Project: Hush! - updated 26/12/23

[Monkey Puzzle]

Project: Hush!

Taster pics:

Update Links:

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Hello all. I've started making a large passive radiator/case. I've been working on it for a while, but since the design is quite complicated I thought I'd wait until it got to a recognisable, likely to work(!) stage before starting the build log.

I have had an innovatek Konvekt-o-matik before selling it on members' market, but from what I've heard you really need a shedload of them to handle high heatloads. Plus, they're expensive (~£80/6tubes), bulky and the design is flawed in my opinion - aluminium, made for 8mm ID tubing, and by their design the more of them you add the larger the pressure loss - 8mm inlet splits to 8mm tubes running in parallel.

So I figured I'd make my own;

copper,
designed for 7/16" or 1/2" tubing,
minimise pressure loss by matching resistance of the tubes to 1/2" tubing,
massive amount of surface area (since it's the equivalent of an Aga it needs to have headway for extra heatload),
wide fin spacing and compact enough to be self-contained within a case.

The case is going to be approximately 45cm wide x 40cm deep x 46cm tall + height of castors. So it's slightly smaller than a mountain mods UFO (45x45x45)

The top, far side of the case (the non-window side panel on a normal case) and the bottom will be made up of a large finned copper radiator, hopefully with enough surface area and passive airflow to run completely passive, with air rising up through the case. I wish I was competent enough with google sketchup to draw a detailed plan, but it just seems a nightmare because of the design, so I'm afraid I've largely stuck to hand-drawn sketches. Here's a very rough idea of what the passive radiator element of the case will look like.

Initially I was going to use 30 metres of standard 15mm outer diameter half-hard pipe used in home plumbing and flatten it as in normal watercooling radiators, but after buying a small sample (a gentle elbow bend) and trying to flatten it I realised it's very tricky to get an even inner channel, and it would take forever to flatten 30m of the half-hard stuff...

After scouring around to find a cheap source of soft copper pipe I found on ebay what was listed as 9m of soft 15mm outer diameter, 0.4mm-thick-walled copper pipe used as gas lines in boats and motorhomes, and being the only bidder got it dirt cheap. . I picked up an adjustable pipe cutter (3-22mm) for a few quid and measured and cut 130cm lengths. Turns out I was sold around 14m, so had 10 x 130cm, and an offcut.

Unfortunately, though slightly easier than the the half-hard copper, the walls of the stuff I got was 1.5mm so it was still a nightmare, and still came out uneven in cross-section and took ages to flatten. I also found it's expensive stuff to get any more - about £80 for 25m. I'll find a good use for it later on though.

So, time for plan B. I managed to find a site selling 10m x 6mm outer diameter, 4.8mm inner diameter soft microbore copper tubing, so I picked up 6 rolls for ~£42 inc p&p

I then unrolled them, measured and cut into 48 lengths - 16 x 120cm, 16 x 125cm and 16 x 130cm - the difference is because the 48 tubes will be arranged as so, so the outer tubes need to be a bit longer:

The microbore copper is so soft it's very easy to bend and straighten, though it's tricky to get 130cm lengths completely straight. It work-hardens and quickly becomes difficult to bend, though it can be annealed again by sticking it over a gas hob.


Anyhow, I had originally planned to use some of the 15mm pipe I had for the end pipes distributing the water to the 6mm copper tubes. It has a 12mm inner diameter so is a pretty good match for either 7/16" or 1/2" tubing.. After straightening one of the 130cm lengths I bent it to a hook shape over a rolling pin, which was quite tricky. I then cut it to a rough length and measured out the 48 x 6mm holes for the microbore pipe to connect to.

The pipes will have to do a bit of bending at the ends, but hopefully with the small bore pipebender I got this won't be too much trouble, though in reality it'll probably be very very frustrating, since the pipe needs to be bent after the copper fins have been pushed into place.

After lots and lots of drilling here are the radiator end pieces. This would have been so much easier if I had a bench drill and a vice, but as I didn't at this stage I had to improvise:

Plan for pipes joining distributor end tube - side view

After all that drilling my plans changed (always the best way for a project to go horribly wrong). I managed to source some cheap copper sheet for around a quarter of the going rate from shopping around, and for a small extra charge the seller was even willing to cut it with a metal shear into lots of 395mm x 50mm strips for the heatfins. So the dimensions of the whole thing changed, and the drilled pipes were now the wrong size. Ho hum.

