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Don't understand using venturi burners


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I have had 3 or 4 forges at this point. One day I got really lucky and a guy had a forge for sale on Craigslist. It was a Ribbon burner. 

Right now you can build you forge body, line it, buy a Ribbon burner, fan, pipe,.....ect and have a complete forge for about $400.

My venturi forge had 2 burners, it was 12" long X 6" wide X 6" tall. It was costing me around $3.50 and hour....$30 a day.

  My currant forge is 18' long X 8" round with a flat bottom....it was made from a 12" piece of steel tube.  So it is much bigger then my old forge. I get a good 16" of even heat. The cost is a little over half. It runs me $1.68 an hour  So this saves me 50% on fuel. I am able to use it for forge welding, but have to crank it up to about 4-5 psi even then the cost is only about $2.25 and hour 

I know you can make a venturi forges cheap......but even if the average hobbie smith is smithing 3 days a month, they would save enough on fuel in 15 days or less to pay the additional cost of building a forced air ribbon burner. 

Should mention my results are based off using different forges for a few hundred hours of forging. So I have a pretty accurate result of fuel consumption. Another oddity... I found that the ribbon burner built by  Pineridge burners seem to be more  efficient then the ones I have built.... I don't know why but the guy has them dialed in and for $260 you can get a 4x10 burner. No... I don't have all the flow valve, safety, reset, pressurized, computer monitored emergency shut down call the fire department stuff on my forge. I have a 2nd shut of valve, 3 fire extinguishers, and I don't leave my forge unattended. 

Any way.... With money being such an issue I have a hard time with so many venturi forges being produced and talked about.

I have thought of only one use for a venturi burner. I wanted a forge only big enough for heating the end of a bar.....have been doing a lot on tenons and finials lately.

I am all ears tho.. and would like to hear what you guys have experienced personally. Not being rude but my results are very accurate and based on careful painstaking tracking of fuel use. I would fill my bottle every day and had a stop watch running, charted all my results over a 30 day period. So please give me solid feed back and not the "i had a buddy" "I heard of a guy"

Thanks

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Go to the Forge Supplies page at on my site and check out the Ribbon Burner attachment.  The first few pages are John Emmerling's plans for how to build a Ribbon Burner.  I haven't done all the studies and calculations that David has done but I do know that I get a more even heat, more control of the atmosphere in the forge and I do burn less fuel.  I run mine at about 1/2 psi and forge weld without flux.

Let me know how I can help you

 

Thank you,

 

Wayne

 

 

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Feel free to correct me if I'm wrong, but it sounds like you're asking why anyone would choose to run venturi burners rather than forced air ribbon burners.

So far I have only run naturally aspirated (what a lot of people refer to as venturi) and forced air single port burners.  My answer to that question would be the same for a forced air ribbon burner as well.  I'm currently running a single 1/2 inch Frosty T burner in my latest forge.  I haven't run through enough propane to give good consumption numbers, but I can tell you I'm using far less than I was in the previous forge with a 3/4 inch burner.  In that forge I was going through about a BBQ size propane tank every 10 hours or so, and even the gas station exchange rate would put me at about $2 US per hour for that setup.  As I've said though the current forge is more frugal with the propane, but I don't have good numbers to give you for it yet.

The other factors for me are simple.  I forge outside, but store the forge inside.  I don't like to have to run extension cords or long air lines and I'm not overly fond of the blower noise.  I can wheel my current setup anywhere I want and fire it up even if the power is out.  I did like the ability to easily tune the forced air burner to the desired atmosphere when I ran it, but I went back to NA burners for convenience and portability. 

It doesn't appear that you included the cost of the required blower or the small, but non-zero number for electricity to run your ribbon burner either.

Your current forge is much larger than mine, but it would appear that my propane costs with a single 1/2 inch burner are still less than yours with the ribbon burner. If we assume that forge construction costs are the same and we're just comparing burner and fuel cost I believe you are correct that the ribbon burner will win in the long run, but if you spend $260 + shipping for a burner and some more money for a blower, plus whatever pipes and fittings you need compared to the cost of a T burner, I think in my case at least it would be a LOT more than 15 forging days to make up the difference.

Having said all that, I have heard/seen only positive things from people who have used ribbon burners, and since the effectively slower flame speed allows more of the heat to stay in the forge for a longer time it's not surprising that they are more fuel efficient than NA burners.

