[Stoves] Cajun Rocket Pot
Jonathan P Gill
jg45 at icloud.com
Mon Jul 29 05:48:11 CDT 2013
Todd,
I find that a TLUD with a well tuned air/fuel mix, that also has good turbulence in the mix, will produce little soot on pot bottoms. Proper carburation of a turbulent fuel air mix makes for a cleaner burning TLUD.
Excessive soot build up is a good indication that the carburation and turbulence of the mix are sub optimal.
Regards,
Jock
On Jul 28, 2013, at 11:42 PM, Todd Albi <todd.r.albi at gmail.com> wrote:
> Subject: Cajun Rocket Pot / TLUD Soot
>
> Soot is an end product on all pots used on biomass stoves with or without fins or skirts. Heat transfer is increased by adding more surface area to cooking pots with dowels, finned ribs, corrugated ribs, rows of fins or full skirted pots as discussed. Steel woks with lamented cast iron bases with fins have been available in China for quite sometime. We have both in our SilverFire showroom. They are designed specifically for biomass. Finned pots specific for LPG have also been available for a number of years.
>
> The Chinese Enron turbo pots have been marketed in the USA for several years (www.turbopot.com). Rebates for Enron finned pots are available from utility companies in the USA for LPG savings. The LPG fin design on Turbo pots differ significantly from the biomass design. Narrow LPG finned pot channels clog with soot and the end result is that the soot negates heat transfer, if used with biomass. Fin designs for biomass cooking are significantly wider and work well. Time to boil is significantly reduced.
>
>
> The ease of cleaning and product acceptance is also important, as Dale touched upon. We had early prototypes of both fin pot & skirted pots fabricated in 2008. I was not a proponent of the Aprovecho fin pot. It made no sense for the end user. The early design had fins that extended from the base and up the sidewalls of the pot. We would have had to provide tetanus shots for end users, had that design ever reached the market. The exterior design was unacceptable. Cleaning or handling the pot was a handling hazard.
>
>
> Our production pot we introduced to the introduced to the market was the skirted pot. It cut approximately 5 minutes to time to boil in our early WBT work. I brought the skirted pot to market though, for the important fact that we designed the skirt to protrude below the cast iron cook top. This important design feature reduced the chance of the pot sliding off the stove to prevent burning the cook or children. Since soot did not accumulate on the exterior skirt, it also meant less cleaning for the cook, compared to the finned pot. The skirted pot was more acceptable than our fin pot design. Combining a skirt and fins would provide even greater heat transfer. A well-designed pot must be easy to clean.
>
>
> Todd Albi, SilverFire
>
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>
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> On Sun, Jul 28, 2013 at 11:26 AM, Tom Miles <tmiles at trmiles.com> wrote:
> 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.
>
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> 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.
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>
> 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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