A COMPUTATIONAL STUDY OF THE EVAPORATION CHARACTERISTICS OF AN AIR- BLAST ATOMIZED, KEROSENE SPRAY IN POROUS MEDIA

摘要

The evaporation characteristics of an air-blast atomized kerosene spray in porous media in a 2D-axisymmetric coflow environment were studied numerically. A swirling primary air stream with varying intensity was used to aid the atomization process. The effects of non-Darcy flow in porous medium were modeled using a modified form of Ergun equation. Local thermal equilibrium between the fluid mixture and porous medium was assumed. Conductive and transient heat flux terms in the energy equation were modified to include the effective thermal conductivity and thermal inertia of the solid region respectively. The effective thermal conductivity was defined as the volumetric average between solid and fluid media. First, the temperature characteristics of the porous medium, arising from different source terms, were obtained. Complete vaporization of kerosene was achieved when the maximum temperature of the porous medium was at 590 K. The effects of porous medium temperature, primary air swirl number, fuel flow rate, and secondary (coflow) air inlet temperature on vaporization were analyzed. For all cases, kerosene vapor concentration profiles at five different axial locations in the domain (0.08, 0.12, 0.13, 0.14, and 0.19 m from the nozzle) were obtained. An increase in secondary air inlet temperature from 373 K to 473 K increased the completeness of evaporation from 94% to 97%. When the swirl number was increased from 0.14 to 0.34, the peak vapor concentration was reduced by 31% and more vapor spread radially. The porous medium temperature was found to be a crucial factor in obtaining the complete vaporization of the spray.