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 Post subject: Building my own silent PC case
PostPosted: Mon Jun 26, 2017 7:30 pm 
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Joined: Sun Jun 18, 2017 8:02 am
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This will be a pretty long post, but I'd appreciate your patience in helping me build my first passively cooled PC case. I am aware that there's a new Calyos case that can passively cool even a 1080ti, and that it will outperform even the best DIY PC cases. Still, I'd like to build my own passive PC case so it stands out in the crowd while being very efficient.

Up until two weeks ago i've been thinking of buying a HD-Plex H5 case, but after reading up on heatpipes and looking at the H5 design carefully, I've realised that case is far, far from being the optimal passive cooling solution you can build. So there came an idea of building my own case.

My main goal is low temperatures and zero fans. I want the case to fix an ATX board, along with an SSD rack for at least 3-4 SSDs and an ATX power supply. The ATX board will be placed horizontally, while the GPU will also be horizontal with the use of a riser cable. It must passively cool a CPU and GPU of at least 95W each, with a potential of some overclocking as well. Maybe with potential of adding another GPU in the future. The size of the case I'll build does not matter, it can be as big as it needs to be, as long as it provides optimal cooling solution.

I've been reading up on heat pipes, vapor chambers and cool pipes for the past few days. I've browsed a few websites that offer large heatsinks, trying to figure out what will do the job the best for me. However I'm not afraid to admit that my thermodynamics knowledge is more than lacking. I have a few ideas of how my PC case should be made like, but most of those ideas are based on guesswork more than anything else.

I'll try to present the ideas I've thought of. I'd appreciate constructive criticism on my ideas and advice on how to make the case even more efficient at passive cooling. I'll be making a lot of comparisons to H5 case and how, to the best of my knowledge, it could be potentially improved upon.

I) How the HD-Plex H5 case works.

The H5 is using eight copper heat pipes for the CPU, as well as optional 8 for the GPU. Each heat pipe is 6mm wide and about 300mm long. The CPU makes contact with a ~600 gram, ~40mm high copper block. The bottom part is ~30mm high and square-shaped the same size as the IHS. The upper part is about ~10mm tall and has bigger surface to accomodate the 8 heat pipes (about 60mm x 60mm). It has indentations for the 8 heat pipes. After inserting the heat pipes, they protrude at about half of their height. To keep them in place, an aluminum heatsink is placed that also has similar indentations for the heat pipes. The heatsink is screwed together with the copper base. Thermal paste is used at each contact of metals.
The heat pipes are routed horizontally to the aluminum heatsink panel of the case, then bend 90 degrees to the right or left and make contact horizontally with the case via half-tube indentations similar to those on the copper base. Each of the two side panel heatsinks weight about 3kg and has eighteen 26mm long vertical fins. Each fin is about 5.5mm thick at its base and narrows along the way, reaching about 4.5mm at the end. Fins are spread about 12mm apart. Each fin runs vertically from the bottom to the top of the heatsink. The heatsink base is 9mm, and it has 3mm cuts for the heat pipes. So there's at least 6mm of aluminum through which the heat has to travel from the heat pipes to the fins.

II) Improvement ideas over the H5 design.

a) Using longer and wider heat pipes. According to this article, longer and wider heat pipes can transfer more heat. The biggest heat pipes I've found are 12mm wide and 600mm long. They are very expensive compared to what H5 uses, but it's a price I'm willing to pay if the performance will improve.

b) Running the heat pipes vertically instead of horizontally. According to the above article, it can greatly improve how fast the coolant can travel back to the area where it absorbs heat, therefore greatly improving heat transfer. It looks to be especially impressive for wider heat pipes, and has less effect on smaller ones.

c) With the above two points in mind, the heat sink panel must be taller to accomodate the longer heat pipes and the base of the heat sink must be thicker if I decide to use 12mm pipes; this brings an added benefit of more surface area on the fins.

d) More contact between heat pipes and the base of the heat sink. In H5 case, only about 50% of heat pipes' surface made contact with the heat sink base. I am unsure what's the best solution here. Should I find a workshop that can drill very precise holes of the same diameter as the heat pipe (or +0.1mm larger than the heat pipe)? Is this the best solution here? I've read of an "embedding" technique of the heat pipes, but I have no idea how that is executed and if any workshops would be willing to do that (and how difficult that process is). This would require the flattening of the heatpipes in the area of contact with the heatsink (which considering 600mm long pipes, would require to flatten about 75% of their length). Flattening the heat pipes reduces their cooling capabilities, so I'm unsure if I want to do that. I think the solution of drilling precise holes for the heat pipes to fit tightly would be the best?

