World Grain - April 2022 - 46

GRAIN OPERATIONS
Temperature cable placement
Location of cables is important in monitoring grain during the aeration and storage periods
by Dirk Maier and Jordan Wright
Monitoring the temperature, moisture content and carbon dioxide
(CO2
levels. Still, the complexities of stored grain ecosystems
) levels in stored grain is essential to maintaining
quality. Aeration with ambient air is the most common method
used to manage grain temperature, moisture content, and
CO2
make effective monitoring and optimal management challenging,
especially as storage bins (silos) increase in size.
Temperature and relative humidity sensors installed on cables
and placed in the stored grain mass are routinely used to
track grain mass temperature and moisture content. Carbon
dioxide sensors can be placed in the plenum and headspace
below and above the stored grain mass, respectively, to track
the onset of spoilage due to biological activity from molds
and insects.
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.
The second article in this series focuses on the placement
of temperature cables to effectively monitor the grain quality
during the aeration and storage periods.
Temperature monitoring during aeration
Temperature is the key factor for monitoring the progress of
an aeration front advancing through a grain mass during the
cool-down period. In a cored and near-level surface grain
mass, airflow is pretty much uniform and thus a cooling front
will move uni-directionally upward (or downward). When
the grain mass remains peaked, airflow is no longer uniform
and thus a cooling front will move more slowly through the
uncored and deeper center and faster through the shallower
periphery of the grain mass.
Nevertheless, airflow moves uni-directionally upward (or
downward) and not sideways through the grain mass. For a
typical design airflow rate of 0.1 cfm/bu (0.11 m3
/min/MT),
a cooling front will require a minimum of about 150 hours
to advance through the grain mass. At a typical temperature
46
sensor spacing of 6 feet (2.1 m) along a cable, the advancing
cooling front would move past a new layer of sensors about
every 15 hours if grain depth is 60 feet (60 feet/150 hours =
0.4 feet/hour; 6 feet/0.4 feet/hour = 15 hours) and every 10
hours if grain depth is 90 feet (90 feet/150 hours = 0.6 feet/
hour; 6 feet/0.6 feet/hour = 10 hours).
Thus, sensor spacing along a cable should consider airflow
rate, grain depth, and the stored grain manager's preference for
tracking cooling front advancement through the grain mass. For
example, if a stored grain manager wanted to check cooling
front progress twice a day (every 12 hours), then optimum sensor
spacing along cables in a 60 foot and 90 foot deep grain
mass would be about 5 feet (5 feet/0.4 feet/hour = 12.5 hours)
and 7 feet (7 feet/0.6 feet/hour = 11.7 feet), respectively.
On the other hand, if temperature sensors were spaced 3
feet (0.91 m) along a cable, and airflow rate was as high as 1
cfm/bushel (1.1 m3
/min/MT), as is typical in an on-farm drying
bin, the cooling front would move through a 30-foot deep
grain mass in a minimum of 15 hours and past a new layer of
sensors about every 1.5 hours (30 feet/15 hours = 2 feet/hour;
3 feet/2 feet/hour = 1.5 hours).
Thus, even though it may seem intuitive to place temperature
sensors more closely together along cables in shallower
depth bins, when the cooling front advances rapidly, a large
number of temperature sensors could be overkill as they will
not yield more useful information to the stored grain manager.
No explanation or supporting documentation is provided by
companies that manufacture and/or sell temperature cables as
to why one might select one or the other spacing of temperature
sensors along cables.
Spacing of temperature sensors
In terms of the number of cables and their placement in a grain
mass, a year-long aeration and storage period was simulated
using one of our computer models. The model used weather
and grain data to predict temperatures at more than 2,000 sensor
locations in the grain mass.
April 2022 / World Grain / World-Grain.com
http://www.World-Grain.com
World Grain - April 2022

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