Boiling R290 heat transfer coefficient

I am hoping to make a direct die system this summer, and was looking at the design of the evaporator. I have a besic design in mind, but was hoping to optimize the base thickness and fin design. I can do this relativly easily using ANSYS, but I would need to know the convection heat transfer coefficient for the R290 in the evaporator. I have looked at trying to figure this out through massive equations and the like, but things get so complex and have so many variables that the only realistic way to figure this out would be empirically.

Does anyone have any approximate values from their own systems or have any idea whay sort of h I should use?

i have about 2-3mm between the cpu and r290 refrigerant.
i know that the new chilly1 evaps have a thick base almost 10mm thick (i think dont quote me on that)
i think the thicker base migh hold better load temps?

a thicker base will mean ya have a higher and heavier block though.


what type of evap design you hope to use?

A thicker base will transmit more heat out to a larger surface area so it makes sence for high heat loads and very cold evap temps, but I don't think I'll be seeing either one of those. I was planning to make a block similar to the picuture below. The evap is made for a cpu sitting upright, like in a case. I would make it on a mill and have all the channels smooth, but I was actually thinking it would work better if I just did it on a drill press so the walls are all crazy and there is a lot more surface area. It's a bit of a pain to make it that way, but I think it's worth it.

One thing I'm not to sure about is how much of the refrigerent is in a liquid state. The design of the block below is essentially assuming that there is quite a bit of refrigerent in a liquid state, so the cup directly above the cpu is essentially filled with boiling refrigerent. If this isn't the case and the refrigerent is more like a vapour flowing through the block then a more conventional maze design would probably work better.

hope this helps a bit

http://www.airliquide.com/en/busine...19=34&RD24=62&RD25=77&RD26=78&RD28=81&RD29=82



sorry for the huge link

Thick base = better heat distribution, but also that's more range for temperature difference (like it's easier to have x*C difference on 10mm than on 2mm).

Problem that Icansee withthis picture is that if you won't use really thick base, only that U in centre will get heat from CPU, heat distribtuion to rest of block would be close to none. On the other hand - thick base isn't that great too...

I don't have expereince with phase change but if I could advice something, the best would be probably fins in star style - from centre to sides. This way they'd distribute heat inside themselves and wouldn't require that thick base. That's based on my water cooling experience, but I think that it should apply to this case too.
Closing stright fins copper heatsink in some can, with dual outlet at sides doesn't seem tobe bad in my consideration too.

What do you think about it?

I know what you mean about the tradeoff between high thickness to have more heat transfer area, or less thickness to have less thermal resistace. As far as I can tell the thickness is somewhat related to the heat load of the cpu. A very high heat load will need more thickness.

I am actualy planning on making the thickness increase towards the edge of the block, as there is no reason to have it thin there. I do like the idea of having some sort of solid fin going away from the centre though. Something to help move the heat outwards.

This is why I was looking for a rough value of H. With that I can make a computer model and use that to try and improve the design. I guess it isn't all that important though... it would probably only made a degree or two difference.

i think the way ya tweak the things more important. i have seen a lot of evaps.
they all seem to work much the same as others, darn cold.
i am gonna experiment with something similar to yours on a 30mm copper square for a gpu cooler. and then a 40mm one for the cpu.

i think the most important thing to take into account is how big its going to end up and the amound and quality of insulation you can apply and still be able to fit it to a cpu.

yea, my evaporator will have to fit on a soccet A with the 4 mounting holes right beside the soccet, so I am looking to make it pretty small. Hopefully I will be able to stick some extruded styrofoam right against the evap for insulation. It has about the highest R value for the thickness of anything I can think of.