Fluidized Bed Gas-Gas Heat Exchanger

For decades chemical engineers have known that the particles in a
fluidized bed "scour" through the thermal boundary layer resulting in
heat transfer coefficients an order of magnitude higher that with the
gas alone.
Little to nothing has been done with this phenomenon in mechanical
engineering. "Fluidization" or "fluidized beds" is never mentioned in
any textbooks or handbooks on heat transfer.
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Bret Cahill
Reply to
Bret Cahill
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Baloney. Just opened my old text. Chapter 7-7 Heat Transfer and Flow in Packed Beds. Basic Heat Transfer, by Kreith and Black. 1980.
Reply to
Ed Ruf
Reply to
Bret Cahill
Like I said, absolutely nothing on _fluidization_ where, at a threshold flow rate, the bed expands from 50% to over 500% and the particles are in constant motion and the two phase flow looks like a liquid.
Packed bed particles do not move.
Bret Cahill
Reply to
Bret Cahill
Dear Bret Cahill:
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Looks like a lot has been done on this subject in mechanical engineering (as Google will attest... from the first 20 hits with fluidized bed heat transfer
Note that some of those links are to textbooks.
I suggest that the topic is a little exotic for *introductory* textbooks...
David A. Smith
Reply to
N:dlzc D:aol T:com (dlzc)
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Not one mentions fluidization for the obvious: a heat exchanger!
Google "runaround loop" and "fluidization" etc. and you will get ZERO relevant hits.
Search
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-- NOTHING!
Bret Cahill
Reply to
Bret Cahill
Dear Bret Cahill:
...
I have never heard of a "runaround loop" until you brought it up. Neither my heat transfer, my refrigeration, nor my solar texts have anything on it. Not very many hits on Google either...
But how you would fluidize a bed with one fluid, then fluidize it with a different fluid, might be a bit hard to do. In most processes, you want the two fluids separated.
If you are less specific in your search, I find 167 hits, some relevant (some with your name on them...) "runaround" fluidized OR fluidization
Fluidizing requires a lot pumping of energy. So it is usually reserved for difficult media.
David A. Smith
Reply to
N:dlzc D:aol T:com (dlzc)
It's been around for awhile.
Basically you couple _two_ heat exchangers with a liquid loop turning them into one. Think of two radiators with the coolant connected.
Until now no one has used it with fluidization.
Zero _relevant_ hits with "fluidization."
They _are_ separated. Click on the link in the OP.
No mechanical or dynamic seals either.
The liquid is in the coil and the gas and fluidized particles are in the upflow tubes.
. . .
Ever mess with the paint additive [filler] 3M "glass bubbles?"
Microspheres fluidize at small fractions of a psi. Increase the flow from zero and eventually the bed expands by a factor of five then fluidizes.
Shake a flask of bubbles and it will look exactly like liquid milk.
For low pressure ratio regenerated gas turbines pumping losses would be less than 1% of output.
Bret Cahill
Reply to
Bret Cahill
"Document Not Found"
Is there an error in your link or is access restricted?
Thanks, Glen
Reply to
Glen Walpert
That link doesn't work. It only gives a "Document Not Found" error.
Can't you just describe how its supposed to work, instead? Is it something along the lines of moving the solid particles from the hot liquid to the cold one?
S.
Reply to
Sevenhundred Elves
Come on Bret give up pushing BS, type "fluidized bed" in google
The fifth entry is:
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First entry here is:
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What more do you want?
Reply to
Ed Ruf
People burn coal in fluidized beds, so they must know something about the heat transfer. They've got to get the heat out of the bed so it can be used to make steam.
Olin Perry Norton
Reply to
Olin Perry Norton
A 95% effectiveness heat exchanger with pumping losses less that 0.1% of duty.
Bret Cahill
Reply to
Bret Cahill
In that case the fluidised bed is usually limestone, which removes the sulphur oxides released by combustion of the coal in the fluidised bed. The heat transfer uses the exhaust gases coming off the bed, the input being pulverised coal and air. There could also be some steam in the air to regulate the temperature and avoid slag formation. The exhaust gases will be a mixture of Nitrogen, Carbon dioxide, Carbon monoxide, Hydrogen and various hydrocarbons, which will burn in secondary air. That's when the heat transfer to the boiler or heat exchanger takes place.
Reply to
Terry Harper
Apparently it never occurred to anyone until now to exploit the high HX of fluidization for it's own sake _without any reaction or combustion process_.
If the link doesn't work look under "Fluidization" in the "Files" section of Yahoo Groups' Hot Air Engine Society.
Bret Cahill
Reply to
Bret Cahill
According to this web site:
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some fluidized bed combustors do indeed work as you describe, extracting heat from the relatively clean gas after it leaves the bed, but it also describes 1st generation pressurized fluidized bed technology which has heat exchangers (boiler tube bundle) immersed in the bed.
Olinn Perry Norton
Reply to
Olin Perry Norton
All the HX done with fluidization so far has always been directly in combination with combustion or other chemical reactions.
No one has exploited the high heat transfer rates of _inert_ fluidizing particles to build and optimize a cheap, compact, high effectiveness, low pumping loss gas-gas heat exchanger that could be used, for example, to "breath" highly insulated homes and buildings in cold climates. The air in a 3,000 ft^2 house could be exchanged several times a day with very little additional heat or mechanical power consumption. This would be an easy home brew project -- less than $150 - $200 in parts and a few nickles a day to operate.
Low pressure ratio regenerated engines have very high efficiencies but the regenerator is always too big and expensive, leaks because of mechanical/dynamic seals and has high pumping losses.
A 20 kW 2.2 : 1 p. r. regenerated gas turbine would boost mpg in a series hybrid to 70 with almost as little smog as external combustion.
Locomotives need to get away from the smoggy 6,000 degree 4,000 psi diesel and go to low pressure ratio regenerated GT.
Bret Cahill
Reply to
Bret Cahill

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