titanium heat exchanger help

[nanook ofthenorth]

Hey, going back to the origional post on heat exchangers rather then working with Ti —
The Heat Exchanger in the House video was made by MSR a few years ago, part of their Superfly stove hanging kit that they made a few years ago.
I actually got a hold of one a year or two ago and have been really impressed with it on a gas stove. BTW its a thin springy Al sheet, not Ti.
For canister stoves I prefer the Ortik, the old MSR doesn't fit on smaller pots and I just like the Ortik more for stability/use in a tent/wind. The current MSR exchanger is nice for heavy camping.

I think both are disposable though – light Al or Nomic fabric subjected to cyclicalic heating (maybe at a higher heat for the MSR then the Ortik), means that at some point they are going to wear out/burn up.
At least for thin pots they have water in them to keep the temperature around 100C so while I'm not worried about my pots burning up, the Ortik and MSR heat exchangers are more like those MSR Al windscreens that need periodic replacement.

If thin, light Ti has a higher melting point and can handle the heat of an XKG or Simmerlite better then Al then I think there is a reason to try it, otherwise just get yourself some circa 1mm Al spring sheeting and bend it to shape.

Cheers, R

[Josh Leavitt]

David

:-) your feet are getting colder.

Evan

Nice! link, brazing would be a really good way to join Ti to Al, but not so easy to accomplish. With such good surface contact, heat tranfer would be really nice.

[Evan Jones]

keep going…

http://www.innovationcooling.com/overview.htm

[Josh Leavitt]

Its an insulator, am I missing something?

[Evan Jones]

diamond is an electrical insulator, but the best thermal conductor – compare with silver.

folded fin he with aforementioned thermal grease, fillet brazed to ti pot. if anyone is crazy enough, cu plate your material of choice and the pot bottom too. certifiably insane options are available for those with too much time and money

[Josh Leavitt]

Evan, I got it now.

[Mike M]

Bill- that's some fancy bending work there- good job! :)

I found a decent pic of the old MSR exchanger (and hanger)- now if someone could figure out how to build one :)

[Roger Caffin]

> brazing would be a really good way to join Ti to Al, but not so easy to accomplish.
You wish!
I am not aware of any brazing material which will work with either titanium or aluminium.
You can get an aluminium 'alloy' which will bond to some aluminium, but not to Ti.

Cheers
Edit: see below for a correction to the above re titanium – if you can handle the complexity.

[nanook ofthenorth]

Hi Mike – see my post above for advice on the old MSR exchanger.
Thin springy Al, or strip down the current one.

[Josh Leavitt]

[Mike M]

Robert- I'd like to try and replicate the MSR one pic'd above in Ti- any chance of taking measurements and/or a few pics

I searched around a bit for anyone still selling them, but came up empty

thanks

Mike

[Roger Caffin]

Hi Josh

That is not brazing to titanium. That is brazing to copper which has been electro-plated onto the titanium. A bit different.

OK, it is possible to solder or braze to titanium under very special conditions. For instance, if you plate copper onto the Ti base:
'Soldering is best carried out with lead-tin-based solders at working temperatures between 200 and 300 °C after the contact surfaces have been electrolytically or dip-coated with copper or silver to improve wettability and adhesion.'

If you don't mind the difficulties and the temperature requirements, brazing can be done using either silver or copper alloys, provided you avoid forming intermetallics:
'The copper-titanium alloy CuTi30 can also be used to make high-strength brazed joints but the disadvantages here are high joint preparation requirements, occasional brittle phases in the joint and damage to the base metal.'

Tricky stuff, and not really suitable for MYOG at home!

Cheers
(Quotes courtesy Deutsche Titan.)

[Josh Leavitt]

Roger

It gets done above 840* so it is brazing. The Ti is not electroplated with copper. That was done in a vacuum, but there are Ti brazing techniques that can be done in open air also. Open air techniques require neutral flames, similar to those used for al "brazing". I believe I already stated that it was not "easy", but that is a relative term, even for MYOG.

[Josh Leavitt]

Mike

I just realized that this thread was started some time ago, and Carlos may not see my offer for ti. I dont know anything about titanium, but I'll give you some .005" ti foil to build a heat exchanger, just let us know how it goes.

[nanook ofthenorth]

Mike, its slightly shorter then my 2L MSR Ti pot, dimple are 1in out from the pot max and come in every 10-12cm. I'd say give her a go with some thin springy Al sheeting, dont think it should be too hard…
Failing that if you stripped down the current MSR heat exchanger I think you would have something similar too

[Mike M]

Josh- sounds good, I'll send you a pm :)

Robert- thanks for the dimensions, I don't have the MSR heat exchanger- looked at it, but too heavy imo

[Mike M]

big thanks to Josh for graciously sending me some ti foil! :))

the ti is 4" high, which looks to be just about perfect for my pot (2.0 MSR)- leaves ~ 1" above the exchanger when the exchanger is flush w/ the bottom

a few pics (sorry some are blurry)

side view of exchanger

from bottom

nested in pot

weight a svelte 1.4 oz :)

now the question, does it actually work :)

I'm going to try and do a few boils (keeping everything the same- amount/temp of water/ambient temp/etc) w/ and w/o and see what if any differences there are

I'm assuming if it speeds up boiling any, then it should also speed melting of snow?????? I could try some melting snow tests, but seems like there is more variables w/ that sort of test

anywho- I'm happy w/ the way it came out, looks very similar to the one that Steve House built and the one MSR used for awhile

Mike

[nanook ofthenorth]

Looks good! Glad to see there is an alternative for when my MSR bites the dust.
FYI- I wasn't really recommending the current MSR, more buying it and then ripping off most of the reinforcements/junk on it and stripping it down. That might also work if your having trouble sourcing metal.
I definitely dont have a testing setup so be interesting to hear what you see – my thoughts is that it is slightly less efficient then the current MSR. It also helps if you overlap the exchanger and windscreen.

