A simplified model for understanding natural convection driven biomass cooking stoves

Agenbroad, Joshua Nicholas, author
DeFoort, Morgan W., advisor
Willson, Bryan D., advisor
Kirkpatrick, Allan Thomson, committee member
Maloney, Eric D., committee member
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It is estimated that half the world's population cooks over an open biomass fire; improved biomass cooking stove programs have the potential to impact indoor air quality, deforestation, climate change, and quality of life on a global scale. The majority of these cooking stoves operate in a natural convection mode (being driven by chimney effect buoyant fluid forces). Simplified theories for understanding the behavior of this unexpectedly complex combustion system, along with practical engineering tools to inform its design are markedly lacking. A simplified model of the fundamental stove flow physics is developed for predicting bulk flow rate, temperature, and excess air ratio based on stove geometry (chimney height, chimney area, viscous and heat release losses) and the firepower (as established by the stove operator). These parameters are intended to be fundamental inputs for future work understanding and improving biomass cook stove emissions and heat transfer. Experimental validation is performed and the simplified model is shown to be both accurate and applicable to typical stove operation. Carbon monoxide and particulate matter emissions data has been recorded in conjunction with the validation data. The initial results are presented and indicate that the excess air ratio may be a promising tool for reducing carbon monoxide emissions. A dimensionless form of the simplified stove flow model is then developed. This form offers several advantages, including scale similarity and a reduction of independent experimental parameters. Plotting with dimensionless parameters, various stove configurations can be plotted concurrently, and general stove flow behavior common to all natural convection stoves is observed. With a dimensionless firepower axis, emissions trends for both carbon monoxide and particulate matter become apparent, and a region of improved combustion efficiency and lowered emissions is identified.
Department Head: Allan Thomson Kirkpatrick.
2010 Summer.
Includes bibliographical references (pages 82-84).
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