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. < [email protected]> 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:[email protected]] > *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 < > [email protected]> 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>_______________________________________________ > Stoves mailing list > > to Send a Message to the list, use the email address > [email protected] > > to UNSUBSCRIBE or Change your List Settings use the web page > > http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org > > for more Biomass Cooking Stoves, News and Information see our web site: > http://stoves.bioenergylists.org/ > > > > _______________________________________________ > Stoves mailing list > > to Send a Message to the list, use the email address > [email protected] > > to UNSUBSCRIBE or Change your List Settings use the web page > > http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org > > for more Biomass Cooking Stoves, News and Information see our web site: > http://stoves.bioenergylists.org/ > > >
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