[Mike M]

yeah I'd bet good $ that the MSR exchanger is more efficient, but at 6 oz it better be a lot more efficient :)

my testing won't be nothing very scientific, but hopefully will see some differences

I might have to play around a little w/ the positioning of the exchanger- I'll be using the MSR windscreen that came w/ the Windpro- it's high enough it comes up a little on the side of the pot

[Kevin Beeden]

I think it's unlikely that this design of heat exchanger, implemented in thin Ti foil, with so few contact points, and such poor thermal contact (lightly sprung contact) will actually transfer much heat to the pan by conduction from 'heat exchanger' to pan.

What it might do is to hold the hot gases close to the pan, thus increasing the heat transfer from gas to pan; basically, acting as a windshield.

You might like to have a look at my SqueezeBox Stove idea.

A couple of SqueezeBoxes have been built in Ti foil (the Cicerone guidebook writer, Paddy Dillon, uses one he copied from an Al one I made him), and Steve Evans very kindly made one for me using his water-jet cutter (sadly, neither of us were happy with the end result), which I still have to fold up.

[Mike M]

nice work! :) it would definitely be tougher to replicate w/ ti (vs al), simply tougher to make bends/folds w/ ti- but possibly doable

that design does share a lot more w/ the MSR heat exchanger design than the one I built, I still haven't had a chance to do any testing- last weekend it was bitterly cold on Sat, and very windy on Sunday- hope to give it a go this weekend

[Kevin Beeden]

… for sounding a bit negative last night; that's just my posting style, especially when rushed trying to cram in the 'technical bits'…

I certainly like the simplicity of your method. Am I right in guessing that the curve is the 'natural' curve of the rolled Ti foil? Or did you have to curve it somehow? Or is it simply the result of bending the folded sheet around the curved surface? It's the latter, isn't it…? (d'oh!). The method might well be applied to making a SqueezeBox, replacing the outer folds with simple bends, as it's the opposing bends that make folding difficult…

The SqueezeBox might look more like the folded MSR HX, but, like yours, it provides almost no genuine conductive heat transfer to the pan; in fact, the upper windshield doesn't touch the pan at all (it needed clearance to provide adequate gas flow to ensure clean combustion). I'd not seen the other MSR 'HX' before.

Looking at the MSR 'proper' folded HX in detail for the first time, it looks unnecessarily complicated to me; why the complex outer strap design (why not a simple, central, thin strap)? why the multiple riveting of the outer strap to the HX? why the complex closure (why not use a simple toggle clamp?)?

[James holden]

looks good mike … the proof is in the pudding though …

you should be able to conduct boil temps outside … the water should boil faster with less fuel if it works

marketing hint … if it works send steve house a free sample … even if you arent planning to sell it, no one else will put it to better use and test it in harder conditions ;)

[Mike M]

Kevin- yup the later :) I was thinking the same thing on the "squeeze box", just get the spacing correct and make it simple folds around the pot. it would weigh a little more than my rounded bends, but shouldn't be overly so.

I agree w/ your assessment of the MSR- overly complicated (and as a result pretty darn heavy)

eric- yeah- if it boils quicker (I plan on weighing the canisters as well to see how much fuel was used as well) it should be relatively simple to calculate whether it's worth packing the extra 1.4 oz on a x day long trip.

Steve swore by his, mine looks very similar (it appears I might have one or two additional bends in mine)- he'd definitely be the guy to put through real world testing :)

[Mike M]

my not overly scientific results :)

I boiled 1 liter of water of cold tap water (~ 45 F) to a full rolling boil, temperature was 27 F, elevation 2400'

the canister was weighed before and after each boil

stove is a MSR Windpro (canister inverted), pot is a MSR 2.0 liter w/ lid, the provided windscreen was used which includes a small circle of foil that sits under the stove

the heat exchanger was ~ 1" below the pot- not sure if this is the optimum location but someone mentioned previously that having overlapped works best

boil time w/ the heat exchanger was 6:10 minutes, fuel used 14 grams
boil time w/o the exchanger was 6:44 minutes, fuel used 17 grams

certainly not a night and day difference, but a ~ 18% savings in fuel and a ~ 9% quicker boil (not sure why those aren't the same or closer???)

theoretically after 13 boils you should be in positive territory (weight of the exchanger is 1.4 oz)

it's possible that the heat exchanger may possibly even add more efficiency w/ melting snow vs full boils, w/ more of the heat going up the sides?????

I think that will be next test :)

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