Burners 101

[deepwater]

5 minutes ago, Panik said:

By all means run with it...

Great, thank you! 

[Panik]

Mikey - One of the reasons why I've asked a couple questions about the quality of the flame I have managed to produce is because I have a curiosity about the how and why of fluid dynamics (is that the right choice of words here?) and how it impacts the flame a burner produces.

To that end, I dug through this forum and located a couple of posts from you discussing the why behind the book you wrote and its intended audience. In stating that, I wanted to say thank you for authoring that book.... both because I am getting ready to ready to read a copy I downloaded and because I remember what it was like to be a curious college student without a great deal of resources. I still am very curious, if imperfect student.....just with a bit more resources

Rather than muck up this forum with a bunch of questions that have been asked and answered multiple times I'm going to continue digging through the forum and hopefully ask the occasional, more informed, question However, I would like to further supplement my reading. Does anyone have any additional book Edit-(or other accessible publication) recommendations on the subject that they think would be somewhat accessible to someone who doesn't have a highly technical back ground?

[Mikey98118]

10 hours ago, Panik said:

One of the reasons why I've asked a couple questions about the quality of the flame I have managed to produce is because I have a curiosity about the how and why of fluid dynamics (is that the right choice of words here?) and how it impacts the flame a burner produces.

Yes, fluid dynamics are one of several forces, which affect gas flames. Unfortunately, burners and torches are profit producing equipment. Therefore, the reader won't get very far beyond beginning principles, before the very people who could give insight into them have no reason to cooperate. And those, like instructors, who have every reason to help, tend to be clueless.

[Alphafarrier]

On the note of fluid dynamics, I have a question about the bevels at the fore and aft end of the slots on a Mikey burner. 

Is there an ideal angle?  Or simply the lowest angle possible?

Is there an angle that is "too steep", or is some better than none?

[Mikey98118]

Heat output of different burner sizes

Frosty said:

As a general rule of thumb the output of a forge burner is a function of the square of it's mixing tube diameter. Meaning a 1" burner output is 2x that of a 3/4" burner. A 1/2" burner is 1/2 the output of a 3/4" burner.

Fuel consumption is on the same curve. A 1/2" burner uses 1/2 the propane of a 3/4" burner, and a 1" uses 2x as much propane. 

This is for the same type burner of course, do NOT think the output or fuel consumption ratio applies between different types or even styles. For example a 3/4" linear and a 3/4" T use different amounts of fuel and put out different BTU/second rates. Yes?

Different burner designs will combust fuel at different rates, to produce differing amounts and types of forge atmospheres. So this very helpful "yardstick" must be viewed with the limits of its application in mind; which doesn't mean that the yardstick is faulty; it means you must apply it with common sense. Therefore, to have a clue how much output any given burner can provide, you must start with a known design, and compute its BTU potential, at a given maximum rate at which its flame either becomes unstable, or else begins to degrade in quality. Then find the minimum output that provides a stable flame. Thereafter, you can feel confident that other burners of that design, if running properly, can be measured.

Are you done yet? NO; different flames, from different burner designs, will create very different performances in, differing forge designs. Their is accurate no comparison, between the performance with a high speed Mikey burner, and the softer flame of a "T"; the former may be more desirable in a tunnel forge, while the later is superior in most box forges. This doesn't even scratch the subject of multiple flame burners. So...remember that every yardstick has limited application.

1 hour ago, Alphafarrier said:

On the note of fluid dynamics, I have a question about the bevels at the fore and aft end of the slots on a Mikey burner. 

Is there an ideal angle?  Or simply the lowest angle possible?

Is there an angle that is "too steep", or is some better than none?

Ideally, the steeper the angle the better. In practical terms, anything beyond sixty degrees is a complete waste of time.

[Alphafarrier]

Ok, so a 45 degree bevel, while not ideal, should work OK?

