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Originally Posted by Fyber
Speaking of microchannels Cathar, how's that microchannel block coming along (Hydra I believe)?
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I've pretty much given up on micro-channels. The smallest channel block I had made up was 0.5mm. It performed well enough but really only roughly matched the 1mm channelled White Water as the impingement nozzle becomes largely ineffectual as the channels are reduced, and it's better/easier to just do the standard one-side-in to one-side-out style of channels once you get below about 0.8mm channel width.
The issue with smaller channels (truly micro-channels) that I could see was that as channel size is reduced further, meaning much below 0.5mm, the pressure drop required to push the water through those channels starts to climb fairly steeply, meaning that the pumps that hobbyists use today start to struggle to push even moderate amounts of flow.
My predictions were that somewhere around 0.2mm was the practical channel width limit for the pumps hobbyists typically use. It's possible to make 0.2mm channelled blocks in copper using photochemical resist etching. Given that we need to cool about a 20x20mm area to cover all types and orientations of CPUs, a 0.2mm wide set of channels with appropriately sized channel walls would present a total block restriction that would make the block barely able to achieve 1LPM flow rates even for higher-end pressure hobbyist pumps (MCP600, Mag3, Laing D4).
Now 1LPM, with water, is what I personally estimate the balance point is in terms of the point where the thermal capacity of the liquid flow through a block starts to become an increasingly dominant source of total thermal resistance within the block's operation regardless of how high
h, being the rate of thermal convection, is raised.
The other issue with making the channels smaller and then raising the pressure is pump heat. This is something that the EK pumps that Cooligy are looking at are an absolute necessity to solve. I do see a problem here though, Cooligy keep quoting 1W pump power consumption, but at some of the flow rates and estimated pressure drops that are being quoted, I see that 1W must be a lower end figure, and that to achieve some of what they're predicting to happen, pump power draw (according to the physics)
must be approaching 10W or more.
Cooligy's graph:
http://www.cooligy.com/images/microchannel2.gif
Is true, but only for a fixed flow rate. Once we start factoring in pressure drops, and perhaps more correctly plotting a 3-D surface of pressure-drop vs channel-width vs
h, we would see a surface that was hyperbolaic for
h as well as for pressure-drop. Plot a flat realistically achievable pressure-drop plane through the surface and the picture doesn't look so attractive any more.
Look, I'm not out to discredit Cooligy at all, but instead to critically analyse what they have presented so far. It does look like a decent form of waterblock technology, but I absolutely will not swallow the marketing material hook, line and sinker without first applying what I understand, have experimented, and can see, to the material as it is presented.