[Stoves] Cajun Rocket Pot

Andreatta, Dale A. dandreatta at sealimited.com
Mon Jul 29 16:31:13 CDT 2013


Yes, a TLUD would have a lot less soot.  Charcoal stoves too.  

 

The message from Todd Albi mentioned a Turbopot, whose website I just
checked out.  It also claims fantastic results.  Who knew there were all
these finned pots out there?

 

Dale

 

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf
Of Tom Miles
Sent: Sunday, July 28, 2013 2:27 PM
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] Cajun Rocket Pot

 

Is a TLUD likely to have less soot buildup on fins?

 

Tom

 

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf
Of Andreatta, Dale A.
Sent: Sunday, July 28, 2013 11:12 AM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Cajun Rocket Pot

 

I like it!!!

 

As some of you know, I spent a lot of time around 2007-2008 working on
finned pots, and never really got them to work well.  I didn't try this
type of "pin fin" design because I couldn't figure out how to make a
prototype.  

 

With this pin fin design (that's what mechanical engineers call this
shape of fin) you increase the heat transfer area, but unlike the fins I
worked with, you don't significantly change the flow of the gas.  You
get high convective heat transfer coefficients.  Hot gases impinging on
a surface (hitting the surface from a perpendicular direction) usually
gives better heat transfer than hot gases flowing parallel to a surface.
The basic tests that have been done prove this, at least with industrial
fuel flames.  

 

I expect that with a sooty flame, you could use a brush to scrape off
most of the soot, and what you don't get this time you can get next
time.  Thin layers of soot wouldn't have much effect.  Perhaps arranging
the fins in rows rather than circular arrays would make them easier to
clean quickly.  

 

I expect that emissions per unit of time will increase, since you are
quenching the flame more quickly at the bottom of the pot and stopping
the reactions that would otherwise burn up some of particles and CO.
The effect might be small or large.  On the other hand, if the time to
boil is greatly reduced, the total emissions might be a lot less.  

 

I expect that you could make a pot out of cast aluminum with the fins
cast in place.  You could use tapered pins to save material and improve
castability.  You could probably also use sophisticated welding
techniques, as has been described, or possibly furnace brazing
techniques.  

 

The material of the pot doesn't make much difference.  Since all metals
are much better conductors of heat than gases, it doesn't matter whether
the metal is much better at conducting (stainless steel) or much much
better at conducting (aluminum).  It would mostly then be a cost and
manufacturing issue.  

 

The fins must be bonded (welded, brazed, soldered, cast in place) to the
pot itself, otherwise there is too much resistance to heat transfer
across the interface.  

 

What to do next?  Where does one get one?  If I can get a sample I could
test it out on a variety of stoves, rocket, charcoal, open fire,
gasifier, LPG, fire-in-a-bucket, etc.  I could prepare a quick report by
the next ETHOS time.  Or, someone who does experimental work full time,
such as Apro or many other labs, could do a better job in less time.
What I'm saying is that this is a very exciting development, that could
make a huge difference in what we do.  We should pursue this quickly.

 

Dale Andreatta, Ph.D., P.E.

 

 

 

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf
Of Dean Still
Sent: Sunday, July 28, 2013 11:36 AM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Cajun Rocket Pot/ capacitive discharge stud weldie

 

Hi Lanny,

 

We tested a couple of pots with fins but the space between the fins
clogged up quickly with soot, a good insulator.

 

Best,

 

Dean

On Sun, Jul 28, 2013 at 5:21 AM, Lanny Henson <lannych at bellsouth.net>
wrote:

	 

	Lanny have you seen capacitive discharge stud welding?


Yes I have a stud welder but I did not realize it would weld dissimilar
metals especially aluminum to anything else.

Stud welding is very finicky and will leave a blemish on the opposite
side of thin metal.

When a stud weld fails you have to grind the surface to clean it up
before rewelding.. How are you going to do that if it is between the
other studs?

Attaching studs, fins or anything to a pot is going to be problematic,
but attaching something to the pot holder may be practical. The heat
transfer may not be as good as having something attached to the pot but
it could possibly improve the heat transfer.

Lanny Henson

----- Original Message ----- From: <ajheggie at gmail.com>
To: "Discussion of biomass cooking stoves"
<stoves at lists.bioenergylists.org>
Sent: Sunday, July 28, 2013 5:23 AM
Subject: Re: [Stoves] Cajun Rocket Pot

[Default] On Sat, 27 Jul 2013 20:48:02 -0400,"Lanny Henson"
<lannych at bellsouth.net> wrote:

I like creative people and take no pleasure criticizing their work but
it is going to be too expensive and difficult to make with all the pegs.


Lanny have you seen capacitive discharge stud welding? This would
allow welding of dissimilar metals to the pot in any pattern. I have
no idea of costs.

Have you done heat transfer tests with your 4mm aluminium pot compared
with the thinner stainless one? Stainless is a notoriously poor
conductor of heat and theoretically would need to be just under a
tenth of the thickness of aluminium for the same conductivity, but I
do use stainless pots at home.

Finally can you explain the difference between a vat and a pot?

Paul I do consider this to be important because biomass stoves have an
inherent problem with heat transfer compared with natural gas or LPG
so improvements in heat exchange will have high benefits.

AJH




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