[Stoves] Bangladesh TLUD (was Re: No subsidies in TLUD char peoduction

Sat Dec 9 09:37:15 CST 2017

Dear Nikhil

Competition on a fuel efficiency basis is independent of what happens within a stove. The statement about heat invested in the stove body is frequently made with the assumption that 'it is bad' to do so. This has been erroneously promoted by certain organisations that insist in their literature that the combustion chamber must be 'insulative' and have a low thermal mass.

Well, only one of 'us' has presented a study comparing light vs heavy with the same design. That was Peter Scott at ETHOS some years ago. He discovered that contrary to the self-proclaimed wisdom of the time , that the heavy, non-insulative combustion chambers consistently out-performed the light ones by about 10% of value for the efficiency metric.

So, here we have Julien discussing the thermal mass of a stove with some jumping in having adopted the incorrect assumption that overall, it is invariably worse to have heat invested in a stove body, without having replicated Peter's experiment.

Observing that heat is invested in a stove body is a trivial exercise. Stating what the overall effect on performance will be is far more difficult. The impact is dependent on multiple factors including the emissivity of the outside surface, and whether there are two or more layers (shells).

To find out which construction or material serves best, we perform efficiency tests and compare numbers. Optimisation is done like that.

Regards
Crispin

Todd:

Didn't you mean exclusive rather than inclusive in "It is not an inclusive to TLUD designs and can be adapted to any stove firebox. "?

Crispin:

If heat loss is insignificant, or only in relation to how it affects the cooking experience, and that heat is stored in the stove for later use, you are basically making my point that competing on fuel efficiency percentages is infantile business.

N

------------------------------------------------------------------------
Nikhil Desai
(US +1) 202 568 5831
Skype: nikhildesai888

On Sat, Dec 9, 2017 at 8:47 AM, Crispin Pemberton-Pigott <crispinpigott at outlook.com<mailto:crispinpigott at outlook.com>> wrote:
Dear Paul and Julien

I am responding to Paul’s comments on Julien’s earlier message.

On Dec 7, 2017, at 6:51 AM, Paul Anderson <psanders at ilstu.edu<mailto:psanders at ilstu.edu>> wrote:

> 1.  The thermal mass is estracting heat, meaning cooler gases inside the chamber, with risk of insufficient temperature for ignition at the top, especially when nearing the end of pyrolysis.

Before anyone worries about heat going into the stove body, please perform the trivial calculation about how much heat we are talking about. Just because heat goes into a stove body does not mean a) it is significant, b) that it happens at a time that affects performance of the cooking experience, c) that it is not returned later in the session (which is cooking behaviour-dependent.) Yes, there is heat invested in the stove and usually it is a loss, but the other features of the stove may not only recover that heat through other energy paths, it may make the stove far more accessible by being cheap and easy to make from local materials.

2.  The concrete (or ceramic) inner cylinder does not have any of the side holes (24 in the metal version).  Such holes allow for some "pilot light" effect after the char level is below a hole.

Dr Nurhuda’s very successful TLUD stove had such pilots sprinkled around the fuel chamber. The Vesto uses three holes only, and the purpose is to maintain pilot lights to ensure the flame never goes out. They are placed in a way that guarantees a small portion of char is burned and there is never a need to relight because of a gust of wind.
Regards
Crispin

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