4 ms·

> TPU chips are hooked up in series in the loop, which naturally means some chips will get hotter liquid that has already passed other chips in the loop. Coolin

> TPU chips are hooked up in series in the loop, which naturally means some chips will get hotter liquid that has already passed other chips in the loop. Cooling capacity is budgeted based on the requirements of the last chip in each loop. Of course, it's worth noting that if you've got four chips, each putting out 250W of power, and a pump pushing 1 litres of water per minute through them, water at the outlet must be 14°C hotter than water at the inlet, because of the specific heat capacity of water. That's true whether the water flows through the chips in series, or in parallel.

foota 1y ago
Hm... but in the case when the chips are in serial, the heat transfer from the last chip will be less than when the chips are in parallel, because the rate of heating is proportional to the difference in temperature, and the water starts at a lower temperature for the parallel case for this last theoretical chip.
- fraserphysics 1y ago
  One way to characterize the cost of cooling is entropy production. As you say, cooling is proportional to difference in temperature. However, entropy production is also proportional to temperature difference. It's not my field, but it looks like an interesting challenge to optimize competing objectives.
- 0x457 1y ago
  Yes, but water is constantly moving in a loop. It's not like you use water to cool chip #1, and then it moves to chip #2, it's constantly moving, so temperature delta isn't that much.
  - smachiz 1y ago
    in their first serial design, that's exactly what it was doing.
    - Dylan16807 1y ago
      They mean it doesn't sit around and wait until it's hot, which then makes it "used" and unable to cool something else. It keeps moving through the first chip and is only a small percent saturated.
      - smachiz 1y ago
        depends how fasts it is moving - but it's all moving at the same speed. The last chip will get less cooling than the first chip, proportional to the amount of cooling the previous chips received. Delta T doesn't lie. Whether it's significant or not, I can't know - but you want it to be significant, otherwise it's less efficient.
        Dylan16807 1y ago
        > depends how fasts it is moving - but it's all moving at the same speed. The last chip will get less cooling than the first chip, proportional to the amount of cooling the previous chips received. Delta T doesn't lie. The watts of cooling per chip will be the same. The last chip in the loop will be a little warmer, but not by much in a reasonable setup. The difference in temperature between each chip and the water running across it will be the same. And if you take a weak water supply and then split it to run in parallel, you can end up with a significant heat gradient across each waterblock which doesn't sound great either. If you have 4 high power chips please don't limit them to .25 liters per minute each. > Whether it's significant or not, I can't know - but you want it to be significant, otherwise it's less efficient. Keeping your fluid cool is good for long term reliability. And if you're doing that, then every block is getting cool fluid and the other details about loop layout won't matter.
        0x457 1y ago
        It moves fast enough that the temperature delta between first and last chip isn't significant. Not too fast, though, because if the pump is running full-tilt it becomes a major heat-source itself. > but you want it to be significant, otherwise it's less efficient. No? You want a large delta between heat-source and water, as well as water and whatever is on your cool side. Essentially just between hot and cold sides. Delta between heat-sources is irrelevant unless you start cherry-picking some very odd combinations.
- chickenbig 1y ago
  In steady state the power put into the chip is removed by the water (neglecting heat transfer away from the cooling system). The increased water temperature on entering into the cooling block is offset by a correspondingly higher chip temperature.
idiotsecant 1y ago
It just means in series that some of your chips get overcooled in order to achieve the required cooling on the hottest chip. You need to run more water for the same effect.
- k7sune 1y ago
  I can imagine a setup where multiple series of slower cooler water converging into a faster warmer stream, and the water will extract an equal amount of heat away from all the chips whether upstream or downstream.
friendzis 1y ago
While there is some truth to your comment, it has no practical engineering relevance. Since energy transfer rate is proportional to temp difference, therefore you compute the flow rate required, which is going to be different if the chips are in series or in parallel.
- Dylan16807 1y ago
  If you're heating up the water by 10 or so degrees on typical computer hardware, I bet you're not bottlenecked by energy transfer. Your flow rate is based on how hot you want the water to get, so series or parallel goes back to not mattering.
JonChesterfield 1y ago
The equations all work out OK though since one can go substantially above a litre a minute at pressures which are still viable. The standard 18W thing for desktops is about ten times that.

