From: EPA’s Lab Test Results for Household Cookstoves, Jim Jetter, 2012
Since 2012, optimized biomass cook stoves have been tested at ~50% thermal efficiency
The temperature of the hot gases flowing past the surface of the pot is increased by
- Creating as much flame (1,100C) as possible in a low mass, insulated combustion chamber.
- Decreasing the distance between the fire and the pot without making excess smoke.
- Not allowing external air to cool the combustion gasses.
In convective heat transfer, the primary resistance is the surface boundary layer of still air immediately adjacent to a wall.
Increasing Temperatures, increasing exposed Area, increasing Radiation, increasing Velocity in a 6mm to 7mm channel gap (10cm or higher) pot skirt has been shown (up to 5kW firepower) in a 24cm or larger diameter pot to result in ~50% thermal efficiency. Reducing losses from the exterior of the pot skirt with refractory ceramic fiber insulation also increases thermal efficiency.
60% thermal efficiency has been demonstrated in the lab.
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