Combustion simulation in a differentially heated diffuser under free convection

The present work is aimed to explore combustion in a vertical diffuser with an emphasis on the buoyancy-induced nature of the flow. This combustion problem is similar to the combustion of pyrolysis gases in an annular vertical diffuser which is widely used in rural areas for cooking. The analysis of the problem is complicated owing to the coupling amongst natural convection flow, heat transfer and combustion. A simple finite reaction rate model for a single component fuel is presented for the combustion process. Then, the fuel is taken to be a mixture of combustible gases and an Arrhenius-type single step reaction is assumed between each of the combustible gases and oxygen. In each stage of modelling, temperature profiles are generated for various tube wall temperatures and fuel inflow rates. Results indicate that the maximum flame temperature is located close to the radial diffuser. The flame tends to move away from the wall with higher volatiles flow rate and higher wall temperatures also. It was also seen that maximum flame temperature increases with increase in tube wall temperature and power input, maximum flame temperature region spread in radial diffuser. Heat transfer efficiency increase with increase in power input.