain products
D245.5: Moisture relationships of plant-based ag products
EP545: Loads exerted by free-flowing grain on shallow storage structures (S&E)
Hellevang, AE-84, Temporary grain storage,

5. Specific Topics Rheology Density, specific gravity
Moisture content in ag and food products
Thermal properties of grain and grain products
Loads on structures from grain/flowing products
Bonus: Psychrometrics (moisture 5D; ID Psychrometrics)

6. Rheology: The study of deformation and flow of matter (especially interesting in agricultural and biological materials)

7. Stress/Strain at the atomic level

9. Stress/Strain Stress s = Fnormal to area/A
Shear Stress t = Fparallel to area/A
Strain e=dL/Lo [m/m; or %]
Young’s modulus E: s = Ee or E = s/e
For bar, d = PL/AE or FL/AE
Tension
compression

10. Stress-strain

11. Stress/strain for steel and rubber. a) linearity (E constant. )
Stress/strain for steel and rubber a) linearity (E constant?) b) average E typically lower in biomaterials

12. Hair

13. Hysteresis cycles of a rubber

14. Stress vs. Conventional Strain Conventional: F/Aoriginal True Stress: F/Aactual

15. Reminder: Stress/Strain
Stress s = Fnormal to area/A
Shear Stress t = Fparallel to area/A
Strain e=dL/Lo [m/m; or %]
Young’s modulus E: s = Ee or E = s/e
For bar, d = PL/AE or FL/AE
Tension
compression

16. Sample problem
A steel bar with known dimensions is subjected to an axial compressive load. The modulus of elasticity and Poisson’s ration are known. What is the final thickness of the bar?
A) mm
B) mm
C) 20.00mm
D) mm

18. Sample problem, food materials emphasis
A block of cheese with known dimensions is stacked and thus subjected to an axial compressive load. The modulus of elasticity and Poisson’s ration are known. What is the final thickness of the sample?

20. Stress-Strain Models

21. Creep behavior of cheddar cheese

22. Sample problem, materials emphasis
A block of cheese with known dimensions is stacked and thus subjected to an axial compressive load. After being stacked for 2 hours, what is the final thickness of the sample?

23. Solution
From the graph, strain after 2 hours (120 min) is approx (be careful with extrapolation, but could use eqn for longer times).
Original dimensions: 100 x 100 x 100mm
Strain .09mm/mm so (.09) = 91mm tall
Poisson’s ratio 0.3 so expansion (in width) .03mm
103x103x91mm tall

24. Stress relaxation of potato tissue

25. Stress/Strain (estimate E) A (chord/secant); B secant; C tangent apparent modulus

27. Rheological Behavior of Fluids
A: Shearing of a Newtonian Fluid
B: Shear Stress Versus Shear Rate for Newtonian, Pseudoplastic (Shear Thinning), and Dilantant (Shear Thickening), Plastic, and Casson-Type Plastic Fluids

28. Shear modulus and viscosity

29. Newtonian type Fluids Viscosity: m is resistance to flow
F/A = t = m du/dy
Kinematic viscosity is viscosity over density:
u = m/r

30. Values of Viscosity for Food Products and Agricultural Materials Which are Newtonian

31. Arrhenius Relationship:
Definition: Viscosity of Fluid Decreases with Temperature (Change is typically 2% per Degree Celsius)
µ =Viscosity (Pa s)
µф=A Constant (Pa s)
Ea=Activation Energy (Kcal g-Mole)
R=Gas Constant (kcal/g-mole ºK)
T=Absolute Temperature (ºK)

32. Behavior of Time-Dependent Fluids
A: Apparent Viscosity as a function of time
B: Shear Stress as a function of shear rate

33. Moisture impacts rheology

34. Break stretch (but don’t strain too much!)

35. Bulk Density
Bulk density is a property of particulate materials like sand or grain. It is defined the mass of many particles of the material divided by the volume they occupy.
Bulk Density = M/V [kg/m3]
The volume includes the space between particles as well as the space inside the pores of individual particles.