I now plan to instead use a plenum akin to those in standard pc radiators. They serve a purpose in allowing a reservoir of water so that water going down the tubes doesn't cause unequal flow between pipes at the inlet end compared to the other. More importantly, it would be easier to make rather than many cramped, fiddly bends for the tube ends.

Here's a picture of the copper. It had been left lying around in a scrapyard for God knows how many years, and was a bit scratched here and there, but should clean up nicely enough.

In the pic are a 39.5cm x 45.5 cm x0.9mm copper sheet for the side wall the tubes go through, 63 of 39.5cm x 5cm x 0.9mm copper strips to be used as heatfins, and 16 of 7.5cm x 39.5cm strips (additional 39.5cm x 5cm heatfins have since been cut from them). There's also some copper bosses (solid cylinders) that I nmay put to good use.


After cleaning

 

[Monkey Puzzle]

Project: Hush!

I then needed to drill 48 x 6mm holes in each of the copper fins and the copper wall. This took a while.

I initially tried using G-clamps and my bench drill and ran into several problems. As the holes were drilled, they pushed a cusp through, deforming the clamped stack. Whilst the cusp/sleeve from drilling is actually useful for soldering and heat transfer, it introduces inaccuracy in the drilling. So I made a jig for putting the copper strips in for drilling.

JIG FOR DRILLING

Sadly the bench drill I have is only 180W, and so lacks the torque to drill large metal holes, so I switched to using an 810W hand drill in a heavy duty drill stand, which allows accurate vertical drilling.

PICS OF DRILLING

After doing some reading up on natural convection and passive heatsink design, I came across a problem sheet set for engineering students on how to optimise the fin spacing for a passive radiator, from a book by a couple of heat transfer professors, and even better, the software it ran on was freely available on the web. So, using the software, I adjusted the parameters to model my heatsink as best I could.

Passive heatsinks rely on natural convection, and this requires the free movement of air over the fins. The fins are much more effective spaced much further apart than in air-cooled heatsinks (~2mm for a Thermalright Ultra Extreme) or even the most sparsely-finned watercooling radiators (~1fin/3.125mm or 8fpi for an RX XSPC radiator).

The simulator models a given width, height and depth of passive heatsink at a given input heatload, and plots the heat transfer of a given fin, and the total heat transfer of all fins combined, at varying fins spacings.

So, whilst the heat transfer for a single fin increases up to a certain point, increased fin spacing means fewer heatfins overall. There's a balance between the two, giving an optimal spacing for a given heatload:

From the simulator there's also another interesting trend - as the input heatload decreases, the optimal fin spacing (fin-pitch) increases, which means I need to optimise the heatfin spacing for the air-water delta T I want to aim for...

The simulator mathematically models a heatsink made from two copper plates held at a set temperature with heatfins that run perpendicular between them, so it's not exactly what my heatsink design is, and in adapting it to model my design I'm not entirely sure how to adapt mine to it, since my design has 48 6mm outer diameter, 4.8mm inner diameter tubes running through the heatfins. I'm unsure as to whether I should adapt it so I equalise the inner heatpipe surface area (4.8mm)to the end-heatplate- to-heatfin surface area in the model, or the outer heatpipe (6mm) surface area... Hope that makes sense!

I altered the parameters to assume just two end heatplates as in the original design, to give a conservative estimate of the performance, and the heatfin spacing (1 heatfin per 10mm, so about 9.1mm between each heatfin). This gave around a 300w heat transfer for a delta of 10C between the air (20C) and the heatpipe/water temperature (30C). But as I say, this is hopefully the worst-case scenario (though the model uses copper-copper joins rather than soldered joints...). A point to note is that the model only calculates the heat transfer from the heatfins - it excludes the heat transfer from the copper tube surface area (~11,000cm^2) and the copper wall (~3,600cm^2).

