Quote:
Originally posted by Cathar
I must admit that I'm slightly perplexed about people talking about using ultra-low flow rates through a TEC chiller.
It doesn't make sense to me.
TEC's are more efficient when their delta T between Tc and Th (cold and hot sides of the TEC) is low.
Now, as many waterblock tests have shown, block performance (measured as C/W) improves as the flow rate goes up.
This means that the dT within the TEC is lower, because the cold side is warmer, thereby raising its effiency. Even though it may seem somewhat counter-intuitive at first glance, the cold side being warmer is actually drawing more heat out of the water due to the increase in TEC efficiency.
When one wants to build a TEC based chiller, we want to follow exactly the same principles as for cooling the hot side of the TEC. We want the cold side to be kept warmer than with a less efficient block. TEC dT will therefore drop, the TEC efficiency will go up, and more watts of heat will be pumped from the cold side to the hot side. Now that wattage is coming out of the water, hence the water will get colder, faster.
Remember too, we're talking about closed loop systems, so it matter little what the entry/exit temperatures of the TEC chiller is. Over time, more watts are being drawn out of a fixed quantity of water than with a less efficient cold-side setup utilising ultra-low flow rates.
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A tec will be operating at X efficiency using the hot side cooling, insulation, voltage applied as adjustable variables. This is the tec itself, not the efficiency of the cooling chamber. The cooling chamber is actually the applied load to the tec cold side (heat stored in the cooling chamber block). Slowing the flowrate will increase the load seen by the tec.
Is this not the same thing you said quote "the cold side being warmer is actually drawing
more heat out of the water due to the increase in TEC efficiency.
" end quote
But the tec is not drawing heat out of the water, it is drawing it out of the heat stored in the coldplate. Slowing the flowrate increases the stored heat in the coldplate. In a die waterblock you want this stored heat to be minimal for a low die temp but in a chiller you want this stored heat to be high in the coldplate.
This is my logical understanding, please explain why I am off or on track.