Calculating number of holes for ribbon burner???

[Peppie]

Buzzkill.

You are the man! You stated in another thread," How small can I make it, and still be able to do what I intend to do?"   Something like that.

I am now headed to plan "B"

Thanks. Back to the white design board.

Peppie

[JHCC]

9 hours ago, Peppie said:

The length of 20" would be used once in a blue moon for ornamental pieces.

My friend Kim does incredible ornamental work with a small (~300 cubic inch) gasser and a coal forge with no pass-through. 

If your truly thinking once in a blue moon, you’d be much better off making a single-use solid-fuel forge ad hoc. Even a charcoal-filled trench dug in the ground is better than an overbuilt gas guzzler that you only use at full capacity once or twice a year. 

[Peppie]

JHCC ,

after reading several post here on the forum, I have went back to the drawing board. Leaning towards an expandable design ,when and if needed.

Thanks for all the info this far

Peppie

[D.Rotblatt]

14 hours ago, Peppie said:

back to the drawing board

Take a look at a tabletop forge, looks like a very adjustable build.  It uses a ribbon burner pointing up. It's discussed on P. 39-40 of the Forges section here on IFI. 

Also look at this build of it, this is the earliest one I've seen.  Flemming Knives; shop tour; second picture: http://www.flemingknives.com/ribbonforge.htm

 

 

[Frosty]

Peppie: Your drawing a few posts back showing the blower, straight length of pipe, the gas jet, a 90* elbow another short straight length to a T then valves and finally the burners looks good to me. Sure it may need some adjustments but it should work well enough.

The proper fuel air mix is established by the blower output and fuel from the jet. Changing the position of the valves before the burner blocks will NOT change the fuel air ratio. If it does the needle valve will take care of it.

Mixing air and fuel in a gun burner is often done by putting a turn after the fuel is introduced. The 90 elbow does the job and then it hits the T fitting making more turbulence and further mixing. It's all good. 

Personally I think you're making another future dust collector. Almost all of us have built way too large forges when we started out, I have a couple collecting dust and one silly too big forge still in use. 

Rather than build one huge forge you may only use to capacity once a year or two how about making two smaller forges you can connect if you need a big one? Believe it or not it's easier to make two smaller forges than one big one. Trying to apply a coat of hard refractory say Kastolite 30 that deep in a tube will be a PITA. I hated spreading it in a 6" deep space through a wide door. 

Frosty The Lucky.

[Peppie]

TY, DRotblatt. I like the design of the floor forge in the link you provided. I will in corporate some of the ideas in my build.

Frosty, TY for the input, I value your opinion. I think you have forgot that in this forge design that it will be divided into 2 chambers. Each chamber will be approx 750 cubic in. The chambers will be separated by a removable wall. I am going to try to reduce the interior cubic  inches by approximately 200 cubic inches per chamber before I start to build. 

This will be my second forge build. I currently run a 350 cubic in forced air forge, It works great....but I am not pleased with the flame from the burner pointed directly on or near the steel in the chamber. Sure makes for alot of decarb.

Peppie

[Peppie]

I am going to learn by ya-alls mistakes.I have down sized the "single" chamber to 380 cubic inches. Knocked 400+  cubic inches.  It will still be a floor mount ribbon burner, 2" X 8" with 24 holes. Total length  of the chamber will be 12".

Here is the question,  has anyone tried using the bendable straws for the burner ports? Would like to direct the ports e it away from the curved side wall . Wouldn't need to bend the straw anymore than 10 degrees at the most. Can I burn the straws out? Or do I have to pull them out?

[Frosty]

I tried straws to see how they work but some collapsed when I cast the block so I filled them with sand the next time which worked but it was still more work than using crayons. Not saying crayons are better I just like them better because they're less work. I may have been doing it the hard way though. I inserted the straws in the bottom form and filled them with sand then lifted the sides off the form so I could clear out the spilled sand, then put the form back together. More steps for no appreciable improvement and I'm basically a lazy guy. Something has to work better if its going to be more work. 

I angled outlet holes by tipping the wood bottom of the form when I drilled the holes that hold the crayons. It worked nicely, that burner's flames are aimed away from the door slightly and produce less dragon's breath. 

Frosty The Lucky.

[Buzzkill]

Hot glue sticks are both solid and flexible.  However, if you want to have them aimed a certain way then you'll need a block at both ends to hold them in place while the casting material cures. IIRC the sticks I used had an actual diameter of 9/32".  I'm not sure how that compares to crayon diameter.