PIC WORSTCASE SCENARIO (spacing of 10mm on the x-axis)

Adjusting the model to equalise the end plate-to-heatfin surface area in the model with the tube-to-heatfin surcace area gives silly numbers (~560W heat transfer at a 0.5C Delta T, 400W for a 0.4C Delta T).

The real performance will probably lie somewhere inbetween - whilst the best case scenario is probably largely correct in terms of more accurate surface area for the water to transfer heat to the pipes and fins, the model assumes continuous copper joints, and inaccuracies in hole size and loss from soldered joints (~96% tin/ 3.5%Silver/0.5% copper solder) will no doubt lower performance.

Anyhow, enough hypotheticals, here are some pics of where the project is up to at the moment.

After drilling the heatfins I found the holes were marginally too small, using a digital Vernier, in th order of a few hundredths of a mm.

PIC OF DIGITAL VERNIER

So I decided to erode them down slightly by putting them in a drainpipe full of vinegar and harpic toilet cleaner (since it's hydrochloric acid based). I must say, looking through household detergent ingredients for the strongest acid in the supermarket made me feel like a terrorist!

PIC OF TUBES IN DRAINPIPE

PIC OF TUBES OUT OF DRAINPIPE

I then used a microbore pipe bender to make the bends in the pipe. It's a handy little tool, but unfortunately they put far too much paint on it, meaning the measuring bits and the 6mm tube channel was too small, meaning the tube wouldn't get equal pressure around it when bending and would deform too much for my liking. After a quick bit of paintstripping with Nitromors I bent the tubes for insertion into the copper wall. This was a bit fiddly; in order for the bends to line up exactly with the drilled holes I needed to know amount of length the bend took. After a few annoying mishaps, annealing and restraightening I got the tubes bent accurately.

 

[Monkey Puzzle]

After inserting all the tubes I could then start putting the heatfins on.

I ran into a bit of a problem when putting the fins on - they're a tight fit and the smallest angle off horizontal, or pipe angle off vertical means they can be tricky to get on. It's a bit of a trade-off between tight fitting fins with minimal gaps (less solder and better heat transfer) and ease of putting the thing toether. The fins are pretty tight, and in gently hammering them ona few of the tubes were pushed too far down, which you can se in the pic. Luckily, using the pipe cutter without the cutting blade inserted it's possible to grip the tube and push it back through the heatfins.

PIC OF PIPE CUTTER MINUS BLADE

There's only 11 heatfins on in various temporary positions (finished article will have 74 fins);

PICS WITH HEATFINS

I've just got the solder and flux and need to make a watertight box tonight to deoxidise the copper in a vinegar bath before, and after soldering them with a propane/butane blowtorch, since it'll oxidise all the surrounding copper. Anyone know of a place I can get lots of cheap, relatively strong acid? Not sure where to get it and any regulations - was told by a car bits shop that they can't sell battery acid (~35% sulphuric acid) these days. I could probably make do with distilled vinegar but it'll be expensive for the amount I need and take a long time as it's weak.

Any questions just ask.

 

[Monkey Puzzle]

reserved..

 

[Monkey Puzzle]

reserved....

 

[Monkey Puzzle]

Man that looks awesome, should provide more than enough cooling.

Hopefully! - the finished thing will have around 40,000cm^2 of copper surface area (for comparison a TRUE has 7,500cm^2 of aluminium )

 

[Monkey Puzzle]

Thanks for the nice comments.

Good shout, but more importantly well executed. I'm curious as to how you're going to solder all of these, one joint at a time? You're a patient man if so

Impressed by the design. Bit late now, but if you fill copper pipes with salt and cap the ends you'll find bending them easier. Sand works too, as does water, salts just the most convenient.

Will the case be the only radiator, or will you have one or two conventional active ones present as well?

The plan for soldering is going to be to bath in vinegar, then brush flux on around the joints and put rings of solder around the joints of maybe 5 fins at a time and then blowtorch the fins, before deoxidising in a vinegar bath again.

The blowtorch is supposed to get copper pipe up to around 650C, but the heat is going to be dissipated, which is what the thing's designed for after all! So hopefully the heat will spread but also get slightly above the melting point of the solder (~217C). It's not really something I'll know until I put the torch to it - I can't test what temp it'll get to and how easily on scraps of copper. Even if the plan works out, it's going to take a long time to solder...

