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Brians256 · 09-25-2003, 05:34 PM

My theory is based upon steady state situation, where the goal is to move as much heat energy as possible out of the water. The goal is not to get the lowest temperature water.

So, I assume that there is a there is a point of flow rate where higher flows or lower flows through the pelt block move less heat out of the water. I assume that this measurement is made with a controlled inlet temperature (i.e. higher flow tests weren't made with a larger pump that would dump heat into the system and vice versa) and all other system variables mostly controlled. Knowing BillA, that is what I would assume, since he has a good track record of trying to minimize independent variables.

1. As flow rate drops, T(water) decreases. This seems intuitively obvious.

2. Does the temperature on the hot side of the TEC go up, down or stay the same? Assuming that heat movement is INCREASING as flow rate decreases, the TEC hot side must increase. If more heat is being moved, the only place to dump it is the hot side of the TEC, and the only way to dump more heat is to move it across a steeper gradient. A higher temp on the hot side of the TEC allows more heat to be dumped (to air, water, etc...) at higher efficiences FOR THAT JUNCTION. A higher hot-side temp of the TEC allows more heat to be dumped from the TEC (temporarily ignoring where the heat comes from: CPU, TEC innefficiencies, etc...). To me, this is where the negative term on system efficiency arises. As flow rate increases, hot side temps drop and the TEC is working less to move less heat.

3. TEC efficiency decreases as dT increases. So, as flow rate decreases, the efficiency at which electricity is used to move BTUs/Calories decreases. Does this reach a limit of zero efficiency where the maximum dT for the particular device is reached when trying to cool a perfectly insulated cold side? Probably not relevant for our discussion, but I'm still curious. In any case, this trend introduces a positive coefficient in favor or higher flow rates.

It still seems wierd to me that the decreased flow would actually help, since it would *seem* that the decreasing efficiency of the WattsMoved/WattsElectricityConsumed term would dominate. But experimental evidence trumps all theory.

Is any of this making sense? If I'm not adding to the discussion, let me know and I'll shut up.

Just trying to learn.

09-25-2003, 05:34 PM	#100
Brians256 Pro/Staff Join Date: Oct 2001 Location: Klamath Falls, OR Posts: 1,439	My theory is based upon steady state situation, where the goal is to move as much heat energy as possible out of the water. The goal is not to get the lowest temperature water. So, I assume that there is a there is a point of flow rate where higher flows or lower flows through the pelt block move less heat out of the water. I assume that this measurement is made with a controlled inlet temperature (i.e. higher flow tests weren't made with a larger pump that would dump heat into the system and vice versa) and all other system variables mostly controlled. Knowing BillA, that is what I would assume, since he has a good track record of trying to minimize independent variables. 1. As flow rate drops, T(water) decreases. This seems intuitively obvious. 2. Does the temperature on the hot side of the TEC go up, down or stay the same? Assuming that heat movement is INCREASING as flow rate decreases, the TEC hot side must increase. If more heat is being moved, the only place to dump it is the hot side of the TEC, and the only way to dump more heat is to move it across a steeper gradient. A higher temp on the hot side of the TEC allows more heat to be dumped (to air, water, etc...) at higher efficiences FOR THAT JUNCTION. A higher hot-side temp of the TEC allows more heat to be dumped from the TEC (temporarily ignoring where the heat comes from: CPU, TEC innefficiencies, etc...). To me, this is where the negative term on system efficiency arises. As flow rate increases, hot side temps drop and the TEC is working less to move less heat. 3. TEC efficiency decreases as dT increases. So, as flow rate decreases, the efficiency at which electricity is used to move BTUs/Calories decreases. Does this reach a limit of zero efficiency where the maximum dT for the particular device is reached when trying to cool a perfectly insulated cold side? Probably not relevant for our discussion, but I'm still curious. In any case, this trend introduces a positive coefficient in favor or higher flow rates. It still seems wierd to me that the decreased flow would actually help, since it would seem that the decreasing efficiency of the WattsMoved/WattsElectricityConsumed term would dominate. But experimental evidence trumps all theory. Is any of this making sense? If I'm not adding to the discussion, let me know and I'll shut up. Just trying to learn.