Update 6:
Well being Christmas I haven't got a huge amount done but I have now go everything on order! YAY! So should be able to start putting parts together soon!
With that in mind I thought I would detail a few of the more unusual parts of the build:
Heat Exchanger:
To ensure heat exchange between the two sides of the TEC units I will be using two Lytron CP-15 cold plates. As per the picture below the cold plates will be mounted with the tubed copper in direct contact with the TEC units. Thermal resistance should be around 0.004 C/W at my expected flow rate, this (
if my calculations are correct!) at 24/7 power use of the TEC units should give a liquid temperature on the cold side of around -40 to -45 depending on ambient. Of course these are 'rough' calculations as there are far to many variables at play to get exact temperatures.
The cold plates are coming with pre-drilled M4 sized holes to allow the units to be bolted together at the required pressure. The TEC units will sit in a pre-cut 3mm thick silicon rubber gasket (
not sure if that's the correct terminology?!), to ensure separation of the hot and cold plates. The cold side of the plate will also be insulated by 6mm silicon rubber to ensure minimal heat loss.
I have chosen silicon rubber over closed cell neoprene as I am assured by the manufacture that it will retain its flexibility and rubber like properties down to around -80c, whereas the neoprene may not cope with constant -40c temperatures for long durations of time.
Cold Side Tubing Insulation:
The tubing on the cold side will need to be insulated to stop condensation and ensure minimum loss to heat to the sub-zero liquid. This will be achieved using nitrile rubber insulator tube which is rated for temperatures down to -50c.
The insulator tubing is relatively flexible and has a wall thickness of 13mm (
for a total tube diameter of 28mm) so shouldn't look to bulky.