No plans for other radiators - this should hopefully be sufficient. One advantage of switching to using a plenum (hopefully CNC cut by a friend from a block of acrylic) is it allows the possibility of splitting the radiator into two loops in the future without too much hassle.

Will also have to see what the pressure drop is going to be like - it's designed for the tube resistance to match that of 1/2" tube (resistance of 49 tubes of 4.8mm internal diameter in parallel is equal to 1/2" ID) but the water still needs to go through 120-130cm of tube and a few gentle 90 degree bends. The plan at the moment is to have an XSPC Edge, MCW-60 and use a 10W DDC for quietness, but I may be able to mod it to 18W should the need arise (haven't opened the DDC to check if moddable).

Just measuring up a 2mm sheet of perspex atm to bend it and make the watertight innards of a shallow (~6cm) bath...

 

[Monkey Puzzle]

I wouldn't know where to start calculating that, it's going to be flow dependent for one thing.

That's true, though the flow rate (velocity) of the water in the 4.8mm ID tubes is about a sixth that of the water in the 1/2" inlet since the cross-sectional area of the 48 combined tubes is 868.6mm^2 vs 126.7mm^2 for 1/2" tube.

Assuming laminar flow?

Yes, based on a quick and dirty pipe-flow online calculator. But it doesn't have the function of introducing bends, so it's based on straight pipe.

I had a brief play with numbers, and the closest I could come was the resistance of the 49 tubes is about half that of 1" inner diameter tubing based solely on ratio of cross sectional areas.

The pressure drop of water in a straight circular tube depends upon the tube diameter, length, and volumetric flow as given by the Poiseuille equation (delta P = (8 x mu x length of tube x volumetric flow)/(pi x tube radius^4).
mu is the dynamic viscosity (Don't ask me what it is exactly!). So halving the tube radius increases the resistance 16-fold. Who'd have thunk that basic fluid dynamics we were taught for haemodynaics would come in handy?!

Flow down 4.8mm tubes is going to be pretty turbulent at the best of times, which is great for heat transfer but ruins me mathematically.

It's actually the other way round - larger diameter tubes actually convert to turbulent flow at lower flow velocity, because there's a bigger difference in velocity between the 'laminae'. I'm not worried about turbulent flow - there may be some at the bends, but it'll soon re-establish laminar flow after the bend. What does concern me is the frictional pressure loss from the sheer surface area the water is in contact with, and the length of the tubes (around 120-130cm).

How big is the copper structure? It's very hard to judge from the pictures.

39.5cm x 45.5 x ~45 atm (some tubes need trimming).

If possible, which it looks like it might be, Id suggest (after vinegar) putting a ring of solder around each and every joint, then sticking the entire structure into a household oven at 230 degrees. If it fits, all you have to do is check every couple of minutes and the entire thing will solder itself together for you. if it doesn't fit, befriending the local pottery group and borrowing their kiln would be an alternative.

Good suggestion! It's too big for our oven, and besides, our oven's dodgy and takes ages to cook - due to a furred up gasline I think, since the last one had the same problem. I doubt it could get up to 230C. I think other home ovens would have the same problem - I'd planned on doing it that way but from my calculations it would take a kilowatt oven about half an hour to get up to temperature, assuming no heat loss, and was told solder flux should get to heating temperature within 6 minutes.

A kiln would no doubt have no problem though, since I'd think they use a heftier heating element, though I could be wrong.

I had thought about getting it put into an oxygen free oven, but I can't find anywhere vaguely local, and it would probably cost a fair bit to get them to stick it in the oven..

Heating it with a blowtorch will require a massive blowtorch or considerable ingenuity. Soldering a heatsink is, as you've noticed, not so easy. How does sitting it on an electric hob sound? Keep all the copper reasonably hot, turn a blowtorch on the part you're soldering. Heat wont dissipate anything like as fast if the temperature gradient is less

Don't have an electric hob unfortunately. I'll try the blowtorch and let you know how I get on.

 

[Monkey Puzzle]

Glad to see you ditch the idea of trying to get all the small bore tubes to meet up with a large bore tube drilled with umpteen holes whilst also having to fiddle about bending the ends to suit, that would have been an absolute nightmare. By plenum I take it you mean a rectangular manifold?

