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Abstract
The combustion of a fuel droplet in a mixed convective environment has been simulated both theoretically and experimentally. In the theoretical model, the flow and transport equations have been solved subject to the assumptions of constant properties (except for density) and infinite rate kinetics, using the finite element method. The gas density has been treated as a variable, only to determine the buoyancy force contribution, and it has been evaluated assuming an ideal gas mixture. A porous-sphere facility has been employed for simulating the burning characteristics of a fuel droplet experimentally. The effects of airflow rate and droplet size have been studied for both upward and downward airflow configurations.
Theoretical predictions for the mass burning rate and flame shape are in excellent agreement with the experimental results of the present study and also those reported in the literature. For upward airflow configuration, the mass burning rate is under-predicted by 15 to 20 percent when buoyancy effects are neglected. For downward airflow configuration, the flame shape is similar to the case of upward airflow for low air velocities. For higher downward air velocities, a flattened cylindrical flume front is obtained due to the opposing natural convection and forced convection flow fields, which has been predicted successfully. A detailed parametric study involving the variation of Reynolds number, ambient temperature and ambient oxygen concentration has also been carried out.
