Lecture 7 – Moisture Relationships
Announcements
7/13/2017
BAE2023 Physical Properties of
Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
–Measuring moisture content
•Oven drying…most common
•Distillation, chemical reactions, electrical
resistance or capacitance, near infrared
spectroscopy, nuclear magnetic
resonance
•Variation due to how water is
bound…chemically or physically
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BAE2023 Physical Properties of
Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
–Sampling
•Grain probe or trier (trucks or barges)
•Diverter sampler (streams of material)
•Ellis cup (material on a belt)
•Samples divided by a Boerner
divider…100-200g samples
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BAE2023 Physical Properties of
Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
–Convection Oven Method
•ASAE Standard S352.1, grain and seeds
–Numbered dishes are heated for 1 hour
–Grain is placed in dishes and in oven
–Removed and placed in desiccator to be brought to
room temperature and weighed
–Heating times and temp vary by material
–Wheat, oats, rye…130°C, 19 hr, 22hr, or 16 hr
respectively (just an example)
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BAE2023 Physical Properties of
Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
–Chemical method
•Karl Fischer method: page 84
–Electrical method
•Moisture meters
•Grain capacitance/conductance meter
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BAE2023 Physical Properties of
Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
–Equilibrium Moisture Content (EMC)
•Material moisture content when equilibrium
occurs during the exchange of moisture
between material and air
–Equilibrium Relative Humidity
•RH of air when equilibrium occurs
–Relationship varies with temperature
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BAE2023 Physical Properties of
Biological Materials Lecture 6
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Moisture Relationships
Chpt 3, Pages 81-105
7/13/2017
BAE2023 Physical Properties of
Biological Materials Lecture 6
7
Moisture Relationships
Chpt 3, Pages 81-105
7/13/2017
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Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
Equivalent
Relative
Humidity,
%
7/13/2017
(40% seed oil content)
Temperature, °F
20
30
40
50
60
70
80
20
4.9
4.5
4.1
3.8
3.6
3.4
3.2
30
6.5
5.9
5.5
5.1
4.8
4.5
4.3
40
8.1
7.4
6.8
6.3
6.0
5.6
5.3
50
9.6
8.8
8.1
7.6
7.1
6.8
6.4
60
11.3
10.3
9.6
9.0
8.4
8.0
7.6
70
13.1
12.1
11.2
10.5
10.0
9.3
8.9
80
15.4
14.2
13.2
12.3
11.6
11.0
10.5
90
18.6
17.2
16.0
15.0
14.2
13.5
12.8
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Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
•Two equations for predicting EMC
–Henderson or modified Henderson Equation
–Chung-Pfost equation
•Each has 2 forms:
–EMC as a function of temperature and MCd
–MCd as a function of rel. humidity and
temperature
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Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
–Modified Henderson:
–Chung-Pfost:
•K, N, and C are constants specific to materials (Table 3.2,
pg 92)
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Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
–Modified Henderson:
–Chung-Pfost:
•A, B, E, F, K, N, and C are constants specific to materials
(Table 3.2, pg 92)
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Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
–When all you know is the % dry matter as fat
and % dry matter as nitrogen free extract (%
carb which does not include fiber), use this
equation from Vemuganti and Pfost:
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Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
–Example:
•Using the Modified Henderson and the ChungPfost Equations:
–Determine the moisture content of rough rice at 20°C
and 35% RH
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Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
–Example:
•Using the Modified Henderson and the ChungPfost Equations:
–If the air temperature is 22°C, what does the rh need
to be to dry corn to 15% MCw?
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Biological Materials Lecture 6
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Lecture 7 – Moisture Relationships
–Example:
•Compute the final moisture content after
thoroughly mixing 60 kg of 18% MC corn with 40
kg of 12% MC corn.
•Compute the final moisture content after mixing
30 kg of 18% MC corn with 40 kg of 12% MC Corn.
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Biological Materials Lecture 6
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