Also, you say this is also going to form the case of your pc, where is the mobo going to lay,? Is your first pic showing how it will sit, i.e. the mobo tray horizontal above the bottom fin array?

The motherboard tray will be vertical; I'll post a photo up later with a rough mock-up how the motherboard tray will sit.

Didn't have time to read all the posts, but if you are still using the 8-9mm copper tube and you used a pipe cutter on it, it's probabbly not a good idea on such small bore pipe.

The pipe cutter will push in the end of the pipe and possibly reduce the diameter to 6mm or less on the ends.

If you do use a pipe cutter on this size of pipe, try to ream out the ends well, although I would strongly suggest using a junior hacksaw to cut it and using a fine file to clean up the ends, both internally and externally.

Thanks for the suggestion. The pipe cutter does leave a big ream on the ends (though it doesn't deform them). I need to trim the tubes down later anyhow (possibly with a dremel as the mini pipe cutter won't fit as the surrounding pipes are in the way), so I'll take a small spindly file to them when they're at the final stage.

 

[Monkey Puzzle]

...

 

[Monkey Puzzle]

How much planning was put into this project out of interest cause it seems like a lot

Quite a bit - lots of reading up on stuff and trying to find parts on the web mainly. The actual design changed around a few times for what sides of the case would be heatsink, and motherboard orientation.

looks huge

How much did all that copper set you back ?

MW

Around £160, though on the plus side it's probably worth about that as scrap copper. Copper's expensive stuff, and I'd planned on using thinner sheet due to price - for the amount I needed it was looking like around £300-400 for thick copper sheet so it didn't figure in my plans. But then I found a really nice guy on ebay selling several large sheets and who was willing to cut the sheets to size. He offered me commercial funding; I think he thought I was making a prototype to go into production!

 

[Monkey Puzzle]

have you thought of heading down the scrap yard and enmptying out some batterys? im sure the scrappy wont mind you having the old batteries to drain, at a price of course. even a diluted amount will be stronger than vinigar

A cunning plan - I'll look into it - using a vinegar/harpic power plus mix atm I had leftover from earlier - seems to do the job but leaves the copper a very slightly bluey-pink..

That was a very detailed reply, thank you man. I'm studying engineering, but fluid dynamics is not my strong point. I'm very glad you've run the numbers on it before starting manufacture, any estimates for the heat it can dissipate?

Not entirely sure tbh - the best-case scenario from the simulator gives stupidly high heat dissipation (500W+ for a 0.5C delta T) which I'm not entirely sure is just from assumptions made in the model which by adapting it I've violated.

Worst case (modelling the combined 48 x 6mm x ~0.9mm (=~800mm^2 ish) pipe-to-heatfin surface area, with the surface area the heatfins would make with the hotplate at the end in the model (50mm x 0.9mm x 2 = 90mm^2) gives around 300W for a 10C delta T. It should hopefully perform much better than that, despite lowered performance from largely tin solder (the solder has a thermal conductivity around a quarter that of copper).

Getting flux up to temperature in 6 minutes shouldn't be a problem, whack the oven up to full temperature until it finishes warming up, then swiftly put the copper into it. If it doesnt fit then no luck though, which is a shame. I hope the blowtorch works out for you.

Bit more ambitious, and in several ways a quite stupid idea, but you could heat it electrically. Mains ac will make things quite hot. I succeeded in welding a small piece of aluminium with it before the circuit breaker went. Mains ac hurts mind, and passing current through a large copper block will be considered unsafe.

Regardless I look forward to the next update

Lol, I had considered this, but then my sense took over. I have a feeling there's no way on earth that the current would be high enough - copper's not the best resistor in the world!

I also considered sealing off the tube ends and superheating water, but it would have inevitably ended with a "hai guys, I just blinded myself with highly pressurised steam" post.

I also looked into a soldering clamp tool called a hotdog2 that uses an electrical heating element and clamps around the bit of tube you're soldering, but it didn't seem to do 6mm and costs about £100, plus it's meant to go around the outside of pipe fittings being soldered, which mine aren't, so it would probably get gunked up with burnt flux etc.

