Modelling of bottom-lit down-draft (BLDD) clean-burning coal stove

The use of coal as a household fuel to meet requirements of cooking and heating in low income communities on the South African Highveld results high levels of indoor and ambient air pollution. The combustion of coal is regarded as the largest source of air pollution in Gauteng Province, in terms of resultant human exposure. As part of measures to combat this problem, an innovative clean-burning multi-use (cooking and heating) coal stove has been developed. Incorporating a bottom-lit down-draft (BLDD) design. However, optimising the fundamental design by construction and testing has been a time and resource consuming exercise. In this paper we report on the use of PHOENICS computational fluid dynamics (CFD) software to develop a model for simulating an optimal geometry for the BLDD coal stove, including heat and gas transfer components. We used mass, momentum and energy balances built within PHOENICS software, through FLAIR program (a special-purpose sub-module program of PHOENICS, designed to provide an air-flow and thermal-simulation facility for heating, ventilation and air conditioning systems), to evaluate the basic design in terms of heat distribution from fuel bed to exhaust pipe. As a simplifying assumption for computational efficiency, a model using rectangular conduits was built and validated by comparing the simulations with experimental performance of the stove. This article reports the initial findings of the CFD modelling, involving air flows and temperature profile, assuming a constant heat source located in the combustion chamber. Validation of the model will lead to an accelerated design cycle for reaching a design solution for optimised thermal (cooking) performance and reduced pollution emissions.