Title: Professional Engineering Review Session Materials Properties (III.E; Overlap with III.D, I, J)
1Professional Engineering Review SessionMaterials
Properties (III.EOverlap with III.D, I, J)
- Steve Hall, Ph.D., P.E.
- shall5_at_lsu.edu Louisiana State University
AgCenter
22016 is second year of new exam
- Some Overlap New Material
- Preparation is Important!!
- A) Exam Preparation Suggestions
- B) Specific Information on Materials
3Exam Preparation Suggestions
- Congratulations on Being Here Today!
- You are doing exam prep
- Ideally give yourself 3-6 months of prep time
- Ideally have set times every week
- Suggestions to follow
4Location Location Location
- Away from distractions (work, family, etc.)
- Quiet
- Your space (books, references)
- Comfortable (space on a table water to drink)
- Set time and place
5A Time for Everything
- My example 6-9 PM M-Th (12 hours per week)/3
months - Table in room my space
- Food (eat and study)
- Water
- Books in a Box (develop references)
6What to Study?
- This webinar series covers a bit
- Look through NCEES Info http//ncees.org/exams/pe-
exam/ - Get Specific Detailed Parts/Areas
- cdn.ncees.org/wp-content/uploads/2012/11/Ag_Bio-Ap
r-20151.pdf
7Some titles on Ag/Bio PE
- Common System Applications (pumps, energy,
graphics, safety, stress-strain) - Natural Resources and Ecology (ecology, erosion,
irrigation, nutrients, soil/water) - Process Engineering (kinetics, transport,
properties, reactors, mass balances) - Facilities (animal, plant, structural)
- Machines (power, motors, engines, components,
models)
8Choose your Strengths
- Practice makes perfect
- Find areas you like
- Practice until you are perfect
- Then Cover Breadth and get good
- Skip a little if you really struggle
9Arrange References
- FE Review Manual
- Textbooks
- ASABE References
- Know/mark each one
- Use them as you practice
- Develop favorites (1 top ref 5 faves)
10Stick with it!
- Get friends/colleagues/family to support
- Give me time to study
- I will spend more time with you after April
- Take it once and pass it!!
11Funny Story (?)
- As we were settling into the exam, another
examinee said What time is it for you? Turning,
I listened my fourth my fifth. I asked
where do you work?. - At the nuclear plant came the reply.
- Take the test once and get it done!
12This Review FocusNCEES Topics
- Primary coverage Materials
- III. E. Physical and chemical properties of
biological materials - Overlaps with
- III.D. Mass transfer between phases
- III.I. Applied psychrometric processes
- I.L (energy transfer, esp. latent heat and phase
change) - III.J. Mass balances
-
-
-
13References
- 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.
14Standards
- 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
15Specific 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
-
16Rheology The study of deformation and flow of
matter (especially interesting in agricultural
and biological materials)
17Stress/Strain at the atomic level vs. macroscopic
(bulk) properties
18Rheology Describing Materials
19Stress/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 (E can
vary) - For bar, d PL/AE or FL/AE
Tension compression
20Stress-strain (offsets, hysteresis)
21Stress/strain for steel and rubber a) linearity
(E constant?) b) average E typically lower in
biomaterials
22Hair
23Hysteresis cycles of a rubber
24Stress vs. Conventional Strain (steel/conventional
materialsConventional F/AoriginalTrue
Stress F/Aactual
25Reminder 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
26Sample 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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28Sample 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 ratio are known. What is the final
thickness of the sample?
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30Stress-Strain Models
31Creep behavior of cheddar cheese over time
32Sample 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?
33Solution
- 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
34Stress relaxation of potato tissue
35Stress/Strain (estimate E)A (chord/secant) B
secant C tangent apparent modulus
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37Break stretch (but dont strain too much!)
38Rheological 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
39Shear modulus and viscosity
40Newtonian type Fluids
- Viscosity m is resistance to flow
- F/A t m du/dy
- Kinematic viscosity is viscosity over density
- u m/r
41Values of Viscosity for Food Products and
Agricultural Materials Which are Newtonian
42Arrhenius 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)
43Behavior of Time-Dependent Fluids
- A Apparent Viscosity as a function of time
- B Shear Stress as a function of shear rate
44Moisture impacts rheology
45Bulk 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.
46D241.4 food propertiesbulk density, moisture
47D241.4 grain properties
48D243.3 thermal properties of grain
49EP545 Loads exerted by free-flowing grain on
shallow storage structures
50EP545
- 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
51Hellevang
- 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
52Particle 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)
53Particle size distribution
54Sample 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
55Solution use Hellevang
56Sample 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
57Solution
- Look up in Hellevang table!
- Hellevangs table for shelled corn 23 /sqft
- Answer is A
- Crop Equivalent Fluid Density lb/cu. ft
- Barley 20
- Corn (shelled) 23Oats 14
- 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!
58Break!
- Stretch, drink of water, short break
59Water in Biological Materials
- Steve Hall, Ph.D., P.E.Louisiana State
University AgCenter
60Moisture impacts rheology
61Definitions
- 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
62D245.5 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)
63D245.5
- To convert from dry basis to wet basis
- To convert from wet basis to dry basis
64Example 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!!
65D245.5
- Isotherm data (used in drying calculations)
- In table format or graphical format
66aw pw/pwpure
67Availability of water for microbial activity (van
den Berg and Bruin)
68Equilibrium Moisture Content
69Equilibrium Moisture Content Wheat
70Corn Hysteresis of EMC
71EMC Curves
72Estimating 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.
73Example 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
-
74Use equation, careful of units
75Expansion due to moisture
76Psychrometrics
- Moisture, RH, Temp, Enthalpy (energy) as related
to moisture in the atmosphere or in enclosed
spaces (e.g. buildings)
77Psychrometric Chart
78Psychrometrics
79Steps to solve Psychrometrics
- Read carefully
- What stays constant
- Follow lines
- Read carefully/interpolate
- Make calculations
- One step at a time, then repeat
80Psychrometrics (constants)
Volume (density)
Humidity ratio (water/air mass)
Saturation (dewpoint)
Enthalpy (wet bulb)
(Dry bulb) Temperature
81PsychrometricsWhat 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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83Example
- 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?
84Psychrometrics
Dewpt (66)
88RH
80
70
85Example
- 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!)
86Psychrometrics
Diff .002 lbwater/lb dry air
.0094 lbwater/lbdry air
.0074 lbwater/lbdry air
87How 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!)
88What 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)
89ReminderSteps to solve Psychrometrics
- Read carefully
- What stays constant?
- Follow lines
- Read carefully/interpolate
- Make calculations
- One step at a time, then repeat
90Conclusions
- 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
91 - 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
92Thank You!