Anyhow, the blowtorch seems to be working okay - gets up to temperature without too much trouble. It's a painfully slow process of putting the heatfins on, deoxidising etc.

I am becoming more intrigued on how the soldering is going to be done as it looks to me that getting all those plates to line up and pressed into place is going to be a very tricky job, which will get harder as you put more plates on and the thing stiffens up, unless everything is absoutely dimensionally **** on. Have you considered making the holes in the plate a fair bit larger to make fitting easier, then using copper washers to bridge the gap? You could offer a plate up to the tubes, clamp it up, put the washers on, draw round each washer, take everything off, solder the washers to the plate in the exact same position, so that when you offer up the plate again it should be tailored to the tubes. Just have to use washers which have a inner hole dia close to the tube OD. With the plate in place solder the washers to the tubes, the washers may well unsolder themselves form the plate while you do the second solder run but if you clamp the plate and do them one at a time it shouldn't matter. Then repeat this for the next plate.

at JonJ's mains AC idea! In words of Sergeant Wilson "Do you really think that's wise sir?"

edit: Just thought how my idea could be improved. Why not fabricate your own squaure washers using the flat plate you already have. Cut the plate into squares, coat one side with flux and seed with solder so you have a square of copper with a film of solder on one side. Then drill a suitable hole in each washer. Pre-soldering each washer removes to need to put the loose washer on and draw round it, you should just be able to put the pre-soldered washer on the cooling plate as positioned on the tubes, and blast it with your blow torch. The solder may even run around the tubes as well, though it will probably still be necessary to put an additional ring around each tube. The key benefit of this is you can enlarge the holes in your cooling plates so that they will be more forgiving to any measurement errors.

Thanks for the suggestion, but it sounds rather fiddly. I'm using 9mm thick wooden spacers atm, which seem to work okay - I'll do an update later with pics.

 

[Monkey Puzzle]

UPDATE 1

Roughly how the removable motherboard tray will sit (looks a little tighter height-wise than it will be due to the top pipes being a little bent down atm). The PSU will sit behind at the bottom, fan facing down.

A sheet of 2mm styrene that was lying around:

Heatgun:

Bending:

A quick and dirty tray to bath it in. So quick and dirty that it leaked, so it has an outer box lined with plastic sheet a mattress came in - now it's in the styrene tray to avoid cutting up the plastic lining:

Deoxidising:

Shiny:

Making solder slinkies.

After cutting to solder rings - not sure how many are in the bag, probably a thousand or so.

Blowtorch - gets up to temperature okay.

Various bits for putting fins on and soldering:

Fin in place with 9mm thick wooden spacers for straightening the fins (they need to be hammered gently into place and deform a little in the process)

Solder rings put around the pipes - it's quicker to put them on like this, with a fin above, near the pipe ends, as it made putting the fins on a lot quicker.

Solder rings after tightening with needl-nosed pliers (surprisingly quick and easy).

A freshly soldered fin on top: The fins are a bit rainbow coloured from scale slowly being removed by the weak acid bath - hopefully it'll all go - the bottom fins are quite pink. It was pretty disconcerting to see the shiny copper scale up and get covered with burnt flux, as it didn't seem to get removed at first. I'm a bit concerned about the acid possibly attacking the solder joints - I may switch to cleaning it only at the end when all in place and using a fine wire brush to clean the pipe before soldering.

Unfortunately I couldn't correct the bend that got pushed too far through (3rd from the left at the bottom). A few of the first fins are a little bent as well, though they'll be mostly out of sight behind the motherboard tray.

 

[Monkey Puzzle]

Great work you have done there.
How are you going to get rid of the burnt marks on the copper?

Well it's a combination of oxide and burnt tacky flux - it seems to go after a long time in the acid bath, but failing that I may be able to clean it with a large ultrsonic cleaner my brother is planning to get. I say maybe as the dimensions of the internal tank of one is 395mm wide x ~540mm x 300mm deep, so would be a very tight fit indeed to clean all of it. The other he has his eye on is larger and wouldn't be a problem getting it inside. They're very good at cleaning:

 

[Monkey Puzzle]

Not that much progress - i've been away work shadowing for 2 weeks so haven't been able to get that much done since the last update - I'm up to 34 fins soldered on, so around halfway through atm. I wasn't happy putting it in the acid bath repeatedly so I switched to using strips of 120 grit wet and dry to sand around the pipes to be soldered, putting a couple of fins on, soldering and then repeating. It's a painfully slow process.

