[Stoves] Cajun Rocket (finned) Pot, and Eneron Finned Pot

Wed Nov 20 16:29:53 CST 2013

Hi Dale,

The Eneron pot clogged with soot quickly because the fins are so close
together. Might work great with a super clean stove but not with a regular
wood stove like a Rocket.

Best,

Dean

On Wed, Nov 20, 2013 at 2:25 PM, Andreatta, Dale A. <
dandreatta at sealimited.com> wrote:

> All of Crispin's comments are correct, and I suppose I should have
> included the mass of the pot and its energy gain to get the true energy
> transferred.  Still, my view is that whether the Cajun pot is 16% better or
> 10% better than a regular pot, that's not enough to get excited about.  If
> someone want to redo the calculations I can send them the Word version of
> the report and they can edit it so that all the numbers are there.
>
>
>
> I've attached a report about another finned pot, the Eneron Pot.  This
> report covers 3 types of gas burners of the type used in restaurants.  I
> chose to test the Cajun pot rather than the Eneron because I believed the
> Cajun pot would be very good, and the Eneron not as good.  The first of
> these beliefs was wrong, so perhaps I should have tested the Eneron pot.
> Perhaps someone else would like to test it?  With a couple quick tests you
> could probably determine whether it is promising or not.  I might do that
> some day, as well as test variations of the Cajun pot.
>
>
>
> With regard to Ron's questions, in my calculations I always included the
> evaporated water (except in the simulated open fire test where there was
> virtually no evaporation) but never the mass of the pot.  The formula for
> energy gained by the water would be:
>
>
>
> (Mass of water times temperature gain times 4.186) + (Mass lost through
> evaporation times 2250)
>
>
>
> Divide this number by the number of seconds elapsed during the test period
> gives you the power into the water in Watts.  This works for high or low
> power, or the overall test, or any other length of time.
>
>
>
> The estimated 700 Watts lost from the pot was not included in any
> calculations.  I gave that number as a way of explaining why the ratio of
> times to boil was greater than the ratio of heat transfer efficiencies.  As
> you approach the boiling point the net heat gain by the regular pot is
> about 1128 - 700 = 428.  The net heat gain by the finned pot is 1227 - 700
> = 527, or about 23% more.  If you had a pot that produced 701 W of heat
> transfer it would approach the boiling point quickly and then take a
> reeeeeeeeeeealy long time to fully reach boiling.  (It seems that half of
> my tests go this way!)
>
>
>
> Dale
>
>
>
> *From:* Ronal W. Larson [mailto:rongretlarson at comcast.net]
> *Sent:* Tuesday, November 19, 2013 12:34 AM
> *To:* Discussion of biomass; Andreatta, Dale A.
> *Cc:* Crispin Pemberton-Pigott
> *Subject:* Re: [Stoves] Cajun Rocket Pot Tested
>
>
>
> Dale and Crispin:
>
>
>
>    This is to try to close the gap a bit.  Dale reports for his home gas
> range testing two differences in efficiency:  8.8 and 13.5  (the "knobby
> aluminum" over the steel).  Crispin says the efficiency should be strongly
> modified by the materials and weight differences - which I can see makes
> sense.
>
>
>
>    My problem is that playing around with Dale's stated power levels ("*The
> power input to the regular pot was 1128 Watts, while that of the finned pot
> 1227 Watts, or 1.088 times as much."), * I can't see from the given data,
> how Dale got those power numbers.  I think there should have been some
> water evaporated, but none is stated.  Did the 700 watt number come in some
> way?
>
>
>
>    So,  Dale, can you show the computations you used to get 1128 and
> 1227.? Adding in the specific heat of the pots (if you didn't - and you
> might have) should help with better understanding both this geometry and
> the importance of including what Crispin wants to include.
>
>
>
> Ron
>
>
>
>
>
>
>
>
>
> On Nov 18, 2013, at 4:57 PM, Crispin Pemberton-Pigott <
> crispinpigott at gmail.com> wrote:
>
>
>
> Dear Dale
>
>
>
> What a welcome report on a promising technology!
>
>
>
> I have several points that I'd like to raise which probably impact
> materially on your concluding numbers.
>
>
>
> I am happy to see at the end a discussion of the thermal mass of the pots
> and the fact they have different materials and different masses. Because
> the tests were conducted to check the heat transfer efficiency and the
> overall fuel consumption (two different metrics) at high and low power
> (again, two different metrics) I feel it is important to put the thermal
> mass in context at the beginning then move to the other points.
>
>
>
> The British, Indian, SeTAR and Indonesian heat transfer efficiency tests
> all consider the mass of the pot in the calculation. There may be many
> others - I have not read them all, of course. I would like to investigate
> the implications of this.
>
>
>
> The work done heating the water (and the pot) is measured to the boiling
> point and includes heating the thermal mass of the water and the pot
> together. At the very end you mention the difference in in energy being
> 130,000 for the aluminum and 26,000 for the stainless steel pots. This
> 104,000 Joule difference should be applied to the portion of the test that
> involves changing the temperature, not the whole test because most of the
> time, there is no change in temperature.
>
>
>
> The answers sought related to portions of the test, which are separately
> reported (good). If we take the change in temperature to be 80° C then the
> energy needed to heat the water (calculated on the same basis as the energy
> needed to heat the pot) is:
>
>
>
> 5000 g x 4.186 x 80° = 1,674,400 J
>
>
>
> The pots used respectively 26,000 and 130,000 (from your calculation)
>
>
>
> Thus the two tests require 1,700,400 and 1,804,400 respectively for a
> difference of 1.061 in the heating work done. This means the improved pot
> was required to (and did) absorb 6.1% more heat during that portion of the
