titanium heat exchanger help

I've done some searching for titanium sheet myself and the thinnest I've been able to find is 0.004 in. from a seller on Ebay. I used it on my wood-burning camp stove. It's the 15-3-3-3 alloy. I've also seen 6Al-4V alloy titanium in 0.005 inch thick sheets on Ebay.

I don't use a traditional heat exchanger anymore because it seems that they are meant to serve two mutually exclusive purposes. They conduct heat from stove exhaust gases to the pot sides, and they trap those gases against the pot to reduce heat loss to the atmosphere.

For conducting heat to the pot from the hot stove exhaust, it seems that something with a high thermal conductivity, like aluminum, might be a good choice. But for making a thermal barrier between the layer of stove exhaust rising up the sides of the pot and the outside air you'd want something with low thermal conductivity. You'd also want the outside surface of your heat exchanger to be shiny, to reduce radiant heat loss.

Titanium has very low thermal conductivity and high emissivity, which means it does a poor job of conducting heat to the pot and gives away a lot of radiant heat to the surroundings. Aluminum is not only less dense (it doesn't need to be strong), but it has low emissivity (it doesn't give much heat away by radiation). Aluminum also has high conductivity, which is good for moving heat from the stove exhaust to the pot, but also good for moving that heat to the outside air.

So I split it up on my stove. I use shiny aluminum fins (folded foil) to transmit heat to the pot, and a metallized Kapton shroud with kiln-paper (ceramic paper) lining to reduce heat losses to the air. The whole arrangement weighs 55 grams, or 1/3 the weight of the MSR heat exchanger.

> use shiny aluminum fins (folded foil) to transmit heat to the pot, and a metallized Kapton shroud with kiln-paper (ceramic paper) lining to reduce heat losses to the air. The whole arrangement weighs 55 grams, or 1/3 the weight of the MSR heat exchanger.

Pictures?

Cheers

Carlos
Have you considered the Heat It version from http://www.ortik.net/ ?
At 138g it's not UL but it is a lot more versatile by allowing baking (or as a "cozy") and hanging the stove as well as a wind shield/heat retainer.
Franco
( looking at your avatar made me think of that one…)

I've tried to buy one. No luck. If anyone can get a respose out of Ortik, let me know, I'd love to get one.

Roger,

I'll take some photos and post them, but it might not happen for a week or two.

Franco, the ortik looks a good idea, last year I tried to find info about the company because is a Portuguese company and I live next to the Portuguese border and I frequently work there but I was unable to find a contact.

Anyway my first idea is to find a UL cooking system suitable for high altitude (Im planning one trip to Nepal with some members of my mountaineering club to climb some non technical peaks)

(my idea: stove, aluminium pot with lid (antigravity gear or msr titanium) heat echanger (titanium brass or aluminium) msr pot grip, BPL spoon/fork and aluminium foil wind screen.

I have serious doubts about including a cozy for the pot

and of course i accept sugestions ;-)

I probably choose one msr windpro stove (lightest canister stove with preheater to be used with an inverted canister) and I don’t think that this stove is compatible with the ortik.

And I expect that a simple heat exchanger would be much lighter than the ortik.

Colin, thank you for your reasonable ideas, may be one aluminium exchanger could be lighter cheaper and more efficient,

As roger I’m really interested in that photos too

Thank you

Hi Carlos

> Anyway my first idea is to find a UL cooking system suitable for high altitude (Im planning one trip to Nepal with some members of my mountaineering club to climb some non technical peaks)

When I was there (some years ago now) it was rather hit and miss whether you could find suitable gas canisters for sale. You can't bring them in with you on the plane of course.

However, kero is available – very widely, and that is what most parties rely on. The Nepalese people use it for cooking and lighting.

You could do worse than to bring something like the Brunton Vapor AF with the fuel bottle cleaned out and full of water. That way you can use canister, white gas or kero and necessary. It's a good stove.

Colin,

I am trying to find/make a light heat exchanger to use with a Windpro remote canister snow-melting set up. I've heard that heat exchangers can 'pay for themselves' in fuel savings after a few days on the trail. Your design sounds intriguing. Could you shed some more light on the design and/or post a few pics? I'm looking into securing some of the Kapton, but know nothing about it, so could use a little guidance on the design.

Thanks!

John

John,

I never did get around to taking photos of the set up I had when I put up that post almost two years ago. I'm still experimenting with Kapton film. The stuff I have is 1 mil (25 micron) Kapton HN and is reinforced with a very fine fiberglass grid. It is aluminized on one side. When the reflective side faces the stove, I find that I can keep it pretty close to the flame without any apparent damage to the film. The published maximum continuous use temperature for this film is 710F. Like Mylar, though, Kapton film tears pretty easily once nicked (although much less easily than aluminum foil), and I think the 1 mil stuff would be too thin if it weren't for the fiberglass reinforcement.

I have also tried making silkevlar, for the same purpose (windscreens for stoves). Kevlar coated with high-temperature silicone could withstand much rougher treatment than the Kapton and would tolerate similar temperatures (almost 300F higher than silnylon).

