Who Will Stand This Mighty Destroyer of Pretend Engineers?

If it is the roddles I met, then he was definitely a theory boy. Glorified storeman at best.

OK, no flaming on my threads.

You _must_ be respectful to every clueless piece of bat crap here on newsgroups.

Bret Cahill

You get to wear asbestos threads, f****it.

Hope you get mesothelioma.

Nope. Illegal.

Pathetic.

. . .

Ain't gonna happen. You must inhale asbestos to get mesothelioma and even then the disease is rare.

Pathetic.

Bret Cahill

Your problem.

And that will happen when you're wearing asbestos, child.

Wrong, as always.

So you've re-invented the fluidized bed?

How does your version compare with, say, a Fischer-Tropsch slurry reactor?

While you're at it, I'm really curious to see your derivation of the heat transfer coefficient.

Michael

Wow, you used to work for Studiomaster?

Did they get bought out at some point?

Do you have a website of your designs?

Thanks,

Michael

It's a heat exchanger, not a reactor.

For example, breakup of catalyst particles isn't an issue here because the particle bed can be made of hollow metal spheres, metal coated glass or ceramic bubbles.

It's empirical. You can easily run your own tests if you don't trust the numbers in the literature. Set a cooler of ice water up on a shelf and siphon the water through an aluminum or copper tube in the bed and measure the temp. increase.

Unless there's been some recent breakthroughs, the theory still isn't completely understood.

One theory claims that the particles tunnel through the boundary layer, contact the surface and then back out to transfer heat with the gas. They set up the problem with these unconvincing drawings of a sphere contacting a flat surface. It's a 2 or more step process and even with millions of contacts/second, it's a dubious theory.

Recently I heard of another more plausible theory that claims the boundary layer thins or dissipates with fluidization. The effective density, Reynolds number and turbulence increase so the flow situation is closer to a liquid than a gas.

It'd be nice for them to get the theory right. It could save a lot of time optimizing.

What's really interesting is out of a couple dozen ME books on heat transfer, particle bed fluidization will get mentioned maybe once in a foot note. It simply isn't studied in ME. All the work has been in chemical engineering, starting back in WWII to crack petroleum.

Another example of the desirability of multidiciplinarity.

Bret Cahill

Are you using the heat transfer text by Incropera and De Witt?

Perry's Chemical Engineers' Handbook gives a good overview of heat transfer and fluidization theory.

Michael

What's the HX mechanism?

Does the boundary layer stay intact with the particles passing through the layer?

Or does the boundary layer breakdown?

What's really interesting is out of a couple dozen ME books on heat transfer, particle bed fluidization will get mentioned maybe once in a foot note. It simply isn't studied in ME. All the work has been in chemical engineering, starting back in WWII to crack petroleum.

Another example of the desirability of multidiciplinarity.

Bret Cahill

Beats me... what HX mechanism?

What's the Reynolds number? Above 2100 or so you have turbulent flow, and the best you can do is use correlations.

You're a Mech E, huh? Where/when did you graduate?

Michael

My bad... for cylindrical boundary layers, if the Reynolds is 40 to

5000 you form a Karman vortex trail (street?). See also D'alembert's paradox 'Alembert's_paradox Michael

What's their theory on why fluidization works?

Glass microspheres look remarkably like a boiling liquid but looks can be deceiving.

I can't say. With particle-gas, the "density" is of course much higher but the "viscosity" increases as well. The HX improves with smaller particle size down to 10 microns where it starts to go back down.

With liquid-particle the HX will max out at 0.5 - 1 cm dia because smaller particles just increase the "viscosity."

It's not my job to figger it out.

Like I said, they never mention fluidization in ME. I studied it very little formally. I read up on it later trying to eliminate film cooling in gas turbines and to increase HX in Stirling.

Bret Cahill

Oh, HX = Heat Transfer?

Stirling... good luck. Entire companies have tried, and apparently failed, to commercialize that. Keeping the working gas from escaping from the seals is apparently... difficult.

Michael

Another one of those technologies that does not scale up well.

Just make a gigantic version of the drinking bird. Heat its' ass and have the beak dip in a river. :)

That's the happin' field. What gets me is the average 1 star chef knows more about HX than most engineers, at least in a qualitative sense.

Hundreds maybe thousands.

San Diego Gas & Electric recently ordered 16,000 25 kW dishs from Stirling Energy, eventually more for a total of 48,000 for a 1 GW plant, the biggest solar thermal in the world.

After 200 years Stirling may finally become a production engine.

Even gas turbines only took 80 years.

They pump it back into the cylinder. If the generator is inside of the housing then exterior dynamic seals or glands are eliminated, i. e., Sunpower.

There are only two low parasitical loss strategies to increase HX in a Stirling:

1. Increase pressure to 50 - 200 bar 750 - 3,000 psi to increase density to increase Reynolds to increase Nusselt to increase the HX coefficient. This is the most popular strategy in Stirling today.
2. Another is to increase surface area. By a lot.

The best way to do this is with slightly flexing heat exchanger _inside_ of the cylinder. Coils of rectangular thin tubing in the heater side compress flat which accomplishes the same thing as the conventional displacer, forcing the gas through a regenerator and on to the cold side.

On the addition-of-heat stroke the heater coils expand separating slightly to allow the gas to flow in and be heated. A thermofluid is pumped through the coils.

This could be open cycle air -- valves on the cold side -- as this heater will be effective even at atmospheric pressures.

It could easily be designed to keep the stresses and strains below any fatigue limit at operating temp. by increasing the cylinder size.

Everything deflects to a certain extent which is how statically indeterminate structures are evaluated. That's where I got that idea.

Bret Cahill

Bret Cahill wrote: ...

Interesting. How thick must the (stainless steel) wall of the gas pressure vessel be, to support a MAWP of 3,000 psi?

Let's say the outer wall of the pressure vessel is exposed to concentrated sunlight at 400 C. At steady state, what will be the temperature of the inner wall?

Michael

The top [hot side] of a beta cylinder is spherical to reduce stresses.

More like 1,000 C. They use an aperture and maybe heat pipes.

They're getting over 30% efficiency, better than anything else that affordable.

It's a derivative of a Swedish sub engine.

Bret Cahill