FWIW, citing how much pressure you use in your setup doesn't tell us anything unless we know the size of the smallest opening/tube the gas goes through.  1 psi through a 1 inch diameter pipe is a LOT more volume per minute than 30 psi through a 0.023 MIG tip for instance.  Fortunately you did give us what we needed to know by telling us the relative costs between the two setups you were comparing.

Also, thanks for keeping track of that info and passing it on.  A ribbon burner forge is still on my list of things to do someday, but since I only get to forge on weekends, and not all of them at that, I'm trying to keep my building projects to a minimum in order to keep the forge time maximized.

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19 hours ago, Buzzkill said:

since the effectively slower flame speed

I'm confused by this. Why would the flame speed be any slower? Ribbon or not, burners generally run with the gas/air mix exit velocity at close to the flame propagation speed. No?

I'm also not clear why people believe ribbon burners will waste less heat. I'm not saying the do or don't (especially since I've never even seen a ribbon burner in person) but if I input X cfm of unburned gas/air it'll produce Y cfm of exhaust gas, and thus the same exhaust flow velocity regardless of wheather that input was via a single nozzle or a ribbon, right? So unless the ribbon burner is actually running at a lower cfm, I don't understand how the belief that the flame has longer time in the forge can be true.

I guess what it boils down to is if slowing the flame down to keep it in the forge longer works, then why would I not get the same effect turning down a regular burner? Every way I puzzle through this leaves me stymied - although the idea has some intuitive sense.

The more even heat distribution makes total sense. I wonder if people with ribbon burners run then at lower cfms because of the distribution alone?

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The short answer and please correct me if I'm wrong:  Venturi or gas jet ejectors = low volume/high pressure with a very small orifice for the gas metered in the neighborhood of .023-.035" that induces air in a mixing tube and has a singular outlet--depending on the number of burners installed.  RIbbon burners since they have multiple outlets need higher volume but don't rely on high pressure so the flame fronts in effect are spread out(less concentrated) resulting in a slower burn. 

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My large ribbon burner will flat out eat through some propane. The smaller ribbon burner does pretty good.  The larger on is a 33 hole and the smaller burner has 11 holes.  I'm building some Venturi burners to try out. A lot simpler and cheaper.

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3 hours ago, Andy98 said:

I input X cfm of unburned gas/air it'll produce Y cfm of exhaust gas, and thus the same exhaust flow velocity regardless of wheather that input was via a single nozzle or a ribbon, right? So unless the ribbon burner is actually running at a lower cfm, I don't understand how the belief that the flame has longer time in the forge can be true.

I'm certainly no expert on this topic, but let me try to explain it as I understand it and maybe someone with a deeper understanding can improve on my answer or fill in the gaps.

In many cases gases behave similarly to fluids, so I'll try to explain it that way.  If you were shooting a single high pressure stream of water into a forge sized container at the orientation in which we normally aim our NA burners it would be somewhat violent and you'd get a lot of splashing out the openings.  In our case the splashing can end up as excessive dragon's breath, which amounts to fuel burning at the openings instead of inside the forge where we want it.

In the second case if instead of a single stream of water you divided the same volume at the same pressure into around 20 smaller streams whose combined area was 3 to 5 times the area of the single stream, you'd still end up with the same total amount of water leaving the forge, but it would not be as forceful and on average the water would spend a little more time in the forge. It would be running out more than shooting out. By increasing the area of input into the forge, you decrease the pressure at which it enters the forge.  The total amount of exhaust gases per unit of gas/air mixture is the same, but it's not being pushed out as fast/hard by the incoming fuel and air.

I believe there is also a difference in combustion between the two.  The bigger the burner, the greater distance needed for complete combustion.  If the flame hits whatever is opposite of the burner port before combustion is complete then it will be cooler.  I've seen this in a few instances where a darker spot was visible directly opposite the burner when turned up to a certain point.  IIRC there was a post on here a while back which referred to this as well. It mentioned that some forges tested actually ran hotter at lower psi than they did past a certain point if my memory hasn't failed me.  There may also be some combustion benefit with all the small ports in close proximity with each other, but that's nothing more than a guess on my part.

