Study of soot deposition in flames and its effect on heat transfer to metal surfaces

Soot deposition from hydrocarbon flames was investigated in order to evaluate the evolution of the deposits during the transient process of heating an object that starts with a cold surface and is engulfed in a flame. The study focused on the flame/metal surface interface and the critical issues associated with the specification of the thermal boundaries at this interface, which include the deposition of soot on the metal surface, the chemical and physical properties of the soot deposits and their subsequent effect on heat transfer to the metal surface.;A laboratory-scale device (metallic plates attached to a water-cooled sampling probe) was designed for studying soot deposition in a laminar ethylene-air premixed flame. The metallic plates facilitated the evaluation of the deposition rates and deposit characteristics such as deposit thickness; bulk density; PAH content; deposit morphology; thermo-physical properties such as deposit thermal conductivity (Kdep); and thermal properties such as the temperature of the soot deposits and wall surface temperature of the deposition system, under both water-cooled and uncooled conditions.;A sampling method that minimized the disturbance of the deposit microstructure and the use of the laser flash technique (a nonintrusive technique) were utilized for determining Kdep.;Important differences between water-cooled and uncooled surfaces were observed. Thermophoresis dominates the soot deposition process and enhances higher deposition rates for the water-cooled experiments. The higher presence of condensable material in the deposits for the water-cooled experiments promotes lower deposit thicknesses, larger deposit densities, larger amounts of aromatic and PAH species, different deposit morphologies, and larger thermal conductivities.;The estimation of the thermal properties in combination with other experimentally-measured variables allowed the calculation of the heat flux from the flame to the metal surface, quantification of the heat flux through the deposit and development of a numerical model to describe the thermal interactions between the flame and the deposit/metal surface system under different experimental conditions.