Mathematical modelling of biomass briquettes combustion : a coupled heat and mass transfer with reaction kinetics.

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dc.contributor.authorWaniale, Buruhani Two
dc.date.accessioned2026-09-23T11:27:52Z
dc.date.available2026-09-23T11:27:52Z
dc.date.issued2026
dc.descriptionDissertation
dc.description.abstractBiomass briquettes uptake across the global is still low stemming from inefficient household combustion performance resulting into high emissions. Moreover, the producers lack validated predictive tools that could curb the vice. This study developed a multiphysics optimization framework to maximize the net energy output of biomass briquette combustion using agricultural residue streams representative of East Africa including sugarcane bagasse, maize cobs, and coffee husks. The methodology integrated three sequential research phases; experimental laboratory characterization, a 2D axisymmetric coupled Computational Fluid Dynamics model and optimization framework based on a 5-factor Central Composite Design (CCD) controlled 50 forward COMSOL simulations over a comprehensive operational space spanning moisture content (wm), equivalence ratio (ϕ), air velocity (uin), geometric aspect ratio (H/D), and compaction density (ρb). Ordinary least squares regression was used to develop quadratic surrogate models with high predictive accuracy (R2 ≥ 0.987). Through incorporation with Method of Moving Asymptotes (MMA) optimization framework, energy output was maximized while meeting the tight engineering constraints for peak temperatures (≤ 1100 ◦C), carbon monoxide emissions (≤ 300 ppm), and complete burnout (≥ 85%). The global optimization solution yielded a substantial 49.2% to 53.3% improvement in net thermal output over baseline runs. The results demonstrate that strict fuel pre-drying (w ∗ m = 7.8% − 9.2%) combined with targeted air delivery (ϕ ∗ = 0.86 − 0.90) represents an optimal operating threshold, providing direct, quantitative design parameters for low emission cookstoves and sustainable biomass deployment. Therefore GVEP-type designers should target a chimney of height 150mm, ϕ ∗ = 0.88 while further research should test these optimal conditions in actual Ugandan households under variable ambient conditions (altitude, Humidity, user behaviors etc). Keywords: Emissions, Cooking Stove, COMSOL Multiphysics, Response Surface Methodology, Method of Moving Asymptotes, Thermal Efficiency.
dc.description.sponsorshipDr. Asaph Keikara Muhumuza ; Dr. Fulgensia Kamugisha Mbabazi ; Busitema University
dc.identifier.citationWaniale, B. T. (2026). Mathematical modelling of biomass briquettes combustion : a coupled heat and mass transfer with reaction kinetics. [Unpublished dissertation]. Busitema University.
dc.identifier.urihttps://bdears.busitema.ac.ug/handle/123456789/9624
dc.language.isoen
dc.publisherBusitema University
dc.titleMathematical modelling of biomass briquettes combustion : a coupled heat and mass transfer with reaction kinetics.
dc.typeOther
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