[Mikey98118]

Yup; I'm inclined to hold out for sixty degrees, but maybe that's compulsive behavior. In any case, nothing stops you from "improving" the burner if the same madness overcomes you 

Look; burners are kind of like race horses; some just run faster than others. If your horse comes in slow, then its time to try harder

[Alphafarrier]

That's a great analogy, especially for me   I'll see how it runs, and adjust from there.

[Fishgod]

I know I'm not the sharpest knife in the block but I'm just trying to make sure I understand "Burner, Forge Design, Fuel".  I see a ton of what I believe are misconceptions and or flat our wrong statements on the internet. There are a bunch of statements that forced air burners "ribbon or standard" use way less gas as compaired to venturi burners.  The only way that would be correct is that the forced air burner is better tuned than the venturi burner. Propane only produces X amount of BTU's per X volume of gas. 

1. The forge design and burner have to be thought of as one.  So burner A may bring forge A up to working temp but burner A may not do the same thing in forge B.  Even though the forges have the same internal volume.

2. Burner A "Venturi with .035 mig tip" properly tuned will produce X btu's for X amount of propane.  Burner B "Forced Air with .125  Venturi" properly tuned will produce X btu's for X amount of propane even though it is running at a lower PSI.  Wouldn't both burns have to burn the same amount of propane to produce the same BTU's? 

[Another FrankenBurner]

Good points.

As you stated, powered vs atmospheric burners would depend on burner efficiency.  By efficiency here, I mean what percent of the available btu's in the provided volume of fuel is actually being liberated in the flame (and how much happens inside the forge).  Provided both burners are burning the fuel with the same efficiency, yes, same amount of fuel, same amount of energy.  

The biggest problem I see with blown ribbon burners is their tuning/construction.  You don't have to build carefully to get the amount of air you need so they are often built with no regard to throughput.  Some believe you "need" a high pressure blower to make them work.  Frosty's NARB work should have put that misconception to sleep.  You only need high pressure if you've restricted the flow path.  The flip side, sometimes the burner blocks are so wide open that the stream has to be forced to a high volume to maintain a flame.  Ever seen a picture of a ribbon burner forge with 3 feet of dragons breath.  

Just like with atmospheric burners, powered burners can be built fuel efficient or not.  There is a lot to be balanced.  Both have their application and neither should be disregarded.

[Frosty]

Okay, once again. Stop believing what you see on youtube, the vast majority are wrong some dangerously so. Propane has X BTUs per a given volume though it is not a precise number but it's a  reasonably narrow range, maybe 50+/- BTUs. 

Shape has as much effect on a forge's relationship to burner and temp. A long narrow 300 cu/in forge won't heat evenly with a single 3/4 burner, it'll want two 1/2" burners or four 3/8" burners. Another major factor is how open the forge is, one with wide open ends will spend most of it's fuel heating the room. Neither can be closed down completely though, there MUST be sufficient exhaust or it dies. Just like you and I. 

As AFB just posted it doesn't matter, gun (blown) or NA (Naturally Aspirated) properly tuned delivers the same BTUs per given volume and the same absolute flame temperature.

I don't have a dog in the Gun vs NA burner debate, both have places where they're the superior choice but all things equal they do exactly the same thing for the same fuel bill.

Frosty The Lucky.

[Fishgod]

Frosty,

I'm not believing youtube and facebook.  I see posts/videos and because of this site I say to myself that not right or that's a scary design.  I wanted to make sure my limited knowledge was correct from what I have absorbed from this forum. 

[Mikey98118]

3 hours ago, Fishgod said:

2. Burner A "Venturi with .035 mig tip" properly tuned will produce X btu's for X amount of propane.  Burner B "Forced Air with .125  Venturi" properly tuned will produce X btu's for X amount of propane even though it is running at a lower PSI.  Wouldn't both burns have to burn the same amount of propane to produce the same BTU's? 

Actually, this is only part of the equation. If burner"A" combusts all of its fuel within the forge, but burner "B" doesn't, than a BTU chart isn't going to provide an accurate picture.

If burner"A" combusts all of its fuel within the in a very short flame, but burner "B" doesn't,  then more if the first burner's heat will have time to transfer into the forge interior.