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18 hours ago, Buzzkill said:

In our case the splashing can end up as excessive dragon's breath, which amounts to fuel burning at the openings instead of inside the forge where we want it.

Is it your belief that the dragon's breath is caused by gas that didn't have enough time to burn in the forge?

I always assumed it was completely caused by fuel that didn't have enough oxygen inside the forge, and thus burned on exit into the atmosphere.

On 5/14/2017 at 0:12 AM, Buzzkill said:

believe there is also a difference in combustion between the two.  The bigger the burner, the greater distance needed for complete combustion.  If the flame hits whatever is opposite of the burner port before combustion is complete then it will be cooler

I think this is the real reason. If you think of the "surface area" of the flame itself, lots of little flames will have more surface area than one big jet. So I think the gas at the centre of a small jet will both slow down more quickly, and heat up faster, thus burn sooner. Total guess. If your belief about dragon's breath being related to time is true, then this would be the second part that makes it make sense (to me at least).

Your other points about pressure and exhaust exit velocity I'm not sold on, for reasons that would take lots of paragraphs of tedious explanations that would just annoy people reading (but if you're interested I'm happy to go on and on and on about it).

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I would be much more interested in hearing about your stats from the same forge with a different burner.

I have switched from blown burners to Venturi burners a few years ago, I find them better and simpler to use. The company who makes the burners (Amal) has a gas air mixer made for ribbon burners, I have one but have not devoted the time to playing with it yet or figuring out the burner.

 

I am always interested in saving money,( it's not unusual for me to have 5 forges running at the same time here)  but find convenience/ease of use to be my priority .

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On 5/13/2017 at 9:03 PM, ede said:

RIbbon burners since they have multiple outlets need higher volume but don't rely on high pressure so the flame fronts in effect are spread out(less concentrated)

Hi - In both cases the burners are required to operate with the gas/air velocity at the nozzle exit being at least the flame propagation speed. That means that a single-large-burner running at the minimum will have the gas/air exiting at the same total (stagnation) pressure as the many-small-nozzles also operating at it's minimum.

The fact that the small nozzles are diffusing the flame is probably important.

It's also possible that the many-small-nozzles allow ribbon burners to run closer to their minimum? For all I know my burner is dumping fuel/air into the forge at several times faster than the flame propagation speed.

Playing this thought out: On surface area a ribbon burner with 26 x 5/16" ports is like a 1.6" single port burner (26x5/16=2sqin, which is the same as a 1.8" diameter circle).

Most people don't have 1.8" diameter burners, they have 1" or 3/4". 

The real world will be more complicated than this, but if a ribbon burner was running at the minimum then a 1" burner would have to run at 2.5x faster flow rate to push the same amount of fuel/air. So that seems like it would mean the single larger burner will have a lot of cool, unburned gas in the forge, and it would make sense that would be bad.

 

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On 5/15/2017 at 7:55 AM, Andy98 said:

The real world will be more complicated than this, but if a ribbon burner was running at the minimum then a 1" burner would have to run at 2.5x faster flow rate to push the same amount of fuel/air. So that seems like it would mean the single larger burner will have a lot of cool, unburned gas in the forge, and it would make sense that would be bad.

There are a lot of variables that come into play here, and I certainly don't have a good enough understanding to mathematically explain everything that is going on.  However, I look at it from the opposite point of view.  As you said most single port burners for the size of forges we deal with are 3/4 inch to 1 inch in diameter. Using your example of 26 ports at 5/16 inch diameter each, that's about 4.5 times more area for the ribbon burner than a single port 3/4 inch diameter burner, and a little over 2.5 times as much area as a single port 1 inch diameter burner.  If you assume the same volume and pressure of gas/air introduced to the ribbon burner by a 3/4 inch or 1 inch pipe then yes, the combined pressure of all the the smaller ports will equal the pressure that would have been in the single port burner (we'll ignore the additional friction and back pressure for this purpose).  However, the pressure at each port is significantly reduced because of the additional total area. As long as the pressure per port is enough to produce a gas/air mixture speed at or above the flame propagation speed then the burner will function.   It's worth noting that for single port NA burners it's likely that we are far above the flame propagation speed most of the time.  It's fairly easy to get a flameout by turning the pressure up before the forge is hot with a lot of burners.  Once the forge is hot this becomes largely irrelevant since the temperature inside the forge is well above the flash point for the gas/air mixture, making a flameout darn near impossible even if the fuel/air speed is many times the flame propagation speed.

