Originally Posted by teatchme
Hi zipdogso, i appreciate your concern, indeed i have looked up cascade tecs and it's as u say: the dT is not much bigger and qmax is small. but i have been tossing some numbers around and efficiency seems pretty decent as well as cold side temp under a fully loaded cpu, 2 gpus.
i have a feeling the general limitation to cascade tecs is that way below zero dT exponentially struggles, and every extra C is very hard earned, so if i got it right untill i gow under 0C the dT does not take a serious hit. try running some numbers, cascade low V vs single high V. the efficiency is not that bad really.
There is another problem you will be better to put the 2 sets of TEC's side by side rather than one on top of another the hotside of the bottom set will be warming the coldside of the top set.
EDITED DUE TO AMBIGUITY :-
Your setup is WB - cascade TEC - WB - cascade TEC - WB
the middle WB is both cooled by the TOP set of TEC's and heated by the bottom set of TEC's.
Irrespective of what qmax the TEC's are because you are using cascades the heat from the bottom sets hotside will far exceed the cooling of the top sets coldside and you may well find the coolant in the middle WB actually gets quite a bit warmer NOT colder as planned.
If you need anymore convincing consider this :-
Lets say for instance the bottom TEC of each cascade has a Qmax of 50w, the max heat output of the hotside will be about 150w so the top TEC needs a qmax of at least 150w which will have a max heat output of about 400w.
So you have 4 of these cascades in the top row and 4 in the bottom row.
The max cooling power is = qmax of the bottom cascade TEC =50w times 4 cascades = 200w max cooling power.
the max heat coming off the hotsides of the bottom cascades = 4 times 400w = 1600w max heat coming of hotsides.
In the battle for domination of the middle WB who will win 200w cooling or 1600w heating...hmmmEdited by zipdogso - 7/14/09 at 7:20pm