What factors influence the performance of a phase change evaporator block?

redleader · 02-03-2004, 08:02 PM

Obviously we all know how to approximately judge the various designs of a waterblocks. However I don't really know what makes a good evaporator in a phase change system. At first I thought it would be similar to a waterblock. However since a the compressor obviously has incrediable pressure developed, I don't think this is the case.

Most designs I've seen have actually been maze's very similar to my Maze2 Classic. Has anyone ever tried nozzels? How important is raw surface area?

I'm not even sure what makes a good block.

killernoodle · 02-03-2004, 09:08 PM

Fairly important when implementing a jet nozzle.

SA, the thinness of the base, and the speed of the flowing water wre all important to the cooling capacity of the waterblock.

satanicoo · 02-03-2004, 10:20 PM

Wondering about this for a good time myself.
With a pressure developed by a compressor, i thought the design of a very restricted WW would be good for this.

But i dont know the thermal capacity of the gazes used on phase-changing, if its way lower then water, maybe then it should be recalibrated to it (lower tickness fins?).

killernoodle · 02-03-2004, 11:27 PM

You cant use a thin base, you must use 100% soldered copper, and the internal SA still has to be high. Also, in order for there to be a serious temp drop, the volume of the waterblock has to be quite high because there must be a gigantic pressure drop from the capillary tube to the evaporator.

redleader · 02-03-2004, 11:36 PM

Quote:

Originally Posted by satanicoo

Wondering about this for a good time myself.
With a pressure developed by a compressor, i thought the design of a very restricted WW would be good for this.

But i dont know the thermal capacity of the gazes used on phase-changing, if its way lower then water, maybe then it should be recalibrated to it (lower tickness fins?).

Assuming they're phase changing, it the gas should be between 3 and 4 orders of magnitude higher then the heat capacity of water. The part i don't understand is how do you maximize the phase change.

8-Ball · 02-04-2004, 06:35 AM

I have been looking through the xtremesystems.org forums into the designs of evaporators.

The fact that a phase change is taking place makes it a lot more difficult to produce an evaporator which functions well. A few key points.

You need to think about the orientation of the block. Remember that there will be a mixture of liquid and vapour in the block. Ideally, you don't want liquid refrigerant returning to the compressor, but equally, you DO want some way of ensuring that the oil mixed in with the coolant DOES get back to the compressor.

Narrow channels promote a high velocity of refrigerant which can drive the oil back to the compressor and is a good solution, provided you can guarantee that all of the refrigerant vapourises.

To be honest, I don't really know enough about the subject to be able to help, though I would suggest looking at the aforementioned forums. There are a lot of knowledgable guys there working with some pretty remarkable phase change setups. (Think -100degC in a dual compressor cascade system!!!)

8-ball

redleader · 02-04-2004, 02:38 PM

Thanks 8-Ball. I noticed your post the other day on xtremesystems.org. Good to see someone setting people straight about metals and conductivity.

I'll look through their forum for more ideas. Right now though I'm leaning towards using a converted Maze Classic:

http://www.dangerden.com/images/MAZE2/MAZE2_large.gif

Its got surface area, narrow channels, and I already have one so its free

Hopefully oil won't be too big a problem.

02-03-2004, 08:02 PM	#1
redleader Thermophile Join Date: Jun 2001 Location: The deserts of Tucson, Az Posts: 1,264	What factors influence the performance of a phase change evaporator block? Obviously we all know how to approximately judge the various designs of a waterblocks. However I don't really know what makes a good evaporator in a phase change system. At first I thought it would be similar to a waterblock. However since a the compressor obviously has incrediable pressure developed, I don't think this is the case. Most designs I've seen have actually been maze's very similar to my Maze2 Classic. Has anyone ever tried nozzels? How important is raw surface area? I'm not even sure what makes a good block.

02-03-2004, 09:08 PM	#2
killernoodle Thermophile Join Date: Sep 2002 Location: Charlotte, NC Posts: 1,014	Fairly important when implementing a jet nozzle. SA, the thinness of the base, and the speed of the flowing water wre all important to the cooling capacity of the waterblock. __________________ I have a nice computer.

02-03-2004, 10:20 PM	#3
satanicoo Cooling Savant Join Date: Nov 2002 Location: portugal Posts: 635	Wondering about this for a good time myself. With a pressure developed by a compressor, i thought the design of a very restricted WW would be good for this. But i dont know the thermal capacity of the gazes used on phase-changing, if its way lower then water, maybe then it should be recalibrated to it (lower tickness fins?). __________________ back.

02-03-2004, 11:27 PM	#4
killernoodle Thermophile Join Date: Sep 2002 Location: Charlotte, NC Posts: 1,014	You cant use a thin base, you must use 100% soldered copper, and the internal SA still has to be high. Also, in order for there to be a serious temp drop, the volume of the waterblock has to be quite high because there must be a gigantic pressure drop from the capillary tube to the evaporator. __________________ I have a nice computer.

02-04-2004, 06:35 AM	#6
8-Ball Cooling Savant Join Date: Feb 2002 Location: Oxford University, UK Posts: 452	I have been looking through the xtremesystems.org forums into the designs of evaporators. The fact that a phase change is taking place makes it a lot more difficult to produce an evaporator which functions well. A few key points. You need to think about the orientation of the block. Remember that there will be a mixture of liquid and vapour in the block. Ideally, you don't want liquid refrigerant returning to the compressor, but equally, you DO want some way of ensuring that the oil mixed in with the coolant DOES get back to the compressor. Narrow channels promote a high velocity of refrigerant which can drive the oil back to the compressor and is a good solution, provided you can guarantee that all of the refrigerant vapourises. To be honest, I don't really know enough about the subject to be able to help, though I would suggest looking at the aforementioned forums. There are a lot of knowledgable guys there working with some pretty remarkable phase change setups. (Think -100degC in a dual compressor cascade system!!!) 8-ball __________________ For those who believe that water needs to travel slowly through the radiator for optimum performance, read the following thread. READ ALL OF THIS!!!!

02-04-2004, 02:38 PM	#7
redleader Thermophile Join Date: Jun 2001 Location: The deserts of Tucson, Az Posts: 1,264	Thanks 8-Ball. I noticed your post the other day on xtremesystems.org. Good to see someone setting people straight about metals and conductivity. I'll look through their forum for more ideas. Right now though I'm leaning towards using a converted Maze Classic: http://www.dangerden.com/images/MAZE2/MAZE2_large.gif Its got surface area, narrow channels, and I already have one so its free Hopefully oil won't be too big a problem.

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