A NUMERICAL-ANALYSIS OF SINGLE CHAR PARTICLE HEATED BY A LASER

An unsteady state boundary layer model was developed in order to analy se the combustion of single char particles in radiation fields. The mo del is based on the following assumptions, a spherical char particle w ith small diameter is combusted at atmospheric pressure, the temperatu re difference between the surface and the inside of the particle is ne gligible, particle diameter shrinks due to the reaction on the char su rface, the surrounding gas is stagnant, but Stefan flow is taken into consideration and bulk gas flow is neglected. The model predicts the p article temperature increase and the distributions of gas temperature and gas components in the boundary layer. The computed distribution of gas component proves clearly that the reaction rate is mainly control led by oxygen diffusion in the boundary layer except during the initia l heating and reaction. Using the simulation model, the effects of par ticle size, oxygen content in bulk gas and input laser power is discus sed. The results predict that smaller particles heat up taster in init ial heating and higher laser input has the same effect. Further, it is shown that a higher oxygen content raises the sustained combustion te mperature and shortens the combustion period.