Be warned about information you get off the internet about
thermocouples. One popular site says a thermocouple is "...a junction of
dissimilar metals that creates a voltage you can relate to temperature." This
misinformation continues to appear on company web sites, in application notes,
and in articles. You could make a simple thermocouple from copper and iron wire
(see diagram below) using boiling water and icy water to calibrate your device.
Then you could investigate the cooling curve (and time constant) when the hot
end is allowed to cool in a gentle breeze. Or you could look at ways of forming
the junction (twisting, soldering, welding). Or how about different alloys and
what factors influence the voltage (resistivity perhaps). There are lots of
things that would make a great EEI.