School of Design and Engineering
A laboratory report on
Thermal Radiation
Course:
MENGR 428 Thermodynamics and Heat Transfer II
Students:
Fahad Alwubayran
Mitchell Spall
Spring 2019
1. Introduction
The objective of this laboratory is to dive into the basic properties of thermal radiation. In
this simple experiment, the aim is to examine the emissive power of energy radiated by a body as
a function of its temperature. This is done by investigating the emissivity of different surfaces in
Leslie’s cube. This instrument consists of a cube with surfaces coated in different materials. The
group hypothesizes that each surface has different emissivity. To verify this hypothesis, the
following experiment is conducted.
2. Experiment and Measurements
To perform the experiment, the following instruments are needed. The first instrument is
Leslie’s cube which is TD-8554A Radiation Cube by PASCO scientific. This instrument is
heated by 100 W light bulb and inside the cube. Meanwhile, the surfaces of the cubes will
generate thermal radiation to the surroundings. The other instrument is the PASCO TD-8553
Radiation Sensor. It allows us to measure the radiation emitted from each surface of the cube by
producing a voltage that is proportional to the radiation quantity [1].
To reproduce the experiment, result the following steps must be followed. First, the
Ohmmeter and Millivoltmeter must be connected to the Radiation Cube and the Radiation sensor
as in Figure 1. Second, the power switch of thermal Radiation Cube is turned on to “HIGH”,
while monitoring the ohmmeter reading. Third, as soon as the ohmmeter reading is approaching
20K Ω, the power knob is turned to down to 5. Fourth, waiting for equilibrium to be reached, the
ohmmeter reading fluctuates until it reaches a fixed value. Fifth, the Radiation Sensor is used to
measure the radiation emitted from each of the four surfaces of the cube. This is done by putting
the sensor props in contact with the surface of the cube from which the radiation is measured.
Sixth, the resistance reading is taken from the ohmmeter to the following table. Seventh, the
previous step is repeated three times and the average resistance is taken for higher precision.
3. Results and Discussion
To find the emissivity and energy radiation rate of the different surfaces, Stefan Boltzmann Law
is used. It is also known that E(dot) = Eε where E is the electrical power, and ε is the emissivity.
Assuming that the fully black surface is an emissivity equal to 1, the sensor reading of the black
surface is divided by each of the other sensor readings. The following table provides the data and
calculation results. After finding the emissivity for all surfaces. The Energy radiated through
each surface can be calculated using Ε(dot) = εσΑΤ^4, where the area of each surface and the
temperature are known.
Surface
Sensor Reading (mV)
Emissivity (ε)
Black
10.6, 10.6, 10.6 (avg. 10.6)
1
White
10.3, 10.4, 10.4 (avg 10.367)
0.978
Polished Aluminum
0, 0, 0, (avg 0)
0
Dull Aluminum
2.9, 2.8, 2.7 (avg 2.8)
0.264
4. Conclusion
In conclusion, the experiments introduce the concept of thermal radiation by establishing the
concept of emissivity. Through this experiment, it is proven that different materials have
different thermal ratios. Consequently, the rates of heat transfer through radiation differs. It is
also noted that polished aluminum had the worst thermal radiation due to lack of emissivity.
Meanwhile, the white face provided the best heat transfer rate due to relatively higher emissivity.
This lab provided further knowledge of thermal radiation.