passive radiator design help needed

[metarinka]

hello, I'm in the process of designing a passive radiator. It would end up being about 88 feet of 3/4" thin schedule (M) copper pipe. I'm not sure if I really have a question just wanted to bounce it off you guys. My rather flaky math puts that at 2 gallons in the loop and I would probably have a half gallon res. I'm assuming just that much water in just about any decent container would be able to radiate enough heat for 1-2 computers.
The res itself would be more or less large concentric circles, with no tight bends, All joints brazed or tapered threads. The only issue I could think of is 3/4" pipe having to much constriction at 88 feet. My design will also allow me to double up and have 2 equal lengths of 45 ft pipe if flow is unacceptable. I'll be be using a large pond pump. off the top of my head in the 1300 GPH range.

any major things I'm over looking? will my pump asplode? I'll post some cad sketches as soon as I get my main comp back online. I'm a welding and fabrication major so the construction bit doesn't bother me and I have access to a full machine shop. Its the design and engineering aspect I must spend my time on.

[bigben2k]

Quantity of water is irrelevant; the heat resistance of the cooling solution is.

i.e. is this 3/4" tube finned? Are there any turbulators built inside? Fans or convection only?

Otherwise, I calculate the pressure drop as equivalent to 11 * 90 degree elbows: could be worse, but ought to be fine. Two PCs? I don't think so, unless the pump is hefty, and/or there are no other water blocks than CPU and/or the CPU water blocks are not too restrictive.

[bobo5195]

As a matter of fact passive cooling is what i'm having a look at now, its some hardcore stuff maths wise to calculate from first principals. Numbers may follow if i have time.

May i suggest this as a first punt guess, best thing that i could find in 2 minutes. http://www.coolingzone.com/Guest/New...t_CZ_2001.html

[BGP Spook]

bigben2k, wouldn't any bend in the pipe act as a slight turbulator? Owning to the tendency of liquids to 'stire' when they bump into eachother at relatively sharp bends

metarinka, I am haveing trouble envisioning exactly how you plan to run these concentric circles.

Are you going to winde it like a large spring? Or are you going to have a verticle pipe with two groups of half circles running to another verticle pipe.
Or am I WAY off?(Likely, very likely.)

[bigben2k]

There is a bit or turbulence, but not significant enough to have an impact here (I'm assuming a 6" to 12" diameter coil type of assembly, or more).

Search these forums for the turbulators that Hayden puts into its products.

[BillA]

use a low heat generating pump
the DDC is fine, velocity is not needed

[Brians256]

Has anyone taken a cast-iron radiator (for rooms) and used it? Sounds heavy but might be cheaper and better than DIY copper runs especially if the computer is not always on.

[Etacovda]

you'd need a nice anti-corrosive mix for that, id imagine

[TerraMex]

Brians: why? you can use a radiator from a car motor (not a heatercore) for that matter, bolt it to the lateral of the case -> done.

different approach,
i've posted this before, can't seem to find where, so here they are again :

not mine.

[metarinka]

okay a little more. The inside globe has a 2' diamater and the copper tubing has 2" spacing from the globe, and 3" spacing from itself. The smallest circle has about a 11" diameter, and the 180 deg U's span the ~4" gap (they will be formed by hand on a mandrel not 90 deg L's) I sketched it very fast so the 180 deg U's will be spaced further apart. there will be at least 4 brass unions so that the rigid radiator can disconnect from the inner globe, and so that it can disconnect in half to be seperate (none of that is shown)

the pipe will remain as is, no fins or extra turbulence, I'm figuring its only advantage is it's extrodinary length with hopefully low constrictions.

the res will be mounted at the bottom of the loop and there will be ball joints so that when disconnected the rad nor res would flow out (if desired). it would have 2-4 extra threaded holes to mount a second pump which will pump the loop for the extra comp and a set of spares to possibly include a 2nd computer.

is it making a little more sense now? The radiator loop will operate seperately of the computer loop and have its own pump, I'm guessing a high flow pond pump (22gpm at no head) with no constrictutions (besides unions) could operate around 10+ GPM but i could be way off, I'm on the fabrication side, not the engineering.
I'll polish and post the sketch if anything else needs clarification.

did I miss anything obvious

[TerraMex]

still think is too much hassle -> better options available, less heavy ones too (88 feet? eesh)



unavailable for comment.
j/k

[BGP Spook]

I am speechless.