e) Different thickness of the aluminum base of the heat sink. The H5 case's base is 9mm thick, but only 3mm are used for housing the heat pipes. So 6mm of aluminum base separates the heat pipe from the fins. To my general understanding, a thinner base would allow the heat to travel faster to the fins, which are responsible for dissipating the heat into the air. Am I wrong in thinking that? My idea is there to be only about 1mm of base thickness between the fins area and the heatpipe. This way the heat would get to the fins faster. Please correct me if my way of thinking is incorrect.

f) Make the base located between the CPU and heatpipes as thin as possible. Copper has several dozens times worse thermal conductivity than heat pipes. Therefore, the H5 design is not optimal, as the copper base is about 40mm tall. That's a lot of distance before the highly conductive heat pipes receive the heat from the CPU. I suspect they made that decision because some motherboards have oversized VRM heatsinks, so the wider part of the copper base had to be elevated in order not to conflict with other objects on the motherboard (?). I'd need to consider finding a motherboard that has a lot of room around the CPU area, in order to make the copper base as low to the ground as possible.

The idea is to make the heat from the CPU reach the heatpipes over as little distance of copper as possible. I'm not sure what would be the best way of doing the contact between copper base and heat pipes. I could do it like with H5 case (half-pipe shaped holes in both copper base and the upper piece that will rest above the heat pipes), or I could drill pipe-shaped holes in a one-piece copper base. I don't think flattening the CPU ends of the heatpipes will make much sense. One, this means I can fit less pipes across the limited width of the copper base. Two, flattening the pipes has an impact on cooling capabilities. So overall, I don't think trying to embed the heat pipes into the copper base is not a good idea.

I recently had a completely different idea of handling the copper base problem; instead of putting a copper base on the CPU, I could install a vapor chamber which can have flat dimensions of 50~60mm x 50~60mm. There should be enough space around the CPU for that. A vapor chamber has many benefits over a copper base. It has about 10-12 times better thermal conductivity than copper, and is capable of evenly spreading the heat over its surface. However, the vapor chamber is flat and thin. It's not possible to drill mounting holes for the heatpipes on the vapor chamber. So it will be necessary to flatten the ends of the heat pipes to a certain degree and place as many of them on the vapor chamber as possible. The more a heat pipe is flattened, the bigger negative impact on its performance. I'd need to consider the optimal flattening. Finally, secure the heat pipes in place with a top-mounted heatsink (aluminum with fins on top? or copper with fins on top? or copper with a flat top, so I could place a bigger heatsink on top of it?).

g) More vertical fins. The H5 case has less than 20 fins. Placing more fins will increase their surface area. However, I don't know what's the ideal spacing between the fins. Is there a point after which placing the fins more densely will bring no additional benefits, or even make the heat dissipation less efficient? Or should I just go with as many fins as I can find on the market?

h) Longer fins. The fins on H5 case are less than 30mm long. I found some heatsinks that offer fins up to 100mm long. What would be the best length? Is there a point where longer fins no longer bring any benefits, or even make heat dissipation worse? Or should I just go with the longest fins I can find on the market?

i) Thickness of the fins. In H5 case, the fins are 4.5-5.5mm thick. To my general understanding, thinner fins would make more sense because the heat can reach the air over shorter distance; this also allows for more fins to be packed across the radiator's length. Should I just go for thin fins?

j) Connecting the fins' ends with the base of the heat sink. The ends of the fins are usually very cold. If the base of the heat sink is only a little bit thicker than the heat pipes running though it, then the heat from the pipes has a short distance to travel before reaching the non-fin surface of the heat sink base. This creates the idea of connecting the flat base with the end of the fins through the sides of the heat sink. This could only potentially work well while connecting through the sides. Going through the bottom or top part would be a very bad idea. It would block the hot air from going up naturally, and it would block fresh air from entering between the fins from the bottom.

The connection between the base and the ends of the fins could be done with highly-conductive vapor chambers. However, the vapor chambers aren't infinite in length; the longest I could find were about 500mm long. This would mean I have to consider the fins length as well. It could be beneficial to make the fins (just an example) 20-40mm shorter to allow additional 20-40mm of vapor chamber to make contact with more fins.

