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Burners 101


Mikey98118

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5 minutes ago, John in Oly, WA said:

I'll see what I can do, but it wouldn't be a "how to" video. More like a "how I'm figuring out how I do". I have some 'round about, unorthodox ways of constructing things sometimes.

It wouldn't need to be a "How To" but the process itself would be fascinating and maybe give some of us fence sitting wannabes the drive to build their own!

 

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1 hour ago, John in Oly, WA said:

I'll pick up some of the La-Co flux. I think I have some tin/silver solder around. Then I'll be needing capillary tube.

I'm far from certain that you will need anything beyond MIG tips. Yes, I've said repeatedly that the smallest contact tips are just a little too large for a 1/2" Mikey burner, and that a 028" gas hole would be better, but let 's not forget that incoming air is fan assisted on these burners. For the same reason the 3/4" burner will probably need a .030" at a minimum

1 hour ago, John in Oly, WA said:

I'll see what I can do, but it wouldn't be a "how to" video. More like a "how I'm figuring out how I do". I have some 'round about, unorthodox ways of constructing things sometimes.

Please make it as close to a how-to video as you can. The more information available on this burner the better. I know authors are supposed to hoard information on their subjects, but this is a new day; the old rules simply don't apply.

You need to query me about every concern you run across; think of yourselves as helping out all the people who are too shy to speak up. We are all writing for a large crowd :D

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1 hour ago, Mikey98118 said:

the 3/4" burner will probably need a .030" at a minimum

I have .030" and .025", .035", .040", .045".

Oh, I'll be asking you a lot of questions Mikey, I'm sure.   You're the expert, I'm just trying to follow along.

One thing that will come up is how far in to position the MIG tip in the funnel.

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On 2/15/2018 at 1:48 PM, Mikey98118 said:

a little longer than the inside diameter of the mixing tube--so far. But flame nozzle length also depends on how long the spacer ring is. I have found an extra 1/4" beyond the size of the mixing tube's inside diameter to allow all the leeway needed to tune a burner, add to that a minimum of 3/4" for the spacer ring, and you have a good minimum length for most flame nozzles.

Well, I'll have an idea how to build one at the end of this process, but for expert I'd need to understand the theory behind it all. We'll see.

At any rate, my understanding before I start cutting pieces - 3:1 maximum ratio between fan opening diameter on the funnel and mixing tube diameter, 14:1 ratio between the length and the inside diameter of the mixing tube, and nozzle minimum length = I.D. of the mixing tube + 1/4" + 3/4". And don't permanently attach mixing tube to funnel, so they can be separated for tuning and cleaning.

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39 minutes ago, John in Oly, WA said:

And don't permanently attach mixing tube to funnel, so they can be separated for tuning and cleaning.

This is not a rule, but a preference; The difference being that, if there is a good reason to permanently attach the mixing tube to a reducer fitting, then a long centering rod allows that to work out okay, although reducer and mixing tube must then be aligned perfectly before brazing or welding the joint; afterward, its inner surface must be power sanded to ensure good airflow; this aggravation becomes an actual impediment to progress when funnels are used as air scoops.

As for theory; I will cut and past it shortly.

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Introduction to Vortex Burners

Craftsmen have constructed forced-air gas burners for decades; typically employing squirrel cage blowers. But powering air swirl, instead of air push at a burner’s air intake radically changes output performance. Why? Because the more forceful the output of a burner is the more its output must somehow be broken back in the flame nozzle, to keep the flame from being blown clear off the burner’s end; that’s pretty counterproductive. While flame nozzles can be used to ease the problem, reducing the problem at its source gives far better control. Unfortunately, the idea of pushing input air is so entrenched that the other popular terms for powered burners are “forced-air, and fan-blown” Standard forced-air burners still have a place, notably on multi-flame burner heads, but are awkward on compact heating equipment.

    To begin with, let’s clarify just what is meant by the term vortex burner; technically it’s any burner that swirls the fuel/air mixture at some point; so technically, nearly every stable fuel/air burner would qualify—even some Bunsen burners. Often, the term vortex burner is granted to those that swirl the flames they make. But, causing a flame to swirl happens way too late in the mixing process to provide more than minimal benefits; applied this way the title is complete hype.  