I ordered some 0.8 oz kevlar fabric from CST Composites, and some Duraseal 1531 high temperature silicone from Cotronics. I applied a thin coating of the silicone to a small sample of the fabric and compressed it in a vise overnight. I tried this several times and was not able to get any of the samples to come out lighter than 5 oz/yard. The fabric is for composite layups and is not tightly woven or dimensionally stable. It resembles a screen (80 threads/inch) and the silicone has to fill the large spaces between the threads. I think this approach might have more promise if lightweight and tightly woven fiberglass or aramid fabrics were available.

Would this help?

http://www.titaniumgoat.com/windscreens.html

http://www.suluk46.com/RandD%20-%20RD1%20Ti%20Wood%20Stove.html

Colin: "Aluminum also has high conductivity, which is good for moving heat from the stove exhaust to the pot, but also good for moving that heat to the outside air. "

Home depot sells empty paint cans in quart size. Used in this wood stove:

http://trailgear.org/

I just watched the steve house video and would like to bump this thread to see if anyone has any ideas on how to construct it?

I've got ti foil that I've used successfully for windscreens

thanks

mike

Just a note to folks working with titanium, use comercially pure titanium when using it in contact with high heat and/or flames.

Also, titanium is only a poor conductor of heat on paper. In actual use, titanium's ability to transfer heat improves, the hotter it gets.

The Ti foil at both Suluk-46, and TiGoat are CP.

Josh, in actual use titanium is still a poor conductor of heat, as compared to aluminum. It varies with the exact alloys compared, but its thermal conductivity is about a tenth of aluminum, regardless of temperature. Titanium does have good thermal resistivity, though.

–B.G.–

This was something I did back in April of 2004. The complete "How To" is located in a photo album at the "Make Gear" yahoo group. I think you might need to join to look at the photo albums.

http://groups.yahoo.com/group/MakeGear/

I thought I stared a thread for this here but can't find it.

I looked at the video and think his heat exchanger idea might be worth making a test model to play with.

Bob

Compared to aluminum, absolutey! Aluminum has much better heat transfer characteristics. People tend to look at a number in a reference book though, and say "oh that won't work", or "thats not good". Some of the numbers that you come across for Ti are based on electrcal resistence, which coralates well with metals like aluminum, but not with Ti. Ti is even used as heat shields in allot of aerospace applications, and this has to do with the temperature range where they are being used. Aluminum will oxidize at only a couple hundred degrees to the point that its heat transfer ability is severly inhibited, anodizing of the surface can help reduce this up to a certain tempurature though. Ti will begin to shine at these higher temps when oxidation becomes a bigger issue for aluminum. The oxide surface that is built on Ti at high temps does not inhibit heat transfer nearly as much as it does with other metals. Its all relative of course, but aluminum @ 1100 degrees, melts and then at a bit higher temp turns entirely to aluminum oxide with horrible heat transfer ability. Ti on the other hand will transfer far more heat @ the same 1100 degrees. Of course if you are in contact with a pot full of water at all times, you will never reach these temps, except at the extents of the heat exchanger, which could have a "building" effect. Like I said there would be other variables, it can be very dynamic depending on the particular situation. But for the same reasons that Ti is substituted for aluminum, like durability, I think there is good case for using Ti in such an application. Manufacturing alone would be one reason. Its not too often that Ti would be easier to work with compared to aluminum, but this would be one of those.

Josh, let me guess. Were you a liberal arts major?

–B.G.–

Bob,
Let me guess. You love to be pedantic?

Greg, I believe that Josh was the one who was attempting to teach.

–B.G.–

;-)

If you really get into titanium science, I recommend a book:
Skunk Works, by Ben R. Rich.

It is about the Lockheed Skunk Works developing the SR-71 spy plane that had a titanium skin, and partly what they had to go through to deal with titanium.

–B.G.–

You can build a heat exchanger into the pot. Here is a pic of my feeble attempt.

This shows about a 18-20% increase in bottom surface area. The same as a wider pot.

This goes along with improved heating, of course. This was designed for an alcohol setup, but can be adapted for melting snow.

http://www.youtube.com/watch?v=VerP7-aiEBw
This shows how to make a Caldera Cone. This can be used over your external WG or canister stove to support the pot. Used on the lowest setting, along with the above pot, this gives good efficiencies, also. Only the cone would be extra weight. But, this will also save fuel with an external stove, year round.

My thoughts only . . .
jdm

Bob

I have not read that particular book, but I'm familiar with the story. Yeah, if I ever decide to learn about titanium I'll read it :-)

Carlos

I have some .127mm Ti that I will send you, if you will cover the shipping. The stuff in the video looks to be some where in this range. Just let me know how big of a piece you want. Build the heat exchanger and report back, I'd like to see the results, and dont have the time for it myself.

Everyone else, I have a pair of goose feet for the person that makes a better guess than Bob's "Liberal arts major" which got some great laughs at my expense, though not imediately from me.

I'll take a crack at those Goosefeet- Electrical and Computer Engineering from Utah State. (ie You can't spell "geek" with out an EE).

http://www.titanium-brazing.com/products.html#3