Just waiting on the ultrasonic cleaner to arrive later today. Hopefully it'll clean up nicely (without breaking any solder joints, which is a myth apparently) and mean I don't have to sand the pipes after every couple of fins. I'll try and get a video of it in action later on today.

 

[Monkey Puzzle]

Monkey Puzzle, what conditions are you using for the fin tip? As far as I am aware there are three cases, when the fin is very long, when the fin is adiabatic and when the fintip has the same Heat Transfer Coefficient as the fin.

You'll do yourself wonders if you were to consider this a 1 dimenional problem. I.e. The conduction is along the axis of the fin and the HTC (heat transfer coefficient) is constant.
Are you using forced conduction and fully rough turbulant flow?

I've done a fair few experiments in labs and wouldn't mind talking to you to see what kind of challanges you're overcoming and possibly input anything.

That's really nice of you to offer - the radiator's nearly finished so I can't change the design or anything, but I don't suppose you have any experience of usinga program called EES (engineering equation solver)? It's used to accompany a book called Heat Transfer by Klein and Nellis, published by Cambridge University Press.

It has the equations used for natural convective heat transfer and the problem I've adapted (Heat transfer option at the top, chapter 6, example 6.2-3), which you plug numbers into for the dimensions of the heatsink, fin pitch (spacing) and fin width, and it calculates the results and allows you to plot them. It can be downloaded here if you fancy taking a look - the trouble I have is I can't find what equations it uses to calculate results, and so I don't know what assumptions it makes other than it treats the heatfins to be the same temperature throughout (stated in the problem sheet that loads with example 6.2-3). I don't think that is a problem for my radiator design since the pipes are spaced about 2cm apart (edge of one pipe to closest edge of the next), but by trying to adapt it for the greater area of 48 tubes transfering heat to the fins compared to a hotplate at the 2 ends in the model (by reducing the distance between the two hot endplates and increasing the width to maintain fin surface area) it gives unbelievable results and I'm not sure why. If you're able to work it out I'd be very impressed.

Edit: Ahh, you're using passive convection! I'd be really interested to see what heat transfer coefficient you've ended up with. You'd get a better velocity and temperature profile for forced convection.

Yeah, interested to see how it does myself! It will have space to fit 18 120mm fans if I really wanted to, and though the fins are spaced 2.5fins/inch so screaming deltas probably won't gain much above quiet fans, the overall surface area of the finned part plus tubing going through the finned part where fans blow is about 37,000cm^2, so around 5x that of a TRUE, plus it's copper - might go crazy and try it out at some point in the future!

 

[Monkey Puzzle]

Btw, does anyone have any experience of brazing copper, or soldering copper radiator innards? I'm making a copper rectangular box so need to attach the sides by soft soldering with tin/silver/copper solder (96%Sn,3.5%Ag,0.5%Cu) if I can - I presume that galvanic corrosion won't be a problem since Copper and Tin are close to each other on the reactivity table, but if anyone thinks it will be a problem or has experience please let me know! I'm not sure the blowtorch could get anywhere near brazing temperature (~850C) but hard soldering with silver solder may well be possible (650C ish) since the propane/butane blowtorch is rated at getting copper pipe to around 650C. Alternatively, a friend has a TIG welder... but I'm not sure that is sensible and don't want him to hand me a melted lump of what was once a radiator!


I'm nearly done with making the radiator - 69/74 fins done so at the ends where the plenum/manifold will be.

I decided to go the route of having a copper rectangular box at the top and bottom for the manifold. It won't be as pretty as acrylic block, but trying to get a good seal and screws in the 5mm edge around the pipes just doesn't seem feasible, unfortunately, and I have 4 copper fins that haven't been drilled to use, so no extra cost. Plus, time is against me, and a copper manifold is quicker and easier to make: I need to finish this project before the end of the month really, as I'm moving for my job and won't have access to tools.