The bottom line for me is this: whether I can produce accurate math to explain the activity or not, the reported experience from many people on here is that ribbon burners get very hot and tend to use less fuel to do so than single port NA burners in the same forge.  I like to know how and why things are the way they are too, but I'm also willing to accept (at some level) the word of people with experience over my armchair musings and crude attempts to produce the mathematics to support the claims. I wish I had the time and money to experiment and record my results, but I don't right now.  It does make sense to me that a lot of smaller "softer" hot flames will be more beneficial in a forge than a single big "harder" flame though.

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Andy: Put down the calculator and do some experiments. You are finding differences that don't matter. I did a lot of the nozzle area math when I started playing with the idea of a NA ribbon burner and they don't really apply, not in the sense you THINK.

Flame velocity is incredibly important to furnace function. I'm having trouble believing you actually think gas burning OUTSIDE the forge isn't a factor in efficiency, effectiveness and economy.

The lower the flame velocity the longer the flame stays IN the furnace and hence transfers heat to the liner.

If you actually know as much about fluidics and combustion as you wish to appear, I'd be thinking unkind thoughts about your arguments. I'll give you the benefit of the doubt and assume you're just a kid instead.

***************************

Ede: No, a ribbon doesn't NEED higher volume or pressure than a single outlet burner. It needs a balance of outlet capacity vs. air fuel supply. Get it right and they're so stable it can get you in trouble but that's just operator error, not an equipment flaw.

The ONLY reason I played with and developed a multiple outlet burner that would work with a T "burner" inducer is I couldn't believe how much pressure the gun (blown) designs were calling for. Low and BEHOLD multiple outlet burners don't need as much pressure as a wimpy NA inducer produces. I just unscrewed the thread protector from a burner I was using and screwed it into the plenum for a ribbon burner and it's decievingly stable. It can fool you into turning psi down so low there isn't enough air fuel mix flowing to keep the burner block cool, so after a couple hours running at about 3/4 psi the ribbon block heated up enough to burn back. The silly thing is stable as a can be running between pegged at0 psi on my gauge to pegged at 20psi. The max range of my old regulator.

Run at 2-3psi it ran for 6 hrs, yellow heat in a forge with ID 18" x 9" x 5" with zero issues.

Any, ANY burner that has the flame jumping off the end before it begins burning has too high a fuel air velocity at the outlet: single, multiple or shaped. This is true of ANY kind of burner.

Frosty The Lucky.

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Wayne, Buzzkill and Frosty  I see I have argued and speculated you all past your tolerance levels (not to mention having hijacked the thread). 

I do totally accept the stated benefits of ribbon burners and although I see that my first post here does read a lot like I was rejecting that information. It does also make intuitive sense to me - at least I did say that somewhere above.

...but I do also want to understand the mechanics of why they are better. I don't see that as a bad thing, and I don't apologize for that. I realize that some people find theoretical discussions annoying, and I do apologize for being annoying. 

Frosty: I think combustion is voodoo. I don't think I have the vaguest idea of how it works. I do think I have my fluids right (although I'm less sure I have expressed them clearly) but would welcome being told if and where I've gone wrong so I can get it right next time. I'm not surprised burning outside the forge is wasteful, but I am surprised mixed gas/air could get all the way to a forge exit before burning completely (I thought it must mean there wasn't enough oxygen in the forge).

I would love to experiment more but I have family commitments that prevent that.

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Actually YOU are arguing with people who have presented empiricle proof they know what they're talking about. We've also explained the what's and whys of the devices in as simple language as we can manage. Well, I have but I know what's going on and why. You seem to be stuck on finding differences without distinction. Yes we get tired of this behavior, tired enough to tell you so.

1, Go to the bathroom, stand in front of the mirror and say, "I think combustion is voodoo. I don't think I have the vaguest idea of how it works," out loud to yourself a few times and see if you don't feel like you shouldn't have opened your mouth in this discussion.

2, You aren't arguing "theory" it doesn't even meet the criteria to be a hypothesis. You're expounding on what makes sense to YOU. See point 1.