[Frosty]

I'd have to measure a crayon or . . or . . . or read my own posts!  

When you tried glue sticks out I played around with them a little but thought they were too flexible and cost a lot more than the BIG boxes of crayons at Wally World during back to school sales. Yeah, I do have a couple unopened giant boxes, IIRC 128 or maybe 256 crayons each. On sale these were cheaper than a small pack of glue sticks so my Scotness said CRAYONS!

Frosty The Lucky.

[Peppie]

I did a search for the twisted birthday cake candles.... didn't think they were long enough at 2.5"???

[materman]

Take it with a grain of salt for it was just what I've heard and I am no expert, but refuring to the original post, I have heard you want the holes in the burner to equal the diameter or the air pipe coming in, or equal flow capacity. And if this hearsay is incorrect, enlighten me.

[Peppie]

Materman,

I have read the same info. I plan on increasing the intake pipe, compared to the total square inches of the port holes. .... With in reason. Will try to work in 1/2" diameter increase.

[Buzzkill]

I'm not convinced there is a direct, or at least easily to calculate, correlation.   I just did the math on the NARB that I posted (page 6 in the NARB thread I think).  The inlet pipe area comes out to 0.302 square inches for a 1/2" schedule 40 pipe. 

If I did my math correctly the sum of the combined areas for the 14 holes of 9/32" diameter is 0.870 square inches - nearly 3 times the total area.  I had way more holes to begin with and plugged them off until I got a stable running burner which didn't backfire until really hot at low (2 psi or less) pressure.  

So, regardless of what the conventional wisdom may happen to be, what really matters is how the burner performs in your forge.  For a naturally aspirated burner, the feed tube diameter is important with regards to getting a good fuel/air mixture.   For a blown burner the feed tube doesn't have as much effect on the fuel/air ratio.

My advice is start with a design known to work well and maybe extrapolate a little from there if that design isn't perfect for your needs.

[Frosty]

I believe I said there is NOT a direct correlation in my original post. The smaller the outlet the greater the ratio between area to circumference/surface area and friction. The first test block I made had about 30% more area than the 3/4" mixer tube and that wasn't enough, back pressure killed induction in the T. I put my calculator after that and started drilling more test blocks. I bracketed the correct number and zeroed in. 

I also eyeball guesstimated a correction for a hole drilled in wood having more friction than one cast in hard refractory when I cast the first block. I lucked into that one. 

It worked for me surprisingly well. I'd be shocked beyond belief if people didn't come up with better: configurations, ways to make them and performance. There's NO WAY I lucked into a multiple outlet burner that can't be improved upon. 

Frosty The Lucky.

[AlexKelamis]

If you want equations to understand the flow, resistance, and overall fluid Dynamics of a ribbon burner, just look at the fluid Dynamics equations:

v=Q/A, where v is velocity (cm/sec), Q is flow (mL/sec), A is area (cm²).

Q=∆P/R, where ∆P is pressure difference (pressure beginning minus pressure at end), and R is resistance (see below next).

R=8nL/πr⁴, n is viscosity of fluid (negligible, or 1, for gas), L is length of tube (cm), r is radius of tube.

For ribbon burners, it is a parallel series of tubes, nozzels, etc.  Point is, it's parallel.  Now, the total resistance of a parallel system is:

1/R[total]= 1/R[1] + 1/R[2] + 1/R[3] ....

This means the total resistance of the entire parallel system will be LESS than any single individual "nozzel" resistance (calculate it if you dont believe me).  Put another way, as the number of nozzels/outlet ports increases, the total resistance of the system (burner) will decrease.  As the resistance decreases, the flow through the system will increase (ie: you will be using more gas overall--thats not a brain-buster).  As the number of nozzels increases, you can push higher volumes of gas through.  But, if you keep your PSI at the regulator the same, you'll obviously have less flow, and less velocity and pressure difference, coming out each nozzel.  

So, again none of this should be surprising.  I'm just explaining it so people will realize the equations are correct.  Further, if you are designing something involving explosive gas, it doesn't hurt to "check" your plans with the equation.  Hopefully the equations will be useful.  Without having more info myself I can't provide much more. But, if you want my input feel free to ask.  I'll tell you what I know.  If I don't know the answer to something, I'll be the first person to say "I don't know".  Best of luck.