[Stoves] Improving Thermal Efficiency (TARP-VE)

[rogerio carneiro de miranda]

Thanks Dean.

These are helpful tips.

Rogério

2012/5/30 Dean Still <deankstill at gmail.com>

>  Hi All:
>
>
> This winter the new International Working Agreement (IWA) was ratified in
> The Hague. Four health based tiers divide stove performance. A top rated
> Tier 4 stove (PM and CO) without a chimney is estimated to protect human
> health in a small kitchen with 15 air exchanges per hour. Carbon Monoxide
> isn’t as bad as Particulate matter when inhaled so it’s a lot easier to get
> a 4 (an “A”) for CO but only super clean stoves can make Tier 4 for high
> power PM. (Low power PM is easier.)
>
>
>
> Most improved stoves that we have tested recently get 2’s and 3’s for PM
> (a little bit of PM causes serious respiratory problems) but even
> relatively ‘normal improved' stoves can get into the 4 category for CO.
> It’s also possible for stoves to get a “4” for thermal efficiency. The
> stove has to score above 45%. We used to think that this kind of score was
> almost impossible to achieve. But now the understanding of heat transfer
> efficiency has been ratcheted up a notch.
>
>
>
>  Here’s how we try get a “4” on the IWA report card for thermal efficiency:
>
>
>
> We use an acronym (TARP-VE) to remind us of the most important variables
> when designing a stove that uses the least fuel to boil and simmer water.
>
>
>
> 1.)    *Temperature*: increase as much as possible the temperature of the
> gases/flames touching the pot.
>
> 2.)    *Area*: increase as much as possible the area of the pot touched
> by the gases/flames.
>
> 3.)    *Radiation*: Don’t forget how powerful radiation is! While Rocket
> type stoves depend on optimizing convection, if the pot can be exposed to a
> hot radiating surface, water will boil a lot faster.
>
> 4.)    *Proximity*: Force the hot gases into narrow channels as close to
> the pot or griddle without decreasing the velocity of the flow.
>
>        5.) *Velocity*: Slowing the hot gases decreases the heat transfer
> efficiency. Keep the hot gases flowing as fast as possible without
> decreasing the temperature of the gases. Insulate the heat flow path.
>
>        6.) *Evaporation*: We add this reminder that, while a very large
> pot has the advantage that more of the pot is exposed to the heat, a larger
> surface of water is evaporating which can make it difficult to achieve full
> boil. That’s the reason that traditional pots have large bottoms and
> smaller tops.
>
>
>
>  OK, dear friends, that’s our newest check list for making stoves more
> thermally efficient.
>
>
> Best,
>
>
> Dean
>
>
>
>
>
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