EML3015C Thermal-Fluid I
Fall 1999
Lab. Assignment #2
Stefan-Boltzmann Radiation
Heat Transfer subjects reviewed: Thermal radiation, Stefan-Boltzmann law,
radiation emission
Description: Stefan-Boltzmann lamp is nothing more than an incandescent lamp with
a Tungsten filament as described in our lab. assignment 1, see the following picture.

The lamp can be used to provide high temperature radiation source for the
investigation of Stefan-Boltzmann Law.

If the surface temperature Ts is much higher than the surrounding
temperature Tsurr, the radiation heat flux is proportional to the surface
temperature to the fourth power.

In this experiment, we would like to investigate the validity of this relation by
measuring the radiation heat from the the heated tungsten filament at various
temperatures. The experimental setup is shown in the following figure.
Use the following procedures:
- Supply power to the lamp using the power supply (see picture). Vary the
power input into the lamp by adjusting the voltage setting. Observe that the
filament starts to glow, initially dark red to eventually incandescent white, at higher
voltage. Simultaneously record the voltage (V) and current (I) across the
filament. The filament resistance, R, can be determined as R=V/I
Power
Supply
- Determine filament temperature by measuring its electrical resistance. Like all
metals, the resistance of the tungsten filament is a function of its temperature, T.
Therefore, accurately determining the resistance is one of the best methods to determine
the temperature of the filament.
- Measure the reference resistance (Rref) of the filament at room
temperature.
- Use the following equation to determine the temperature of the filament:

- Measure the relative radiation heat flux using the radiation sensor as shown in the
following figures..

Sensor facing the room: low voltage reading

Sensor facing a hand: higher voltage reading due to thermal rdiation emitted from
hand
- Radiation sensor: A sensing element, consisting of a thin metal strip and a
thermopile, produces a voltage proportional to the temperature of the metal strip.
Through proper design, the temperature of the strip is also proportional to the intensity
of the radiation.

- At each voltage setting, record the voltage(V), current(I), and the voltage output
from the radiation sensor, Vsensor.
- Calculate R=V/I, and determine temperature T using the resistance-temperature
calibration equation.
- Construct a graph of Radiation heat flux (proportional to Vsensor)
versus T4. Does it represent a linear relation as predicted by the
Stefan-Boltzmann law?
- Construct a second graph of log(Vsensor) versus log(T). Determine
the slope of this linear relation. Discuss your results.