> test. Once the pot is hot, the impact of the pot mass disappears because
> the temperature is pretty much constant.
>
>
>
> Because the pot mass was not considered in your calculation, the
> 'additional heat gained' number (the claim that all things considered, it
> gains heat more efficiently) drops from 16.1% to about 10%
>
>
>
> 10/16.1 = 0.62, 1-0.62 = 0.38 = 38% under-reported performance
>
>
>
> I think recalculating it to include the pot mass would materially affect
> the conclusions - i.e. that the difference in the calculated result is
> significant with a high degree of confidence.
>
>
>
> With respect to the determination of thermal efficiency at low power, the
> things being measured - missing mass of water and energy consumption - are
> not strongly correlated because, as you clearly explained, the losses of
> heat from the pot by routes *other than evaporating water* are large
> compared with the energy used for evaporating water. Very small changes in
> the local circumstances strongly affect the calculated result.
>
>
>
> For this reason, there was some time ago a general agreement that
> 'simmering efficiency' is not really a helpful indicator because the
> calculated efficiency of a perfect simmer is 0% which is counter-intuitive
> to the claim of the method applied. If you changed the low power fuel burn
> rate, you will get a different low power efficiency at each power setting
> because it is a method that does not actually report the low power heat
> transfer efficiency (or the fuel efficiency).
>
>
>
> I predict, based on your numbers, that if you were to test the same pots
> using cold water on a low power flame, the heat gained by the finned pot
> would be of a similar order of magnitude larger than the standard pot as is
> shown above, i.e. the difference between 10 and 16.1.
>
>
>
> The work done by the stove in heating the water can most accurately be
> measured when the water is not boiling for all the reasons you stated about
> conductive, convective and radiative losses. As we are testing the pot, not
> the stove or the fuel, it will be most accurate if the water and pot are
> heated from some temperature above ambient such as 30° (to ensure that the
> heat gain rate is continuous and stable) to about 70° above which point
> some evaporation can be expected, complicating the calculation and
> introducing the relative imprecision caused by a changing mass v.s. a
> changing temperature. Heat gain assessed by ΔT is about 500 times more
> accurate than assessing it by ΔM.
>
>
>
> The presence of a lid ensures that the heat gained is collected and not
> lost to radiation or small amounts of water evaporating. The result, the
> temperature rise of a 20° pot from 30° to 70°, is a very good reflection of
> the gained by the pot and virtually eliminates errors.
>
>
>
> I would be really interested to see the difference between these two
> methods reported for that very same pot, taking your set of experiments as
> a baseline. I predict that the improvement in heat gain, calculated from
> 30° to 70° and taking into consideration the pot material and mass, will
> show an improvement of about 16% for a steady state fire of any magnitude
> that you used.
>
>
>
> Where my estimate will be wrong is the low power comparison because the
> baseline is not really a measure of heat transfer efficiency, but my
> estimate not it will not be as wrong as the baseline number.
>
>
>
> As the finned pot is claimed to be for cooking with gas (as I understand
> it) only two need be need be performed for high and again for low power
> (one for each pot type).
>
>
>
> Because the heat transfer efficiency is not dependent on the mass of water
> in the pot, the water does not need to be exactly 5000 g if the pot mass is
> considered. This is important for testers to realise.  This
> mass-independence was recently confirmed again by students at the China
> Agricultural University to a high degree of precision (four nines) across a
> wide range of 'pot fullness'.
>
>
>
> I find this knowledge really helpful for comparing stoves that do not deal
> well with such a large pot. Putting in 4 litres of 5, or 6 would not change
> the calculated heat transfer efficiency because it doesn't measurably vary.
> But the pot mass must be considered if there is a change in water
> temperature.
>
>
>
> If there are other experimenters in Stove Land who have finned pots it
> would be great to hear from them as well, comparing not only the different
> appliances, but the different calculation methods.
>
>
>
> Best regards
>
> Crispin
>
>
>
>
>
> A few months ago we had a discussion of Cajun Rocket Pots, a series of
> pots with heat transfer fins on the bottom meant for cooking seafood in the
> Southern US.  Their claim was that their pots reduce fuel use by 50% and
> reduce time to boil considerably.  (The name "Rocket Pot" has nothing to do
> with the rocket stove.)  I gave the opinion that their design was excellent
> and that it would revolutionize our cookstove work.  All we had to do was
> test it on some stoves of the type we use and confirm that it works.
>
>
>
> Alas, reality interfered.    I got one of their pots, the 8 quart size.
> This is their smallest size and is appropriate for a 5 liter water boiling
> test.  The finned pot performed only marginally better than a regular pot
> of the same size, typically by about 10%.  Very disappointing.  It's
> possible that for certain types of stoves with certain shapes of gas
> burners the pot really does perform well, but it did not perform
> particularly well on any of the stoves I tested.
>
>
>
> I've attached a report with the test details of a finned and a regular pot
> being tested on 7 different stoves.  Some stoves gave better results than
> others, but the 10% improvement is a typical number.
>
>
>
> Dale Andreatta
>
> <Cajun Rocket Pot
> Report.pdf>_______________________________________________
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