Thus, a properly tuned multi flame burner, is going to have added advantage, if it is place in the right forge design for its best use.

[G-son]

Then there's the flame temperature. Different burners seem to have different temperature flames, and logic suggests that the burner can not heat a forge above the flame temperature, no matter how big the energy output is.

[Mikey98118]

Yes, but "here's the rub"; the rated flame temperatures of various fuels, depend on flame speed. Flame speed of some fuels can't be fiddled with much; This doesn't hold for LPG fuels. Adiabatic flame temperature of any given fuel has a set mathematically derived limit.; that ceiling is approximately 3600 F for an air/propane flame. If you look this fuel up on a BTU chart, it's rated way lower. If you look at the ratings for air/propane torches today, they are two to four hundred degrees higher than a few years back; this is because of design improvements in the torches, creating way harder flames.

[Frosty]

I need another term clarification Mike. When you say temps depend on  "flame speed". Is that the "rate of propagation" or a use I'm not aware of? 

Frosty The Lucky.

[Mikey98118]

Flame speed is the rate of propagation. The term probably (I wasn't there) originated with timed tests of flames down a tube (length of hose) that were used to note flame speeds on the first charts. Some fuels create very fast flames (ex. hydrogen and acetylene), which can seldom be improved. LPG fuels have low velocity flames, comparably; they can be tinkered with quite a bit

[Frosty]

That's what I was thinking it meant.

Thanks.

Frosty The Lucky.

[Mikey98118]

    Engaging vortical flow

Vortex is a term from the study of fluid dynamics, describing a region in which the fluid flow (gas, liquid, or plasma) revolves around an axis line.  The vortices generated on the tailing edge of a plane’s wing only generate drag. At the other extreme, a tornado’s funnel has terrible destructive power. A bathtub drain effectively employs  vortical flow to good purpose.

    There are numerous ways to swirl incoming air and fuel gas, but only when the mixture passes through a restriction (ex. pipe reducer or funnel) can vortical movement become a practical engine. Any device that creates spin at the air entrance will increase vortical flow; this includes directly opposite openings on “T” plumbing fixtures, or blade structures in front of an air opening, etc. But, forcing air directly into a funnel entrance increases vortical flow at the cost of increased flow pressure.

    The impeller blades on computer fans, can be employed to power up a passive vortex, by predominantly creating lateral spin—not forward push—at the funnel entrance; thus, its energy is spent directly strengthening vortical flow. Vortical flow does not increase overall flow pressure. Set flat ether flat fan blades, or impeller blades in front of an air opening, and incoming air will be swerved in its path, creating swirl. But spin the blades before an opening, and the flat blades will create push, while the impeller blades simply create more swirl.       

    That appears counter intuitive. How can a spinning fan avoid creating air pressure? By flinging incoming air outward, from impeller blades, toward the inside of the funnel wall, where the increased pressure creates vortical movement. Meanwhile, air pressure throughout the rest of that area’s cross section becomes a partial vacuum (a low pressure area), offsetting the pressure increase near the wall, similar to that in a tornado’s funnel cloud. During vortical flow, the incoming gas/air mixture’s forward velocity and spin rates are increasing, all the way through the burner’s funnel section, while flow pressure doesn’t change appreciably. This high speed mixture flow swirls through the mixing tube; when it expands into the burner’s flame retention nozzle, another low pressure flow is produced, behind the flame.

    A flame envelope, is essentially a controlled explosion; it creates a weak outward force. But the push of a gas flame isn’t equal in all directions. The gas/air mixture is being flung forward, so there is a little more shove away from the burner’s end, than in any other direction. All things being equal, the harder the flame is tuned the faster the gas/air mixture will rush forward, and the greater that imbalance grows. At some point, the out flung mixture will force the flame far enough from the ignition source to snuff it.

    Atmospheric pressure is a constant force all around the flame envelope.  But,  create a low pressure area at the burner’s exit (by use of a flame retention nozzle), and atmospheric pressure will press the flame harder against that nozzle, than in all other directions; the difference isn’t much, but it is enough to allow much harder flames to be maintained, because the kinetic force of the air and gas molecules is also minimal.       

