Exhaust Duct Engineer 1

[TugboatEng]

I have an upcoming project that requires an offset in some 16 inch pipe but don't have room for two 90° elbows. I believe this can be achieved using rectangular ducting but there are complications of very high vibration and rapid temperature cycling of up to 1000°F within minutes. What type of engineer specializes in this type of design? This one is way over my head. I don't know where to look.

 

[mfgenggear]

Tugboat

Look into a supplier that does cnc tube and pipe bending. Also might consider making a bend
To fit the trim and weld in place, not the joints.
Contact a tube and pipe supplier.
Discuss your needs and do concurrent engineering. They will help you design it.

 

[dvd]

The devil is in the details. Possible bellows expansion joint offset?

 

[rothers]

Yes, more details required. How much offset is required ? Could you not do a lazy offset with 2, say, 2 x 30 deg elbows.

 

[Stick.]

What's inside/outside the pipe (I'm assuming a fluid/gas of some kind)? Any pressure or other loadings of note? Adding in an offset might mean you need to reevaluate supports (for things like thermal growth allowance, unbalanced pressure loads, etc), but maybe that's not a concern at this scale.

The temperature kinda makes me think gas turbine/power generation type stuff, but I'm kinda shooting from the hip there.

 

[TugboatEng]

It's a diesel engine exhaust. I have 2 vertical pipes that are offset by 48 inches. I need to connect the two pipes but have only 24 inches of vertical space to do it. The pipe diameter is 16 inches. Flow velocity in the 16 inch pipe is in the neighborhood of 9000-10000 feet per minute. Pressure ~1 psi.

 

[mfgenggear]

Tug
Maybe weld the two pipes into one,
In my first post , I suggested to speak with a pipe and tube fabricator. Who could help build your exhaust. Could be over kill.

Ever install exhaust headers on a hotrod. Same concept.
Build out side then install the entire exhaust and bolt on. Keep altering until it fits.

 

[TugboatEng]

16 inch elbows are 24 inches tall. If I use two elbows to make my offset I would already be at 48 inches. I am thinking of building a box with offset 16 inch inlet and outlet but I not only need to estimate pressure drop but also design to resist cracking due to vibration and extreme temperature variations.

 

[mfgenggear]

Tug
Plenty 16 inch pipe, a cheap chop saw, and a mig or tig welder. And some welding clamps. And get a young sheet metal tech, and welder. How bad of vibration. The parent material will depend on your budget. Vibration should not be a problem if dampeners are installed to hold exhaust in place.

 

[MintJulep]

This is gonna be hard Tug.

Convincing that much flow to suddenly change direction takes a lot of force.

It's going to add a lot of restriction. How much can the engine tolerate?

Because of the forces involved, everything will need to have a solid load path to structure; but because of the thermal expansion everything will need to be flexible.

You'll want turning vanes inside to help reduce the restriction; but because of the temperature and velocity erosion will be a problem.

Every design choice will be a compromise.

Disqualify anybody who replies to your inquiries with "sure, no problem" - they don't understand how difficult this will be.

You want the guy who turns you down, because that's the guy who understands.

Look for firms that do power plants.

You really can't move the upper stack over 48 inches?

 

[catserveng]

Tug,

4 possible places who may help if they are still around, been a while since I've gotten involved in marine repowers or upgrades.

Halyard in Dorset UK, they helped with 3600 marine retrofits in some tight installations, but maybe too far away from you I think.

Centek Marine, they supported a number of marine customers in the gulf, as I remember very good work and came up with good solutions for tight installs, South Georgia

Northern Marine, as I remember they helped with some issues on exhaust systems on some early tractor tugs for CAT and Crowley several years ago. Anacortes WA

DeAngelo Marine in Fort Lauderdale, design and custom fab of dry exhaust for both a 3500 and 3600 retrofit/upgrade, their backpressure calcs were dead on during sea trials.

Hope that helps, MikeL.

 

[mfgenggear]

Tug

https://hardydiesel.com/product/diesel-generator-exhaust-kit/

 

[mfgenggear]

It's only hard when your naive.
Seeking advice is a virtue.
I always look at issues with glass half full, not half empty. I had to do difficult projects
Not because it was easy, but because it was difficult. And I had no choice it was thrown in my lap. Do your research and accumulate suggestions then make decision. But an educated decision. Don't ever guess.

 

[TugboatEng]

Thanks Cat. We're attempting to get rear facing exhausts but that is proving to be difficult, no parts available, and expensive because we also need the correct exhaust enclosure for the rear facing outlet.

Mfgenggear, the previous project did a 360 loop in the piping. It works, but I want to do better.

Mint, we have restrictions allowances from the mfg. Our existing system is relatively short so we have a room to work within the restriction limit. After all, the one system already in operations has a 360.

The good news is that our system spends little time at max flow, I don't think erosion will be too much of an issue.

The driveline dictated the engine height. Visibility and clearance issues dictate the stack height. We're already doing the steel work to raise the stacks as high as practical.

I understand the bellows situation is not ideal, we have worked out a solution with our supplier that has been successful for years in service.

 

[JStephen]

They DO make short-radius ells also, length = nominal OD.
Mitered ells perhaps an option.
I used an item very much like your sketch to connect my dryer vent up. I suspect it doesn't come in a 16" size!

 

[dvd]

it seems like two 180 bends or four 90 s.r. bends would do the job if you swing the elbows to keep your 48" spacing, i.e., don't go there in a straight line.

 

[TugboatEng]

The first two bends are already 48 inches long. I don't have room for the next two. I have to do a straight line.

Do short radius bends exist in 16 inch? Don't they cause a lot of back pressure? Are they expensive or have lead times to purchase?

I have to do this project 8 times so I have some budget to work with upfront. That's why I want to hire an expert to work through this with me.

I really appreciate ideas. I really appreciate contacts. I want to thank everyone for their contributions.

Keep them coming, too. I'll be watching.

 

[mfgenggear]

Tug
What is the center to center.
My thoughts neither design is efficient.
Gaining from round to ducked may be an issue.
Build a flanges at both interfaces . With metal gaskets, you need a smooth transitioning.
Making progress keep brain storming.

 

[MintJulep]

 

[3DDave]

With an angle grinder or a cutting torch any bend can be a short bend.

I think a CFD package could do most of this; doing the transient response is going to be difficult and the vibration is into the multi-physics arena; maybe a COMSOL consultant.

With that immediate sharp turn this is practically dead-heading about half the flow into a pressure rise and then the pressure re-accelerates the flow only to be neatly partially dead-headed at the next sharp turn, with another pressure rise.

Turning vanes into a rectangular section would help with that, but a conversation with Hastelloy may be needed to get vanes and an impingement surface that last.

Perhaps moving the bellows farther downstream, past the pressure rise and the highest temp would be a help.