Therefore, in Week 7 of the project, the cell was applied to the computer. Based on the computer architecture analysis completed in prior weeks, the optimum location to apply the cell was decided to be on top of the heat sink, which is on top of the processor. The heat sink of the laptop is not very efficient, and the surface of it reaches high temperatures when the computer processor is given a maximum workload. The surface reaches temperatures that could burn the skin if applied for several seconds, so it should provide enough heat for the cell.
The computer was loaded with large video files and a Maple 16 script with a continuous loop so that the computer processor and RAM could be given a maximum workload and therefore reach high temperatures.
The computer keyboard was removed, and part of a metal casing under the keyboard was cut so that the heat sink could be reached.
Computer
base with keyboard removed and area to cut marked in blue marker.
The
functioning computer with metal base cut for access to processor heat sink.
Now
that the computer was modified for access to its hottest heat source, the cell
could be applied. During Week 7, the
group completed the first application of the cell to the computer. The thermoelectric cell was applied to the
heat sink using Dynex thermal paste.
Dynex
thermal paste
The Dynex paste is comprised of silver and is believed to be
a better conductor of heat than air, and therefore these tests were predicted
to have better results than heat gun tests.
Then, in order to create a makeshift heat sink to keep the other side of
the cell cold to create the desired temperature gradient, a sheet of copper was
placed on the other side of the cell, with thermal paste.
For testing, the computer was turned on
and given a maximum workload, so that it reached a high temperature. The cell was then connected to the multimeter
to measure the generated voltage.
Week 7 Test Results:
Tests with thermal paste in the manner described above
resulted in generated voltages of only 0.1 to 0.2 volts.
Tests were also conducted without the use of thermal paste,
simply the cell on top of the heat source.
This resulted in voltages of 0.05 to 0.08 volts.
To the group’s surprise, the test
results were much poorer than expected.
The maximum voltage acquired was about 0.2 volts, and this is obviously
not enough potential difference to power the 5.0 Volt computer fan, or even a
1.5 Volt external LED light.
Initial cell testing on the computer
with thermal paste did not go as well as expected, however unexpected results
should be expected with all engineering projects of discovery.
The day after testing, the group searched for answers to
explain why the tests did not go well.
Several factors were deduced:
·
The application surface was uneven, and
the metals of the surface should be sanded down to create a flat, even surface.
·
The Dynex thermal paste was determined
to be inefficient. After learning about
its “Percent Metal Composition,” the amount of silver metal in the paste was
very low, and other thermal pastes are available with higher percent metal
compositions.
·
The temperature gradient between the
hot and cold sides of the cell was not good enough. A better heat sink is needed for the cold
side.
The group then found a better paste to use, Arctic Silver 5,
which was believed to have a percent metal composition at least one order of
magnitude higher than the Dynex paste.
This paste was purchased, as well as a silicone based heat sink
compound, for application of the heat sink.
Also mentioned above, a better heat sink was needed to
dissipate the heat from the cold side of a cell. Therefore, a heat sink was harvested from an
old desktop computer to be used on the cell.
Old
gateway desktop computer opened.
Aluminum
heat sink taken from desktop computer.
Next, the surface of the laptop were the cell was applied
was sanded down to create an even surface.
A piece of copper of the laptop’s heat sink was the problem, because it
rose above the metal around it.
Laptop
heat sink, cell application site, sanded down. View 1.
Laptop
heat sink, cell application site, sanded down. View 2.
Finally, more of the metal base under the keyboard was cut
so that the computer fan could be seen, and accessed if it is to be used in the
project.
Laptop
with heat sink and fan accessible.
The next step of the project will be
completed immediately at the start of Week 8.
The cell will be applied to the computer once again, however this time
with the improvements of:
- A
more even surface of application
- A
better thermal paste for a more direct and efficient transfer of heat
- A
real heat sink for an improved temperature gradient across the cell
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