36. D241.4: food properties: bulk density, moisture

37. D241.4: grain properties

38. D243.3: thermal properties of grain

39. EP545: Loads exerted by free-flowing grain on shallow storage structures

40. EP545
Total equivalent grain height: taken as the “average” grain height if the top grain surface is not horizontal (may not be, angle of repose)
Design approach, shallow grain holding structures:
Determine material properties (bulk density, angle of repose, coefficient of friction)
Use properties to calculate total equivalent grain height
Calculate static pressures (static vertical pressure at any point, static lateral pressure, and vertical pressure on floor)
Calculate resultant wall forces (resultant lateral force, resultant shear force)
Ex., Lateral force per unit length PH = LH2/2 where
L is the lateral pressure (function of depth z) and H is the equivalent grain height
Lateral pressure L(z) = kV(z)
Where L(z) = lateral pressure at grain depth z, psf (pounds per square foot)
k = ratio of lateral to vertical pressure, dimensionless and assumed to be 0.5
V(z) = vertical pressure at equivalent grain depth z, psf
V(z) = Wg where W is the bulk density (lb/ft3), g is acceleration to due gravity

41. Hellevang
Overview of temporary grain storage (free reference
The pressure grain exerts per foot of depth is called the equivalent fluid density
Table 1. Approximate equivalent fluid density of some peaked grains.
Crop Equivalent Fluid Density lb/cu. ft
Barley
Corn (shelled) Oats
Grain Sorghum 22
Soybeans
Sunflower (non-oil)
Sunflower (oil) 12
Durum wheat HRS wheat

42. Particle size distribution
Different for different materials!
Good reference: Chapter 35, CE manual, soil properties and testing
Sieve sizes and corresponding opening sizes (ASTM)
Typical particle size distribution (for soil):
Remember statistics for particle size distribution
Research on particle size distributions of nanoparticles
Normal distribution
Mean (“average”) particle size
Measure of dispersion of particle size (standard deviation, for example)

43. Particle size distribution

44. Sample questions
A building with an 8-foot high wall is storing grain. Grain was placed into the storage building and leveled until it is within 6 inches of the top of the wall. The grain density is 60 pounds per bushel. The lateral force per unit length at the base of the wall is most nearly
(a) 638, (b) 672, (c) 717, (d) 1360

45. Solution: use Hellevang
Answer is B

46. Sample questions
If corn is treated as a non-cohesive granular material (shelled), the equivalent fluid density (pounds per cubic foot) is most nearly:
(a) 22
(b) 28
(c) 35
(d) 56

47. Solution Look up in Hellevang table!
Hellevang’s table for shelled corn: 23 #/sqft
Answer is A
Do not be deterred by the fact that the values are not exactly the same! PE questions are constructed to accommodate minor differences in tabulated values!

48. Break!
Stretch, drink of water, short break…

49. Water in Biological Materials
Steve Hall, Ph.D., P.E. Louisiana State University AgCenter

50. Moisture impacts rheology

51. Definitions Mwb (wet basis) = water mass/total wet mass
Mdb (dry basis) = water mass/dry mass
aw = pw/pwpure
RH = water in a gas/maximum possible water at T
Equilibrium MC = MC at RH, T, t=infinity
Hysteresis: nonlinearities in MC curves

52. D245.5: moisture relationships
Moisture content wet basis
Where m or mwb = wet basis moisture content (decimal)
Wm = mass of moisture
Wd = mass of dry matter
Moisture content dry basis
Where M or Mdb = dry basis moisture content (decimal)
Dry basis moisture content can exceed 1 (or 100%)

53. D245.5 To convert from dry basis to wet basis:
To convert from wet basis to dry basis:

54. Example: MC Wheat: Pan mass: 10 g; wheat + pan = 110 g
Dried weight = 100 g
Mwb (wet basis) = water mass/total wet mass
= 10g/100g = 10%
Mdb (dry basis) = water mass/dry mass
= 10g/90g = 11% or (11-10)/10 = 0.1 or 10% error
Apple: 10 g wet; 3 g dry
= 7/10= 70%
Mdb (dry basis) = water mass/dry mass = 7/3 = 233%
Or (233-70)/70 or 200+% error! BE CAREFUL!!

