Droplet entrainment and size distributions from flow separation over a melting paraffin slab

Abstract In this study, the effects of separated flow over a melting paraffin slab on atomization is considered. Experiments are conducted using an optical chamber with a paraffin wax slab exposed to high shear flows of 71–234 kg/m $$^2-$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>2</mml:mn> </mml:mmultiscripts> <mml:mo>-</mml:mo> </mml:mrow> </mml:math> s with non-vitiated heated air at 84–199 $$^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> </mml:math> C. The formation of a lobe structure and leading edge instability responsible for wax atomization is imaged and quantified. The lobe height and receding angle are measured, and a simplified theory is developed to predict the steady-state shape using a sinusoidal profile. A Weber number of the leading edge is defined (We $$_\textrm{LE}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mtext>LE</mml:mtext> <mml:mrow/> </mml:mmultiscripts> </mml:math> ) to non-dimensionalize and correlate the experimental data to the theory. A linear correlation is observed with an $$R^2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>R</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:math> of 0.94 between the shear correction factor and We $$_\textrm{LE}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mtext>LE</mml:mtext> <mml:mrow/> </mml:mmultiscripts> </mml:math> . The overall agreement between theory and measurements is good for the lobe height and width. Measurements of entrainment from the lobe account for $$\approx 20\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>≈</mml:mo> <mml:mn>20</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> of the total mass loss. The size of the droplets entrained from the leading edge are recorded and normalized. Droplet size distributions for varying air fluxes and temperature are shown to collapse to the same distribution when normalized using their z-scores.