Professional Engineering Review Session Materials Properties (5.D.)

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Professional Engineering Review SessionMaterials
Properties (5.D.)

• Steve Hall, Ph.D., P.E.
• shall5_at_lsu.edu Louisiana State University
  AgCenter

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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 4

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References

• PE Review Manual FE Review Manual
• Ma, Davis, Obaldo, Barbosa, 1998. Engineering
  Properties of Foods and Other Biological
  Materials, ASAE.
• Mohsenin,1986. Physical Properties of Materials
• Rao, Rizvi, Datta, 2005. Engineering Properties
  of Foods.
• Merva, 1995. Physical Principles of the Plant
  Biosystem.
• Reynolds and Richards, 1996. Unit Operations and
  Processes in Environmental Engineering.

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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 (SE)
• Hellevang, AE-84, Temporary grain storage,
• http//www.ag.ndsu.edu/publications/landing-pages/
  crops/temporary-grain-storage-ae-84

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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)

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Rheology The study of deformation and flow of
matter (especially interesting in agricultural
and biological materials)
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Stress/Strain at the atomic level
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Stress/Strain

• Stress s Fnormal to area/A
• Shear Stress t Fparallel to area/A
• Strain edL/Lo m/m or
• Youngs modulus E s Ee or E s/e
• For bar, d PL/AE or FL/AE

Tension compression
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Stress-strain
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Stress/strain for steel and rubber a) linearity
(E constant?) b) average E typically lower in
biomaterials
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Hair
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Hysteresis cycles of a rubber
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Stress vs. Conventional StrainConventional
F/AoriginalTrue Stress F/Aactual
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Reminder Stress/Strain

• Stress s Fnormal to area/A
• Shear Stress t Fparallel to area/A
• Strain edL/Lo m/m or
• Youngs modulus E s Ee or E s/e
• For bar, d PL/AE or FL/AE

Tension compression
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Sample problem

• A steel bar with known dimensions is subjected to
  an axial compressive load. The modulus of
  elasticity and Poissons ration are known. What
  is the final thickness of the bar?
• A) 19.004mm
• B) 19.996mm
• C) 20.00mm
• D) 20.004mm

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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
  Poissons ration are known. What is the final
  thickness of the sample?

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Stress-Strain Models
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Creep behavior of cheddar cheese
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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?

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Solution

• From the graph, strain after 2 hours (120 min) is
  approx 0.09. (be careful with extrapolation, but
  could use eqn for longer times).
• Original dimensions 100 x 100 x 100mm
• Strain .09mm/mm so 100-100(.09) 91mm tall
• Poissons ratio 0.3 so expansion (in width) .03mm
• 103x103x91mm tall

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Stress relaxation of potato tissue
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Stress/Strain (estimate E)A (chord/secant) B
secant C tangent apparent modulus
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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

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Shear modulus and viscosity
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Newtonian type Fluids

• Viscosity m is resistance to flow
• F/A t m du/dy
• Kinematic viscosity is viscosity over density
• u m/r

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Values of Viscosity for Food Products and
Agricultural Materials Which are Newtonian
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Arrhenius Relationship

• µ Viscosity (Pa s)
• µ?A Constant (Pa s)
• EaActivation Energy (Kcal g-Mole)
• RGas Constant (kcal/g-mole ºK)
• TAbsolute Temperature (ºK)

• Definition Viscosity of Fluid Decreases with
  Temperature (Change is typically 2 per Degree
  Celsius)

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Behavior of Time-Dependent Fluids

• A Apparent Viscosity as a function of time
• B Shear Stress as a function of shear rate

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Moisture impacts rheology
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Break stretch (but dont strain too much!)
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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.

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D241.4 food propertiesbulk density, moisture
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D241.4 grain properties
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D243.3 thermal properties of grain
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EP545 Loads exerted by free-flowing grain on
shallow storage structures
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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

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Hellevang

• Overview of temporary grain storage (free
  reference http//www.ag.ndsu.edu/publications/land
  ing-pages/crops/temporary-grain-storage-ae-84)
• 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 20
• Corn (shelled) 23Oats 14
• Grain Sorghum 22
• Soybeans 21
• Sunflower (non-oil) 9
• Sunflower (oil) 12
• Durum wheat 26HRS wheat 24

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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)

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Particle size distribution
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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

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Solution use Hellevang

• Answer is B

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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

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Solution

• Look up in Hellevang table!
• Hellevangs 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!

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Break!

• Stretch, drink of water, short break

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Water in Biological Materials

• Steve Hall, Ph.D., P.E.Louisiana State
  University AgCenter

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Moisture impacts rheology
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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, tinfinity
• Hysteresis nonlinearities in MC curves

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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)

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D245.5

• To convert from dry basis to wet basis
• To convert from wet basis to dry basis

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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
• Mwb (wet basis) water mass/total wet mass
• 7/10 70
• Mdb (dry basis) water mass/dry mass 7/3
  233
• Or (233-70)/70 or 200 error! BE CAREFUL!!

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D245.5

• Isotherm data (used in drying calculations)
• In table format or graphical format

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aw pw/pwpure
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Availability of water for microbial activity (van
den Berg and Bruin)
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Equilibrium Moisture Content
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Equilibrium Moisture Content Wheat
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Corn Hysteresis of EMC
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EMC Curves
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Estimating MC Biol. Matls

• 1-rhe-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.

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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

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Use equation, careful of units
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Expansion due to moisture
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Psychrometrics

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

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Psychrometric Chart
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Psychrometrics
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Steps to solve Psychrometrics

• Read carefully
• What stays constant
• Follow lines
• Read carefully/interpolate
• Make calculations
• One step at a time, then repeat

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Psychrometrics (constants)
Volume (density)
Humidity ratio (water/air mass)
Saturation (dewpoint)
Enthalpy (wet bulb)
(Dry bulb) Temperature
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PsychrometricsWhat stays constant?(what line
do I follow?) Temp (dry bulb)Saturation (below
dewpoint)humidity ratio (kg/kg dry air)Other
options as stated
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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?

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Psychrometrics
Dewpt (66)
88RH
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Example

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

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Psychrometrics
Diff .002 lbwater/lb dry air
.0094 lbwater/lbdry air
.0074 lbwater/lbdry air
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How much water to mist in?

• Difference 0.002 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 0.258 kg water or .258liters (1 cup of water!)

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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)

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ReminderSteps to solve Psychrometrics

• Read carefully
• What stays constant?
• Follow lines
• Read carefully/interpolate
• Make calculations
• One step at a time, then repeat

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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 nights sleep
• Eat breakfast

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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

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Thank You!