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Before we can understand stacking you must first FULLY understand Qmax and dTmax
Qmax is the amount of heat that can be moved to a delta of 0 ( the hot and cold sides are = temps )dTmax is achieved when NO load is applied to the TEC and at this point Q =0 ( or the TEC can't move any heat load to a delta of 69 )As you apply a load to the cold side of the TEC the delta is reduced . that means if your cooling a cpu it is impossible to cool it to a delta of 69So you can't just add the dtmax's together and expect a delta of 138 NOW to stacking If you apply Umax ( full power ) to a TEC to get your Qmax and dTmax then ALL the electricity to do so is lost as heat to the hot side of the TEC . If your running the TEC's at full power then the TECs will use FAR more power than they can move. In the case of stacking the second set of TEC's has to move the previous set of TEC's "WASTE" heat as well as the load applied ( CPU ) this will mean that the total load applied to the second set of tec's will FAR exceed it's Qmax resulting in a fail IE ( im just making up numbers ) TEC can move 400 while used 600 of electricity CPU = 200 CPU =200 TEC 1 moves the 200 while adding 500watts TEC 2 then has to move the 200 watt CPU and the 500watts which equals 700 watts . However the TEC can only move 400 . so this can not work. Now you can get Stacking to work with having FAR more Qmax in the second level and or not running the TEC's at full power. however in both cases the Delta will be significantly reduced from a theoretical 69*2 |