55. D245.5 Isotherm data (used in drying calculations)
In table format or graphical format

56. aw = pw/pwpure

57. Availability of water for microbial activity (van den Berg and Bruin)

58. Equilibrium Moisture Content

59. Equilibrium Moisture Content: Wheat

60. Corn: Hysteresis of EMC

61. EMC Curves

62. Estimating MC: Biol. Matls
1-rh=e-KTMn .
where rh relative humidity, decimal
T = absolute temperature,°R
M = equilibrium moisture content, % d.b.
k and n are are constants as specified in the following table.

63. Example Problem
A sealed container is filled with soybeans at 20% moisture (w.b.) Estimate the relative humidity of the interseed air. The temperature is 60 degrees F.
A) 15%
B) 20%
C) 55%
D) 85%

64. Use equation, careful of units

65. Expansion due to moisture

66. Psychrometrics
Moisture, RH, Temp, Enthalpy (energy) as related to moisture in the atmosphere or in enclosed spaces (e.g. buildings)

67. Psychrometric Chart

68. Psychrometrics

69. Steps to solve Psychrometrics
Read carefully
What stays constant
Follow lines
Read carefully/interpolate
Make calculations
One step at a time, then repeat

70. Psychrometrics (constants)
Volume
(density)
Humidity ratio
(water/air mass)
Saturation
(dewpoint)
Enthalpy
(wet bulb)
(Dry bulb) Temperature

71. Psychrometrics What stays constant. (what line do I follow
Psychrometrics What stays constant? (what line do I follow?) Temp (dry bulb) Saturation (below dewpoint) humidity ratio (kg/kg dry air) Other options as stated

73. Example Day ends with 70% RH at 80F Temp drops to 70F
(what stays constant?) (rh, sat?)
Is there dew?
What is the dewpoint?
If not, what is the new RH?

74. Psychrometrics
Dewpt
(66)
88%RH 70 80

75. Example 100m3 Greenhouse: T = 70F, RH is 40%.
How much water (mist) to add to reach 50%RH?
Assume: density of dry air is 1/800th of water or about 1.29kg/m3
Assume: temperature remains constant
(State your assumptions!)

76. Psychrometrics Diff = .002 lbwater/lb dry air{ .0094 lbwater/lbdry air

77. How much water to mist in?
Difference = lb water/lb dry air
So what is the amount of water to add?
Based on volume
Assume a 100 m3 greenhouse.
Still need an estimate of mass of dry air…
Assume 1.29kg/m3 *100m3 = 129 kg
129kg air*(0.002kg water/kg dry air) (why?)
Or kg water or .258liters (~1 cup of water!)

78. What other questions can you ask as biological engineers?
Air conditioning (removes water, change temperature) humans
Dehumidifier (removes water) humans
Rain adds water
Plant transpiration adds water plants
Sun adds energy/temp plants/animals
Radiation at night removes energy/temp
Drying processes or adding moisture (bacterial, biomed, bioprocess)

79. Reminder: Steps to solve Psychrometrics
Read carefully
What stays constant?
Follow lines
Read carefully/interpolate
Make calculations
One step at a time, then repeat

80. Conclusions Remember basic definitions Careful with Units
Use what you are given
Practice with your references
Keep a sense of time
Keep learning
Get a good night’s sleep
Eat breakfast

81. Any questions on V-D? Tips:
Have a table or set of tables with material properties handy
Additional material property references:
Johnson, Biological Process Engineering, has many material property charts (density, specific heat, thermal conductivity, thermal diffusivity, etc.)
Geankoplis, Transport Processes and Separation Process Principles (Includes Unit Operations), 4/e
This area overlaps with many others
Know how to convert between wet and dry basis moisture contents!
Remember common sense and statistics

82. Thank You!