[gone_fishin]

Originally posted by Cathar
gone_fishin, allow me to dissect your post if you will:



You also forgot to add that the efficiency depends on Th - Tc, being the temperature difference between the hot and cold sides of the TEC.

The greater the temp differental, the more the heat wants to flow back from the hot side to the cold side by natural forces of conduction as the TEC elements are essentially made out of metal.

You are right when you say that the TEC's efficiency is affected by hot-side cooling, but to say so is only stating half of the issue. The efficiency, being watts moved, is really affected by Th - Tc. The minimum temperature achievable by the cold side is a side-effect of keeping the hot side cooler. This is a desirable thing, but really what's going on is that we've lowered Th, and Th-Tc remains essentially the same (given perfect insulation and identical heat loads).



This one point hinges upon most of the others you made. The cold-plate is just a thermal buffer, in equilibrium the "stored heat" of it is essentially irrelevant. It does provide a thermal gradient though between the water/chamber and the TEC cold side.

Through increasing the water flow rate on the cold-side/cold-plate, we are increasing the TEC's cold-side temperature (because the water is always warmer than the TEC cold-side) due to an increase the thermal convectional transfer rate. In doing so, we raise Tc, and hence Th-Tc gets smaller, thereby improving the heat pumping efficiency of the TEC. Heat pumping, measured in watts, goes up, therefore there is an increased flow of heat energy moving from the water, to the cold side of the TEC (via whatever is sitting in between).

Now I can't be sure if this isn't exactly what you were already thinking or not. It could very well be, just that I disagree with some of the terminology used.

How can you say this stored heat is irrelevent? In simplistic terms it is the local heatload that the tec is seeing and moving. By saying it is moving the heat directly from the water is the same as moving further along the source path and saying the tec is removing the heat from the die. Also the heat being added by the die does not change, but the amount passing through the coldplate per unit of time can. The hotter coldplate would satisfy your argument of Th-Tc increasing heatpumping efficiency. Now how do you get a hotter coldplate? By lowering the flowrate.