[Stoves] Cajun Rocket Pot

[Tom Miles]

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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