[Etacovda]

metarinka is a poster over at bit-tech (or was?) so i assume this is for a modding project.

Id avoid the high flow pumps meta, they consume a lot of power, which in turn is dumped into the water. You should reduce the amount of wattage applied as much as possible in a passive set up.

[BillA]

use that baseboard heating tubing with the fins normal to the tube

but pyramids have special power eh ? HEY, quartz crystals too !

[metarinka]

etacovda yes I am over at bit-tech (I don't recognize your name) and indeed this is for a modding project, I'm a welding and fabrication major and I'm working on my junior year project. I'm trying to get away from building simple square frame cases and do some creative pipe bending (hey we have a hydro former and cnc pipe bender). It's clearly for looks, I'm just hoping its functional enough. Both pumps would be ran inline and the pond pump could be throttled back. Another thing is If I mount the pump at the bottom would I have to worry about the head? only roughly half the distance would be vertical, would that effect flow much?
Off the top of my head 88 feet of thin schedule pipe would be <35 lbs but I can't remember I mostly work with L schedule pipe. I don't think this would be a heavy case to work with (just big)

The interior will probably be a rather standard TIG welded extruded almuminum box frame the globe would be 2 acrylic domes.

[BGP Spook]

Originally Posted by BillA

but pyramids have special power eh ? HEY, quartz crystals too !

I think that is an Indiana Jones joke of some sort.....(unless I am WAY off on what I think that pic is)

Edit: sorry for thread hijack

[metarinka]

Originally Posted by BGP Spook

I am speechless.

I hope thats in a good way

at any rate this is still just some design notes, several sketches and a page full of price lists and parts. I'm going to make complete custom case this semester and If this design is unfeasible I'm going to a submersion design (why can't I pick the easy stuff)

[BGP Spook]

It was. I have it in my mind to try some hard to do stuff but that kind of tops anything I have considered.

[TerraMex]

I think that is an Indiana Jones joke of some sort.....(unless I am WAY off on what I think that pic is)

not off, indy there escaping the boulder.


--------

anyway, i'd be more concerned about the weight of that thing,
88 feet of copper tubing, plus water, -> not lan friendly for sure .

btw, from a pro-user (i'm too lazy to search for the thread) :

[BillA]

baseboard heating tubing, nice for passive if fins are vertical

[Etacovda]

i dont post much, meta - i read fairly often though

[ProHandyman]

I like BillA's suggestion. Fin tube can be had in 1/2 and 3/4" cores, with many lengths available. Fastened fin can be removed for custom sizes and swedging for joining. Many possible shapes could be configured from an asthetic view point. Fin tube would also help in heat transfer. Use residential instead of commercial... parts are lighter weight.

[metarinka]

been looking into finned tubing, I haven't done a price request yet (afraid to ask).

The big issue might be bending as some of the types of finned tubing can't be bent at all, I believe helicoil can and there are some resistance welded carbon steel tubes that can, but I would prefer to stick to plain copper, or even aluminum.

on another note, I'm really dumb. Did the math again and I came out at 52 ft of tubing. Not sure where I got an extra 30 ft.

[metarinka]

heres a copper pipe reference and current price list. 50 ft is only 15-20 pounds.

http://www.muellerindustries.com/wudfs/curacrt.pdf

[metarinka]

just bought the copper today, 60 foot coil of 3/4 NPS = 7/8 od and almost 3/4 I.D.
I also bought the acrylic domes from canada. Now I'm just gonna scrounge some old mild steel for a frame and look for a pump to push those beefy pipes (55 feet of this pipe will be 1.25 gallons in the loop and weight 40 pounds with the water)

I wanted to get the thinner copper ACR tube in a true 3/4 size but its hard to find fittings for that, and its hard to find it period. I got a reaally nice price on this stuff.

If anyone is interested I'll keep you guys updated