3, There is flame outside the furnace, that's unburned fuel OUTSIDE of the furnace it's unrealized heat and wasted money.  Before you say ANYTHING about fuel and air see point 1 and YOUR quote.

4, If you don't understand how going too fast can mess up your voodoo I can't help you, I'm not going to explain it again. And no you don't even have a working handle on fluidics.

You haven't read Dunning and Kellog have you?

Frosty The Lucky.

 

 

 

 

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Andy,

The mechanics of ribbon burners are simple: Generally--but not always--fast flames are the hottest flames. Unfortunately those hot flames also tend to transit the heating chamber of a forge or furnace equally fast, making an inefficient waste of useful energy. So the trick becomes how to break the super-heated by products of those fast hot flames around longer by breaking down their breakneck speed. Fortunately, even fast flames, and their by products, are only gas. Gas doesn't have much mass. A large single flame traveling at a relatively high velocity, will transit the forge way too fast, and so we aim the burner on a tangent, to make the flame path a spiral, increasing the distance it most traver to reach the exhaust opening; this helps a lot with efficiency.

Having created the longest possible distance for the gases to slow down over, what remains to help "put on the brakes"? Well we know that gas doesn't have much mass, so it shouldn't take much to slow it down, right? A single large flame can bowl the thin atmosphere in the forge out of its way FAR easier than several small flames can; this is why I recommend that people with very small forges mount two smaller burners, instead of a single larger burner; three is even smaller burners would be even more efficient, and so on and so forth. What is a ribbon burner but very many very small burners? Get it good buddy?

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On ‎5‎/‎15‎/‎2017 at 8:55 AM, Andy98 said:

Playing this thought out: On surface area a ribbon burner with 26 x 5/16" ports is like a 1.6" single port burner (26x5/16=2sqin, which is the same as a 1.8" diameter circle).

The real world will be more complicated than this

Yes the real world is more complicated than this, mostly because of friction and boundary effects inside these nozzles and at their exit.  The boundary layer adjacent to the walls of a pipe can have a very significant effect on how much fluid flows through that pipe as well as the local velocity of the jet at the exit  (many smaller pipes is not directly equal to one larger one as regards fluid flow given the same upstream pressure). 

You didn't think the gas/air mixture inside the burner was flowing at a constant velocity at each crossection did you? 

This doesn't even include issues with turbulent verses laminar flow (note I'm not saying that the mixture flow inside the pipe is either, haven't done the Reynold's number calcs. but it does make a significant difference)  and the end effects of a jet exiting the orifice itself.  Personally I think that the turbulating end effects may be a big part of why the ribbon burners slow the flow down so abruptly and consequently work well, but I haven't done any of the analysis, so that is just speculation.

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Thanks Latticino, right wrong or indifferent your speculations on burners are always worth reading and thinking about. Just laying out some of the rest of the variables is thought provoking. To add a bit from my experiments of yore.

Velocity in the tube isn't consistend across the cross section at any point in the tube. The center of the stream moves faster. This is indicated by many burners, the flame being roughly conical.

Nor is it "either" laminar or turbulent flow. If there wasn't SOME turbulence the fuel and air wouldn't mix. Too much turbulence and the burner loses induction. Against the inside of the tube the flow  develops a laminar flow. (Bernoulli says so and I believe him, it sure looked that way blowing smoke through a clear plastic tube in the day I was trying to "understand" the things.)

In the center of the flow or I should say, away from the walls the flow becomes more turbulent, moving faster and MORE turbulent the closer to the center you look. I made a couple inducers from clear lastic tubing and blew smoke through the jet to observe what was going on. I stopped doing math at the 1:12 (or 12%) taper to control bad turbulence and skin friction more math didn't help.

The 1:12 rule of thumb does NOT apply in multiple outlet burners.

I stopped even trying to "understand" or even accurately describe what the flow is doing in a burner. While I'm interested I really only need the things to work properly and I can make that happen using basic knowledge, observation and experimentation.

Frosty The Lucky.

