1. Results and Discussion
Effects of Radiation on Soil Temperature
Ramona Kahler, Alena Senf, Mallory Ware, and Dr. Drapcho
BE 4120 Heat and Mass Transport in Biosystems Engineering
Clemson University, Clemson, SC, 29631
References
1.Drapcho, C.(2019). BE 4120 Heat and Mass Transport- Lecture 16: Radiation.
2.http://precisionagricultu.re/soil-temperature-and-its-importance/
3.https://www.engineeringtoolbox.com/radiation-heat-emissivity-d_432.html
4.Drapcho, C.(2019). BE 4120 Heat and Mass Transport- Thermophysical Properties of Matter.
Acknowledgements
We would like to thank Dr. Caye Drapcho and the BE department for providing equipment and guidance.
Materials and Methods
Materials:
● Clay soil
● Grass
● Two 250 mL beakers
● Two Insulation bags
● Heat lamp
● Pyranometer
● HOBO software, datalogger and four temperature probes
In order to perform this experiment, two beakers were each
filled with approximately 200 mL of clay soil. One of the two
beakers were topped with approximately 40 mL of grass. Each
beaker was placed into an insulated bag under a heat lamp. A
pyranometer was placed at the same elevation as the beakers under
the lamp. Two HOBO data logger probes were placed into each
beaker, one at 24 mm and one at 65 mm. HOBO software was used
to collect the temperatures of each probe as well as the
pyranometer radiation readings every second for one hour under
the heat lamp.
Abstract
Soil serves as a major storage mechanism of heat, collecting
energy throughout the day and releasing heat to the surface during the
night. Over the course of a year, soil retains energy during warmer
seasons and releases heat to the air throughout colder seasons. Soil
temperature directly affects plant growth. Almost every crop slows
down its growth when soil temperatures are below 90℃ and above
50℃ (2). In order to determine the change in temperature at different
soil depths due to non-penetrating radiation, a bare soil sample and a
grass-covered sample were brought into the lab to test. A HOBO data
logger with temperature probes stationed at two different depths in
each sample was used. It was found that after 1 hour of light exposure
and an initial soil temperature of 22℃, heat is transferred faster in bare
soils as opposed to grass-covered soils. At the final time of 3760 sec:
Bare soil at 24 mm was 28.3℃, bare soil at 65 mm was 27.3℃, grass-
covered at 24 mm was 26.9℃, and grass-covered at 65 mm was
25.3℃.
Introduction
Solar radiation is described as the form of heat transfer that
occurs by electromagnetic waves from the sun to the earth. The radiant
flux from the sun, called irradiance (G), is measured in W/m^2, and is
approximately 1,370 W/m^2. After passing through earth’s
atmosphere, G is roughly 1,000 W/m^2, which differs in value
depending on latitude, time of year, and cloud cover. For a summer in
Clemson, the peak G value is between 800 and 900 W/m^2. For this
experiment, two soil samples were brought inside to test how a small
amount of radiation from a simple heat lamp can quickly increase soil
temperature at different depths, as well as with and without grass
cover.
Conclusion
The data collected showed that the grass acted as a buffer and reduced the temperature change at
similar depths of otherwise identical soils. The HOBO software shows that the radiation was relatively
constant, varying between 275.6 and 294.4 W/m^2. Furthermore, the data shows that the soil without the
grass both started changing temperature earlier and increased in temperature at a higher rate than the soil
with grass atop it. This is because the grass not only acts as a buffer layer, stopping the radiation from
initially transferring to the soil; it also increases the overall resistance value (R’).
Figure 5: The left beaker is filled with bare soil
and the right beaker is filled with grass-covered
soil.
Figure 1: The HOBO sensor screen
Figure 6: Each beaker was placed in an insulated bag while a
lamp was stationed above to heat the soil samples.
Figure 2: The HOBO data
logger measured
temperature change of
grass covered and bare
soils at two distinct depths.
Figure 3: A pyranometer
measured the irradiance
concurrently with
temperature data.
Figures 7 and 8: The temperature plots using COMSOL Multiphysics’ temperature modeling procedures at the end of data
collection. Temperatures closely resemble that of the measured values.
Figure 2 shows the change in temperature at different depths for both samples. As
expected, the bare soil samples showed higher temperatures than the grass insulated
samples. This graph also shows that the lower the depth, the lower the temperature.
Table 1 shows the analytical solutions to the temperature at time = 3760 s using the
equation shown in Figure 4. Since the heat lamp used was mainly comprised of
infrared radiation, the equation for non-penetrating radiation was used. The calculated
temperatures for the soil sample were quite close to the measured temperatures. Only
the first depth for the grass sample was calculated due to the presence of two layers.
The calculated temperature was much higher than the measured one. This is most
likely due to the fact that the temperature probe was partially embedded in soil as well
as grass.
Figure 3 shows the radiation measurements over time. Since the radiation was
from a heat lamp rather than solar radiation, the average radiation value was much
lower at 285.5 W/m2.
Table 1: Here are the calculated/ analytical values for heat flux (q”) and temperature at each depth.
Figure 4: The heat transfer analysis equation for non-penetrating radiation (1).
Table 2: Constants and
thermal properties used for
analytical calculations (3)(4).