I'm getting a friend to mill holes in copper cylinders for the inlet, outlet, fill port and drain port this weekend hopefully, which will then be tapped and joined.

 

[Monkey Puzzle]

I have no idea what you are doing here it looks like a giant version of my cpu cooler but in copper...

Yeah, that's sort of what it is, but cpu air-coolers use heatpipes (containing water at low pressure) whereas this is a water-cooling radiator so has water running through the pipes.

Been a while since I last looked at this!! Hope its still going well Hope the ultrasonic cleaner can clean it up nicely, would be the easiest way by the looks of it!

Good luck with the rest of this, seriously an impressive build!

Cheers man; almost all the fins are on - just the end-fins and the rectangular plenum/manifold boxes to go on the ends plus inlet/outlet/drain plug/fill-point to be soldered on. Unfortunately my friend is waiting on a new motor for his lathe so don't have the ports back yet.

The ultrasonic cleaner didn't do that much, but tbh I don't know what cleaning solution to use - washing up liquid didn't seem to do much and I don't want to ruin the solder joints with acid.

I figured updates would just show more fins on at this stage, so not that exciting really.

 

[Monkey Puzzle]

Time for an update.

I changed the method by which I put the fins on;- before I had deooxidised the copper pipe prior to putting new fins on, now I instead changed to using strips of 120 grit wet'n'dry with sellotape on the back to strengthen, which I used to sand about 4cm of the pipes, flux and slide fins on (I had already filed the holes of):

PIC OF SANDED PIPES

All the heatfins are now on, and the pipes have been trimmed down.

PICS OF MONSTROSITY

I've decided to make the manifold/plenum from copper - it'll have an inner box made from thin copper (0.152mm thick) joined to the end fin by solder paste, and strengthened with some of the thicker 0.9mm thick copper made from 4 leftover copper strips I had.

My friend Robin has some nice tools and machines, so I asked him to maked the inlet, outlet, fillpoint and drain port for the radiator from the 25mm diameter copper bosses I had.

PIC OF LATHE

After making 11.8mm holes with the lathe the copper bosses were tapped on the lathe with a BSP 1/4 tap, cut with a circular saw mill bit and then fly-cut on the mill to give a beautiful smooth shiny surface, which doesn't really come across in the photos:

MACHINING

PORTS DONE -

I'd bought a roll of thin copper when I started the project:

PIC OF COPPER ROLL

PIC OF ROUGHLY HOW THE BOX WILL GO TOGETHER
The sides look angled and messed up at the moment, since only some of the flaps of copper have been soldered together. I need to be able to open the box at this stage in order to press it against the end-heatfins to make good contact when being soldered to the side of the box with the slits (the pipe ends will protrude through these slits). The rest of the thin-walled box will then be closed up and soldered into place, and reinforcing 0.9mm copper strips soldered to the outside of the box and the inlet, outlet, fillport and drain port soldered on.

Sadly the project will have to take a short hiatus since I'm moving away for work next week and won't be able to take it with me, so finishing it off will have to be done when I can take a week's holiday.

 

[Monkey Puzzle]

Looks great and can see a lot of max hours gone into it!

Yep, a lot of hours. Annoyingly I won't be able to get time to fnish it for a while, but there's not that much left to do - the trickiest, most time-consuming parts have been done.

Amazing. But how are you going to connected all of the tubes to the res? And to the components... and isn't it going to take one hell of a pump to get all the water around? Or do you want to use natural convection? Also, since it's copper i'd hope you were using anti corrosive fluid, and given how expensive it is and how much of it you'd need... bye bye wallet

The box with the slits in one face is the plenum/manifold. The side with slits in is going to be soldered to the end heatfin, so that the pipes are inside the manifold/plenum and sealed.

It shouldn't take too strong a pump to get water round it, but in all honesty time will tell.

Have you got an illustration of what its going to look like when its finished?

I'm going to keep that as a surprise - it's more interesting seeing something you weren't necessarily expecting imo. I got a load of aluminium angle and flat bar/plate last week to make the supporting frame...

I mean looking at those pics its already the size of 3x mid tower lian-li's its going to be mahooosive!

Nah, it's only a bit taller than the pc-7 in the pics, and twice as wide (~45cm wide).

Looking great btw

Cheers!