foota 1y ago

Hm... but in the case when the chips are in serial, the heat transfer from the last chip will be less than when the chips are in parallel, because the rate of heating is proportional to the difference in temperature, and the water starts at a lower temperature for the parallel case for this last theoretical chip.

fraserphysics 1y ago
One way to characterize the cost of cooling is entropy production. As you say, cooling is proportional to difference in temperature. However, entropy production is also proportional to temperature difference. It's not my field, but it looks like an interesting challenge to optimize competing objectives.
0x457 1y ago
Yes, but water is constantly moving in a loop. It's not like you use water to cool chip #1, and then it moves to chip #2, it's constantly moving, so temperature delta isn't that much.
- smachiz 1y ago
  in their first serial design, that's exactly what it was doing.
  - Dylan16807 1y ago
    They mean it doesn't sit around and wait until it's hot, which then makes it "used" and unable to cool something else. It keeps moving through the first chip and is only a small percent saturated.
    - smachiz 1y ago
      depends how fasts it is moving - but it's all moving at the same speed. The last chip will get less cooling than the first chip, proportional to the amount of cooling the previous chips received. Delta T doesn't lie. Whether it's significant or not, I can't know - but you want it to be significant, otherwise it's less efficient.
      - Dylan16807 1y ago
        > depends how fasts it is moving - but it's all moving at the same speed. The last chip will get less cooling than the first chip, proportional to the amount of cooling the previous chips received. Delta T doesn't lie. The watts of cooling per chip will be the same. The last chip in the loop will be a little warmer, but not by much in a reasonable setup. The difference in temperature between each chip and the water running across it will be the same. And if you take a weak water supply and then split it to run in parallel, you can end up with a significant heat gradient across each waterblock which doesn't sound great either. If you have 4 high power chips please don't limit them to .25 liters per minute each. > Whether it's significant or not, I can't know - but you want it to be significant, otherwise it's less efficient. Keeping your fluid cool is good for long term reliability. And if you're doing that, then every block is getting cool fluid and the other details about loop layout won't matter.
      - 0x457 1y ago
        It moves fast enough that the temperature delta between first and last chip isn't significant. Not too fast, though, because if the pump is running full-tilt it becomes a major heat-source itself. > but you want it to be significant, otherwise it's less efficient. No? You want a large delta between heat-source and water, as well as water and whatever is on your cool side. Essentially just between hot and cold sides. Delta between heat-sources is irrelevant unless you start cherry-picking some very odd combinations.
chickenbig 1y ago
In steady state the power put into the chip is removed by the water (neglecting heat transfer away from the cooling system). The increased water temperature on entering into the cooling block is offset by a correspondingly higher chip temperature.

idiotsecant 1y ago

It just means in series that some of your chips get overcooled in order to achieve the required cooling on the hottest chip. You need to run more water for the same effect.

k7sune 1y ago
I can imagine a setup where multiple series of slower cooler water converging into a faster warmer stream, and the water will extract an equal amount of heat away from all the chips whether upstream or downstream.

friendzis 1y ago

While there is some truth to your comment, it has no practical engineering relevance. Since energy transfer rate is proportional to temp difference, therefore you compute the flow rate required, which is going to be different if the chips are in series or in parallel.

Dylan16807 1y ago
If you're heating up the water by 10 or so degrees on typical computer hardware, I bet you're not bottlenecked by energy transfer. Your flow rate is based on how hot you want the water to get, so series or parallel goes back to not mattering.

JonChesterfield 1y ago

The equations all work out OK though since one can go substantially above a litre a minute at pressures which are still viable. The standard 18W thing for desktops is about ten times that.