World Grain - November 2022 - 58

GRAIN OPERATIONS: DETECTING SPOILAGE WITH TEMPERATURE SENSORS
Table 1
Date
1-Jan
8-Jan
15-Jan
22-Jan
29-Jan
5-Feb
Sensor 1
39.2
39.2
39.2
39.2
39.2
39.2
Sensor 2
39.2
39.2
39.4
39.6
40.0
40.6
Sensor 3
39.2
39.2
39.2
39.2
39.2
39.2
Sensor 4
39.2
39.2
39.2
39.2
39.2
39.2
Predicted temperature readings over a five-week period as a
result of self-heating corn increasing by 5° F per week 3 feet from
sensor 2. Temperatures are recorded in degrees Fahrenheit.
Bold italicized temperatures show changes by at least 1 degree F over time.
the readings from their temperature cables weekly during
warm weather periods and biweekly during cold
weather periods and decide the potential cause of any
unexplained temperature increases.
Grain temperatures may change slowly over time
throughout the storage period but generally fall into predictable
patterns. Grain warms or cools from the outside
wall or headspace into the grain mass, and at a relatively
consistent rate given grain is a pretty good insulator.
Figure 1
65
60
55
50
45
40
Temperature cable readings
source
1 foot
2 feet
3 feet
6 & 9 feet
A common criterion used by grain managers is that if
1
2
Weeks
Predicted temperature readings over time for sensors 1 foot (0.3
m), 2 feet (0.6 m), 3 feet (0.9 m), 6 feet (1.8 m), and 9 feet (2.7 m)
away from the self-heating corn compared to the temperature at
the source of self-heat over a five-week period in the middle of an
Iowa winter.
spores on grain kernel surfaces, or spores that have penetrated
into broken or cracked kernels, will multiply. The biological activity
of molds consumes dry matter in grain (starch), produces heat,
releases CO2
, and when allowed to continue will result in grain
crusting. In severe cases, mold development can lead to mycotoxin
contamination.
Detection of self-heating grain
When heat is generated by biological mold activity, the heat is transferred
mostly through conduction from kernel to kernel and to a lesser
extent by natural convection through the grain mass. For self-heating
grain to be detected, the heat must be transferred far enough that
a temperature sensor on a temperature cable can detect the change
in temperature. In practice, this requires grain managers to review
58
3
4
5
grain begins to change by more than 1° F per week over
two to three weeks in a row, action to maintain grain
quality may need to be taken. To simplify this task,
temperature cable readings typically are organized by
sensor and time stamp.
Having all readings from one sensor node lined up
by date makes trends over time easier to interpret (see
example shown in Table 1, upper left). However, a
grain manager can only act as quickly as the temperature
cables can detect self-heating.
Modeling the heat transfer of
self-heating grain
A computer model developed by the authors at Iowa
State University was utilized to predict the heat transfer
of self-heating grain in a bin. For this example, we evaluated
corn stored in a bin into winter in a US Midwest
location. Initial corn temperature was uniform at 39.2°
F (4° C) after assuming successful aeration cooling. A
hot spot was allowed to develop that increased in temperature
by 5.4° F (3° C) per week starting Jan. 1.
To the left is a temperature cable readout generated
from the model. While the claims made by temperature
cable manufacturers vary, sensors generally are
spaced out 6 to 8 feet (1.8 to 2.4 m) so we examined
the response time of a sensor 3 ft (0.9 m) from the selfheating
grain.
In Table 1, sensor 2 is 3 feet (0.9 m) from the selfheating
grain. At this distance, it takes two weeks before
a change is detected. However, this change is only
November 2022 / World Grain / World-Grain.com
The number and placement of
sensors, and the interpretation
of sensor readings, are key to
effectively monitoring conditions
in a stored grain mass and
managing optimal windows
of aeration based on real-time
weather data.
Temperature (°F)
Source: Iowa State University
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