    But, doesn’t the gas stream produce positive pressure in the burner? Of course it does. Positive pressure in the mixing tube is needed; otherwise the burner flame would back-fire into it. The trick is to increase the mixture’s feed rate (speed) without a pressure build up, by only increasing the speed of incoming air flow, without adding flow pressure.

    In summery; excess positive pressure in the burner’s gas/air mixture severely restricts possible flame intensity. So powering up vortical flow, instead of pushing air forward, allows stronger flames than are possible in either forced-air, or naturally aspirated burners.

Do we all need to rush out and buy computer fans for our burners? NO! The point of this discussion is to pay more attention to vortical motion in burner designs, so that improvements are made deliberately, rather than as happy accidents.

[Trevor84]

I had a little breakthrough yesterday when I was tinkering.

Now this may be documented already but I found that you can cut threads on the outside of the 1/8" sch 80 nipple using a 7/16" 20nf I think it was. Also you can drill and tap the 1/8" fittings with the 7/16 20nf this way you don't need set screws you can screw in and out to tune as long as you got everything straight. And in some designs like a Mikey, Oliver, straight straight tube burner you may be able to stream line a bit with let's say the 3/4" steel, straight sided coupler/thread protector then a 3/4"-1/8" bushing tapped for 7/16" nf..... May be a scooch more streamlined without having to turn/grind anything down.......

In this case I tapped the T and I was able to clamp the 1/8" nipple in the vise and just screw the burner up and down. However there's not much meat in the wall of the T so I may tap the T for a bushing then tap it then and also use a jam nut to lock in the orifice depth once I find the sweet spot.

This is temporary flare for now, it's a bit larger than the 1:12 so it holds the flame a bit too deep. 

This burner as is currently:

1/8" nipple

0.030 contact tip

1",3/4",1" T

3/4"x7" mixing tube

Flared out to 1 1/2" with a 1 3/4" over hang. 

This is still in the testing phase, I already know that some of my ratios are random in this build but I was just tinkering and had limited fittings (need to hit up the plumbing store) 

I'll update in a few days when I get a chance to get back in the shop and take a few progress pics. 

 

Thanks for copying the vorticle flow write up forward Mike it makes it nice and easy to find...... You have it explained in a way that's fairly easy to visualize. 

[Frosty]

If you use a lock nut the jet won't wiggle in the T. Just snug it when the jets where you want it if you put too much torque on the wrench you'll strip the threads in the T.

Flame looks pretty good but that'll change when you put it in the forge.

Frosty The Lucky.

[Trevor84]

Thanks, in the forge tests will be coming in a couple days 

This is hard to describe but I'm wondering if there is a type of adjustable nut thingy that could be fixed to the T but have a nut that turns freely so that the burner and the jet can stay stationary but turning the nut would just adjust the jet in and out. 

I think I've seen something like that before but can't think of where or what it would be called......?

Any ideas, does that make sense? 

 

I guess kinda like the screw in a crescent wrench but a female version... 

[Mikey98118]

hand flaring a burner flame retention nozzle is always tricky. But here is a gentle hint; when it comes to how much to increase the diameter on the flare, start with 1/8" and larger, and increase the flare diameter by an additional 1/16" at a time, until the out rushing flame no longer touches the inside of the nozzle, for maximum effect.

[Trevor84]

Thanks Mike, I'm going to go back and try a couple more going slower

When you make a "step nozzle" for a 3/4" burner do you use sch 40 or sch 80 for the 1 1/4" nozzle portion?

I'm finding the 1 1/4" sch 40 nipples are almost 1 1/2" ID so real sloppy over the 1" spacer and I'm getting too much pressure drop. 

[Mikey98118]

I used schedule #40 stainless steel pipe and stainless steel tubing that were as close as possible to it, in sizes that weren't available in pipe at the time. Such sizes don't mach up perfectly inside each other. Some parts were ground to fit, and others were slight so that they could spring open, to fit.