Purpose
This experiment was intended for determining the thermal conductivity of aluminum metal.
Apparatus
The following materials were used in the experiment:
Variac
Timer
Digital thermometer
2 digital multimeters
Beakers
Tin can
Double throw switchers
Mercury thermometer
Heating plate
Wire
Ice cold water
Introduction
Heat flows from a hot region to a cooler region. However, the rate of heat flow varies from one medium to another. Heat travels through different media such as air, solid, and liquid. The mechanisms of heat transfer differ from one medium to another. For example, heat travels through a solid object by conduction while it travels through a vacuum by radiation.
Different solid materials have different capacity to conduct heat. This can be illustrated by holding two rods made of different materials (metals and wood) with one end of each being over the flame. In this case, the metal rod gets hot faster than the wooden one. Indeed, one cannot hold the metal rod for long unlike the wooden one. Different metals also have different capacity to conduct heat. This difference can be attributed to the difference in the properties of the metals such as the number of free electrons in each metal structure. Metals with many free electrons are more likely to conduct heat more than metals with few free electrons.
Thermal conductivity of a material shows its capacity to conduct heat. The coefficient of thermal conductivity is directly proportional to the thermal current. Materials with high thermal conductivity conduct heat faster than those with low thermal conductivity.
Procedure
Before starting the experiment, the students prepared by getting familiar with the equipment. In this case, the students ensured that they understood the connections and working of the multimeters. The wire and cable connections of the set-up were checked to ensure that they were connected properly.
Next, the apparatus was set up as shown in figure 1. Readings of V1, V2, V3, andV4 were then taken at room temperature using the double throw switches to ensure that all wires were properly connected. All wires read the same values, hence indicating that they were correctly connected. The variac was then set at 40 volts before the heating plate was turned on. Next, the tin of ice water was lowered onto the combination of metal cylinders. The readings of V1, V2, V3, andV4 were then taken every minute for 30 minutes. Lastly, the temperature of the heating plate was monitored using a digital thermometer to ensure that it does not go beyond 100ºC to prevent the melting of solder.
Figure 1: Setup for the Experiment
Results
The data for the experiment is shown is shown in table 1.
Data Analysis
The change in voltage at different point in time in the experiment is shown in the table below:
Thermal conductivity for Aluminum (K) at 30ºC
KAl=KCu*∆VCU∆VAl
KAl=385*0.00050.0003
KAl=962.5 W/mK
The thermal conductivity for aluminum as determined in the experiment is far much higher than the literature value. The literature value is 205W/mK (Orshansky, 75). This deviation could have been due to errors.
Works cited
Orshansky, Michael, Sani Nassif, and Duane S. Boning. Design for Manufacturability and Statistical Design: A Constructive Approach. New York: Springer, 2007. Internet resource.