You could place a lot of these vapor chambers next to each other, making it possible to transfer heat to a large portion of the fins' ends. However, won't it have a negative impact on airflow? This will cover the ends of the fins, which would mean the fresh air can enter only from below the fins and not along the side of the heat sink.

k) Place a heatsink with fins and very thin base inside the case as well. The additional heatsink would be screwed together with the outer heatsink on each wall that dissipates heat. This would require the case to have no top cover (not a big deal for me). This wouldn't interfere with PC components - the additional fins would be above all the components. The inner fins wouldn't pose a big barrier for passively cooling the motherboard components; there's still plenty of space between the fins so the warm air can rise from the motherboard.

l) (This one is probably incredibly stupid idea, but here goes anyway)
Routing one or two of the heatpipes through the fins. Is that a good idea? This would mean one or two heat pipes will run horizontally along the base of the heat sink (similar to H5 heat sink, run along half-pipe shaped incendations), make two 90 degree turns and then finally go through the fins.

==================================================================

Same considerations could be made for the second heat sink wall for the GPU. Third wall (front panel of the case) could be used for a 2nd GPU. The back wall would house the I/O part of the motherboard at the bottom. Not sure how I want to tackle the upper part of the back wall. I think the best idea would be to make it a giant heatsink with large fins as well, then connect the base of the back wall with the base of the walls responsible for cooling CPU and main GPU. This would allow the heat from the heat pipes travel to the back wall as well.

I'm not sure how high above the ground I want my case to be. Will it make any difference if I make the case 2cm above the ground, or 10+cm? Will more clearance between the case and the ground offer more air to enter the fin area? I'm also aware that the bottom plate on which the motherboard and other components will be screwed, needs holes for air to enter to cool the motherboard components.

The whole PC will be 100% fanless, including the PSU. I plan to buy some decent copper heatsinks for the mosfets as well as for the chipset. Are there any other components on the motherboard that would require better heatsinks in a no-fan case?

This became a very long post. Just noticed almost 3 hours have passed since I started writing it.

To summarize, I would like you to read through my ideas and comment on them. Are they good? Bad? Can they be improved even more? Is there anything else I forgot to mention? Anything else that can make the PC case more efficient at cooling?

TL;DR Please go read the whole post and help me with making my dream passive PC case :)


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 Post subject: Re: Building my own silent PC case
PostPosted: Fri Sep 01, 2017 12:37 pm 
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Joined: Sat May 06, 2017 7:40 pm
Posts: 8
Location: Los Angeles, CA, USA
Fascinating! But I have nothing to add, as I'm not engineering. Keep us posted.


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 Post subject: Re: Building my own silent PC case
PostPosted: Sun Sep 03, 2017 3:56 pm 
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Joined: Sat Oct 31, 2015 3:03 pm
Posts: 10
Ah, welcome to thermodynamics…

> making my dream passive PC case

If you’re serious about that, consider thinking way outside the box. (Pun not actually intended)

> The biggest heat pipes I've found are 12mm wide and 600mm long.

Look outside the PC industry, much longer heat pipes do exist.

“A pipe one inch in diameter and two feet long can transfer 12,500 BTU (3.7 kWh) per hour at 1,800 °F (980 °C) with only 18 °F (10 °C) drop from end to end”

https://en.wikipedia.org/wiki/Heat_pipe

Just make sure the working fluid boiling point is correct.

# # #

Basics of heat pipes indicate that as long as you have:

Adequate return of working fluid to the evaporator, and
Adequate elimination of heat from the condenser

you’re good to go.

A very outside the box solution, that should keep you cool no matter what the PC load is:

In a basically vertical position

Car radiator (~$75)
Heat Pipe
CPU

For best results, the condenser of the heat pipe should be in contact with the fluid in the radiator, so, yes, you’d need to drill a hole in the radiator. I’d also suggest offsetting the PC and adding a water barrier between the PC and radiator in case of leaks...

* As a side not, the old PC in a fish tank never really worked as it heat saturated the tank fluid as there wasn’t enough elimination of heat through the glass tank walls.

Consider also reading up on:

Solar thermal collector
Evacuated Tube Collector
Thermosyphons
Waste heat exchangers
Boiling point of liquids subject to vacume

> Still, I'd like to build my own passive PC case so it stands out in the crowd while being very efficient.

Go for it! Go wild even!

Best,
Michael


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 Post subject: Re: Building my own silent PC case
PostPosted: Thu Sep 07, 2017 2:13 am 
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Joined: Tue Nov 04, 2008 6:03 am
Posts: 447
Location: Sweden
Interesting topic! One of my first reflections is thet this will cost you a hefty bit of money...
My comments below are not based on hands on experience, but a deep theoretical knowledge in physics combined with things I've picked up over the years.