 

 

 

 

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Well yes,  if we use something that creates a flame nozzle (in effect) we will slow the flame velocity down more than a simple orifice does; this is shown quite plainly in the difference between the industrial version of ribbon burners and homemade ones. I am all for getting the maximum out of any tool, but as Frosty has shown me, good enough is usually good enough...of course, I'm glad to go overboard, if encouraged to. Multiple steel tubes within the burner block, silver brazed into the mixing chamber; yum, yum! :)

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I looked at the steel outlets brazed to a plate in the plenum too and even thought about doing that. I think it has two things going for it:

1, The steel tubes are slicker than refractory for a lot less friction. 

2. Steel tubing brazed to a plate increases the air fuel contact and decreases contact with the cast refractory block so there's less heat transfer keeping the mix cooler.

Less friction means you can use a slower flow and still keep it cool enough to not burn back.

Oh just thought of a, 3. steel tubing would act as rebar making the refractory stronger so you could use a much higher % of evacuated bubbles in it.

Frosty The Lucky.

 

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I think what Mikey is referring to on the purpose of the tubing in ribbon burners being stepped orifices is discussed in a 2009 thread.  And I quote:

"Brad, 

Nice job on the burner! You have put a lot of thought into it. In the past I have built several IFB (Insulating Fire Brick) burners. Even the G28's don't have the lifespan of a burner block cast from a high quality refractory, but since your design makes it so easy to replace that becomes much less of a factor. 
A tapered hole won't have much effect. What will help with flame retention and stability is a stepped diameter orifice like I use. The first part of the orifice is smaller in diameter. This is the metering orifice and it supplies a consistant amount of fuel mix at a relatively high speed. The second larger diameter part is the delivery orifice. Here the fuel mix expands and slows down just before leaves the burner. This helps the flame retain on the block face, and gives better flame stability over a wider turn up/turn down ratio. The trick, of course, is in balancing the relationship between both the lengths and the diameters of the two orifices. Whether or not you could get it done in the thickness of an IFB I'm not sure, but bit might be worth fooling with.

Charlotte,

"a little leak might not make any real difference" unless it leaks out into and behind the fiber blanket forge wall. Being a manufacturer I tend to see design in terms of liability. You will have to forgive me, it comes with the territory :grin:

Regards, Tom
"

 

 

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Pine Ridge presses there tubing in.  

If they were hard silver brazed into place, the baffle plate would have to get really hot to heat up the solder.  Hard silver solder has a solidus temperature of 1365 ℉.  That equivalent heat in metal color would be a dull red.  The liquidus temperature is 1450 ℉.

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9 hours ago, Frosty said:

Oh just thought of a, 3. steel tubing would act as rebar making the refractory stronger so you could use a much higher % of evacuated bubbles in it.

I've thought about this as well, but was wondering about the different rates of thermal expansion between the tubes and the refractory and the potential for cracking.  Then I wondered about using a couple layers of rigidized kaowool around the tubes instead of castable refractory.  I really wish I had the time and money to try these things out.

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It is good to hold both sides of the coin in view. Ease of construction cannot be ignored, if we hope to have many people build ribbon burners. On the other hand, these tubes have everything to do with best burner performance. If we don't just give up, one of us is likely to come up with a way to have our cake and eat it too :)

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David,

So, anyway there are two good answers to your question:

(1) I have seen many people in love with their gas forges, and just as many who hate theirs. Neither group necessarily knows beans about either their forges or its burners. The deciding question never ends up being what kind of forge or burner someone has, but how well it was built. A properly constructed naturally aspirated burner will out perform a poorly built fan-blown burner, and visa versa. Ribbon burners--even homemade ones--have great heating potential from less fuel, because many small flames can slow down much faster than a single large flame. Even multiple miniature  naturally aspirated burners can't do as good a job of slowing super-heated gas down from a fast flame; this is obvious on the face of it. On the other hand, the law of diminishing returns will even out the difference equally fast! They ain't no such animal as a perfect burner; ditto for perfect forges.

(2) Jewelry stores show hundreds of pieces for sale, rather than just two or free "perfect" items, because people want CHOICES. So one mans 'perfect' burner is another man's junk. Junk isn't necessarily something bad. But, like weeds, may simply be unwanted. So, if I was making a miniature forge in a helium cylinder the smallest ribbon burner anyone can make would be monstrously oversize in return for very minor fuel efficiency. At this point I could ask why would anyone want a clunky ribbon burner, when their are hot little NA burners in the world...and be just as wrong as I could be, in your view :) 

Dang. but this has proved to be a good thread!

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