[Stoves] Airflow For Biomass Fired Appliances- Natural Draft Stoves

[Lanny Henson]

I am going through my stove notes while I am sitting here! 

It will be a couple of weeks before I can work, so you may have to suffer my stove topics a little longer.  Smile

 

I am putting together some thoughts about natural draft and combustion airflow. 

Do you see anything that needs to be corrected or expanded on, or added? Other than grammar/spelling.

I would like to avoid words and terms that can not be understood by the average person or someone not good with English.

Your criticisms and comments are appreciated.



 Airflow For Biomass Fired Appliances- Natural Draft Stoves.

Good combustion airflow is important for natural draft cookers, but the air pressure from natural draft is very low. 

Restrictive airflow paths in a stove can be a problem for air volume and for getting combustion air to the best place for clean combustion.

 

Draft and airflow:

Draft is important for natural airflow:

Draft is like reverse gravity, hot air flows up.

Heat powers the draft, the more heat, the more air flow.

Draft height effects air flow. 

Heat can be siphoned or moved around a cooker like water can be siphoned, if there no leaks in the stove.

 

Restriction reduces airflow for natural draft designs:

The more turns, or changes in direction you have, the more restriction you get.

Quicker the turn, more the restriction.

Smaller the holes, more the restriction.

Chaotic air flow creates more restriction.

Losing the momentum of the airflow through the system can reduce airflow.

Restriction can increase air velocity which can be good at the right place.

Restriction of the air flow can be used to limit excess air.

Restriction of combustion air can be used to control the fire/heat.

 

Things that help airflow:

Fewer changes of direction. 

Longer turn radius for the air flow

Pathways that are less restrictive than small holes.

An orderly flow path with less turbulence helps air flow

Momentum or a continuous flow without starts and stops helps airflow.

 

Air flow and clean combustion:

The flow path needs to lead to the place where the combustion air can best be used.

There should be enough velocity to mix the gases and possibly blast fuel. 

The combustion air needs to be focused on the combustion zone in a way that shortens the flame height. More like the way a TLUD with a fan works. 

Flames should be complete before touching a surface, like a pot or a griddle. 

 

Air flow and excess air: 

Excess air needs to be minimized; 

Unnecessary air dilutes the heat and carries the heat away with the exhaust.

 

Air flow and “radiant view”:

Air flow can be used to shorten flame height which puts the fire closer, where there can be a larger radiant view.

The larger the “radiant view” of the pot to the radiant heat source the better. 

 

Air flow and Stove construction:

Focused airflow can shorten flame height so you can use a shorter stove body, less materials to build the stove, and less materials to soak up the heat, and less surface area to loose heat.

 

Lanny Henson

Criticism is the friend of correctness and the enemy of foolishness -LH
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