    Forcing an air stream directly at the funnel wall of a linear burner will create a weak vortical flow, but at the cost of also increasing the air/gas mixture pressure through the passage. The special fans on “”V” burners, are used to power up an otherwise passive vortex by creating lateral spin—not forward push—at the funnel entrance; thus, all the energy is spent strengthening vortical flow down the funnel transit, which then increases incoming air flow, while dropping incoming air pressure, by speeding up the gas/air mixture’s forward velocity and spin rate, all the way through the burner to the flame nozzle, where mixture pressure behind the flame is reduced still further. Positive pressure in the burner’s gas/air mixture severely limits how much a flame can be strengthened. So powering up vortical flow, instead of pushing the air, results in much larger and faster flames than are attainable with a standard forced air burner. Every part of a Vortex burner is designed either to enhance, or benefit from, the principles of vortical flow; so the name is actually relevant—not just something that sounds impressive. 

    Once you construct an air/fuel burner that can produce a neutral compact flame (near to total combustion in the primary wave front) from LPG fuels and air, it would seem that it’s the most you're ever going to achieve. So, if the safety cautions to follow make you nervous, why would you go on to build this kind of burner? 

    The truth is that performance involves more than complete and compact combustion. Further improvements can still be made, like: Much greater flame variance (turn-down range); more powerful flames from smaller burners; and the ability to simply change out flame nozzle diameters on a single burner, rather than switching between two or three separate burner sizes; all of these advantages are very much missing in most other fuel/air burners, including high performance jet-ejector tube types (mine).

    Vortex burners are quieter than other turbulent flame burners because of more thorough air/fuel mixing. I believe they come as close to the murmer of linear flames as turbulent flames can.

Note: flame noise is generated by flame variance from millisecond to millisecond during combustion; such variance is mainly the product of imperfect fuel/air mixing; improved mixing results in increased flame stability, and therefore a reduction in flame noise.

These burners provide the same stable performance on the smallest burner you can construct. This enables miniature burner sizes (1/4” and under) with turn-down ranges, from a perfect flame, to be increased by an order of magnitude. When it comes to jumbo size burners (1-1/2” and larger) that extra flame stability happens to be very comforting; if you’ve ever run one of those monsters, than you know just how desirable a smoother flame is.

Four aspects of vortical flow, which make it a dynamic “motor” for burners:

(1)  Fluid movement through a restriction (ex. a funnel) will always create a vortex.

(2)  The forward motion (linear velocity) of a vortex tends to reach about one-half its rotational speed (angular velocity).

(3)  When a fluid (liquid, gas, or plasma) is forced to spiral through a circular reducing passage ( such as a funnel), rotational speed increases the smaller the restriction gets, because, in a vortex, angular velocity (spin rate) increases the closer a spinning fluid is forced to its center of axis; the opposite result of spinning a solid. Thus forward motion is also quite rapid at the funnel’s small opening.

(4)  BUT, fluid pressure drops at the same time; an ideal situation for fuel/air mixing, high feed rate, and especially for maintaining a very low pressure feed into a burner’s mixing tube and flame nozzle areas.

    So, if air pressure from an ordinary axial fan, or squirrel cage fan, will contribute to vortical flow, when run through a funnel, why insist on impeller blades? Direct air flow from an ordinary fan has to be turned almost ninety degrees before it makes a positive contribution to air flow in a restricted shape like a funnel, losing a lot of its kinetic energy in that motion, and it increases incoming air pressure at the same time; impeller blades fling most of their air against the funnel wall close to parallel with it, contributing much more energy to vortical flow, without raising air pressure at all. In fact, since the air is first slung toward the tips of the blades a low-pressure central area is created at the fan, forming a vortex right at the funnel opening, which only increases in power as it travels down the funnel, instead of gradually forming in the funnel.

    Placing a pressurized gas stream just before the mixing tube entrance (near the funnel’s small end) adds air induction, while minimally increasing flow pressure; this synergistic “double motor” effect constitutes a peerless way to feed an air/fuel gas mixture into a gas burner’s mixing tube. A vortex burner employs a modified cone or bell shape, on which an axial fan is mounted; because they are also gas-jet powered (air induced), they will run in both powered and naturally aspirated modes, although not with as much output, without the fan running. But the unique difference in a vortex burner, is that its fan features impeller blades, which are designed to create air swirl, rather than air push, so that they enhance vortical flow somewhat, even without being spun.

