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There is an optimal ratio of internal heat sink to external radiator. My heat sink inside is too small to be effective it can only cool the air that passes over it and in this case that is not enough to be effective and efficient. Therefore no matter what voltage I apply and how cold the chilled TEC surface gets the sink cannot collect enough BTUs to really make the big external radiator system work.
For air chilling the internal HS needs to be pretty big actually, more surface contact with the airflow, more BTU's sucked up to be moved away.
I've just built an external base chiller using 50 x 50 Alum Angle and insulated it with Styrofoam. The Angle goes up the back of the 450D with a wee gap and is a sealed cavity and the base is also insulated plus I've used silica heat grease to even get some transfer through the plastic bottom surface. I even extended the foam up the left side and sealed any gaps to minimise any air exposed chilled surfaces.
It works but it is slow and it only got 4* cooler than ambient after nearly 60 mins of 12volts. There was dew dripping off the rear exposed alum plate and the plate was very cold. It is just that the minimal contact are only allows minimal heat transfer. The big radiator on the back was barely warmed, not enough coming through to make it work.
A hermetically sealed, well insulated enclosure with a big internal heat sink and fan as per Gary Honiss's build seems the best option.
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