The H5 case is a prime example of how not to build a very efficient passive cooling. It's obviously designed primarily to fit the outer form factor and then get good enough cooling within that constraint.
What you should really use for inspiration is the (discontinued) Zalman TNN 500 case: A "chimney" design with vertical motherboard and graphics card to increase the convection air flow.

a) ... longer and wider heat pipes can transfer more heat.
Sure, over a longer distance. Wider pipes are also less efficient at picking up and deliver the heat. For your use it's better to have more thinner (6-8 mm) pipes than a few thick ones.

b) Running the heat pipes vertically instead of horizontally.
That's good.

c) With the above two points in mind, the heat sink panel must be taller to accomodate the longer heat pipes... and the base of the heat sink must be thicker ... this brings an added benefit of more surface area on the fins.
No matter what the heat sinks ("panel" plus fins as milled out of a solid slab of aluminum) need to be large, and tall is better than wide.
If with "base" you mean the cooling blocks mounted on CPU and GPU then it doesn't have to be very thick. "Direct pipe" is the way to go, and the block just needs to keep the pipes together and aid proper mounting.

d) More contact between heat pipes and the base of the heat sink. ... Should I find a workshop that can drill very precise holes of the same diameter as the heat pipe...? I've read of an "embedding" technique... This would require the flattening of the heatpipes in the area of contact with the heatsink... Flattening the heat pipes reduces their cooling capabilities, so I'm unsure if I want to do that.
You need good thermal contact between a sufficiently large surface area of the pipes and the heatsink slab.
* Drilling holes seems like the least simple way, given that good thermal contact can be difficult to ensure.
* Flattening the pipes (to a lesser degree, not totally flat) will improve the contact. Could be beneficial at the farthest end of the pipe where less heat is transfered.
* Half-round grooves in the slab allowing half of the pipe circumference making contact should be the primary option. Given that the length of each contact surface is 15 cm or more that should be more than plenty! (Add some TIM to the groove and use a beam or plate held with screws to press the pipes down.)

e) Different thickness of the aluminum base of the heat sink. ... 6mm of aluminum base separates the heat pipe from the fins. To my general understanding, a thinner base would allow the heat to travel faster to the fins, ... Am I wrong in thinking that?
A thin base is the best option for heat transfer from the pipe to the nearest fin, but you want to spread the heat over several fins. Experiments have shown that up to 7mm of thickness will improve the heat spread within the sink.

f) Make the base located between the CPU and heatpipes as thin as possible.
There should be nothing but an extremely thin layer of TIM between the CPU and the heat pipes! The base plate should be on top of the pipes.

g) More vertical fins. ... Placing more fins will increase their surface area. However, I don't know what's the ideal spacing between the fins. ...
h) Longer [more extended] fins. ... What would be the best length?
i) Thickness of the fins. ... Should I just go for thin fins?

These all depend on each other.
Tighter spacing => Less airflow. Generally for passive cooling I'd never go below 3mm on larger sinks.
Deeper fins => Less airflow. Need wider spacing to get cool air all the way in.
Thinner fins => Less heat spread within the fin.
With all this taken into consideration a good cross section could look much like a saw blade. The fins are thick with narrow spacing at the base to allow much heat to be transfered further out in the fin. Further out the fins are narrower and the gaps wider to allow for more air to pass by and pick up the heat.

j) Connecting the fins' ends with the base of the heat sink.
Not an issue when it's all made from a single piece of metal.

The connection between the base and the ends of the fins could be done with highly-conductive vapor chambers. ...
Vapour chambers are for use when space is at a premium. Not an issue here!

k) Place a heatsink with fins and very thin base inside the case as well.
No. The walls are the heatsinks, and the chimney effect will create proper cooling inside!

l) Routing one or two of the heatpipes through the fins. Is that a good idea?
From a cooling perspective it should have little to no impact if the rest is done right.
From an effort and cost perspective it's just a waste of resources.

I'm not sure how high above the ground I want my case to be. Will it make any difference if I make the case 2cm above the ground, or 10+cm? Will more clearance between the case and the ground offer more air to enter the fin area?
In theory high clearance is better, but there's also the effect of diminishing returns.
This case will be so heavy so I'd mount it on smaller furniture wheels that raise the bottom 4-5 cm off the floor. That's plenty enough for good cooling even if standing on a hairy rug.


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