    It is all but impossible to establish a stable flame on your burner without swirling the air and fuel gas into a somewhat homogenous mixture, as they travel through the burner’s mixing tube.  Any burner providing a stream of gaseous fuel before the entrance to a cylindrical opening (the mixing tube) will induce air entrainment (via Bernoulli’s principle), a funnel behind the gas stream will also provide swirl to the air entering the mixing tube. All linear burners, unlike jet-ejector designs, need some type of constricting form mounted at the air entrance, to create air swirl for sufficient mingling of air and fuel gas.

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These are venturi burners with some sort of vortex device. But if you meant to ask if the right fan could be mounted on a standard linear burner and act to form a powered vortex, the answer is yes.

The next question that would come to mind is how well would that work? Mabe great maybe poor; to get it right you would need to follow this plan pretty closely, so why would completely rebuild a working burner that way?

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Well, okay; that is showing up my own druthers. From another person's point of view, a significant improvement in performance is worth some minor tinkering. It's my dog and I naturally want it to shine, but your question is quite legitimate; half a loaf is always worthwhile (curse it!)

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The next change that mounting an impeller fan to a linear burner would need is a gas jet and gas tube that stays centered in the burner. So, for the first time in the last twenty years, I can truthfully say something positive for cross-pipes; this makes adding a "vortex devise" on an old linear burner more practical.

Ben,

Thank you for a question that forced me to think outside of the box :rolleyes:

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On 2/16/2018 at 4:36 PM, John in Oly, WA said:

One thing that will come up is how far in to position the MIG tip in the funnel.

I have not changed my recommendation that the tip of the gas jet (whether a MIG tip or capillary tube) should be between 1/4" and 3/8" away from the mixing tube entrance; this is because this distance still constitutes the "sweet spot" for positioning.

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The position of the MIG tip was a detail I wasn't remembering.

I'm waiting for the stainless tube I ordered for the nozzle spacer to arrive, then I should have all the pieces to start this video build.

Then I was thinking it would be fun to make a mold pattern for a funnel with the precise dimensions to fit 3/4" stainless schedule 40 pipe and the diameter of the fan at the other end and the flanges to attach both and cast it in aluminum. It'd save all this mucking about with concentric reducers and SSTs that have to be modified and messed with to make work. Then I'd just have to muck about and mess with casting. LOL

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Casting your own form can also present the opportunity to create a longer funnel and/or a convex shape in the funnel wall; both of which will reduce back pressure against the fan. Be careful, or you will end up with a very in demand burner part $$$. 

Also, you would naturally have to present your burner to the casting group...:D

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Obviously the longer the funnel length the lower the back pressure created, but common sense dictates against going to extremes. I would try twice the diameter for your distance. Most funnel shapes have a straight wall or are slightly concave, but somewhat convex would create less back pressure near the fan. A short section of parallel area next to the large opening would also help keep back pressure away from the fan. 

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The idea would be to have one piece casting that the fan could attach to at the large end, had a reinforced raised area on the outside for the gas inlet tube hole and a coupling cylindrical shape with set screws the mixing tube would fit into.

Something very basic, simple to attach everything to, roughly like this:

Vortex Funnel.jpg

21 hours ago, Mikey98118 said:

Also, you would naturally have to present your burner to the casting group...:D

Goes without saying, of course. The first casting would probably happen at a casting group meeting.

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  Your design would work, but if you deliberately make the flange section 1/2", then the refrigeration tube could still be installed through the flange section; this gives more room to maneuver the tube for bending and soldering the jet in place. The other reason for such a thick flange is to provide enough width for beveling its hole if the fan and flange openings don't match up well enough any other way,

The largest sausage stuffing tube (SKU: 086 from LEM Products) is meant for use with 2” sausage casings; spacer rings can allow it to be used on 1-1/4” and 1-1/2” burners, but for both of these burner sizes, use the strongest axial computer fan you can find, to make up for less than maximal air scoop diameter

21 minutes ago, John in Oly, WA said:

Goes without saying, of course. The first casting would probably happen at a casting group meeting.

Be sure to late me know which meeting.

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I can make the flange thicker. Probably make the funnel a little longer too. I was hoping to match the "ideal" fan, size and cfm, to the funnel so it's as easy as possible to spec out the exact fan and then just bolt it up, cut a stick of 3/4" schedule 40 pipe to the right length and fire away without having to do any machining or modifying.

Then get wild and stick one of Frosty's NARBs to the end of it and have a real Rocket 88, or Rocket 23 or Rocket (however many nozzlettes are in the thing).

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