Impacts of liquid droplets with another stationary droplet resting on a surface are important basic processes in many applications such as agricultural sprays, spray cooling, and inkjet printing. We investigated the head-on collision of unequal-size droplets of the same liquid on wetting surfaces both experimentally and theoretically at different size ratios and low-impact Weber numbers ( We). A series of high-speed camera images showing representative sequences of collision processes for greatly different size ratios are analyzed. Different collision outcomes such as coalescence, bouncing, and partial-coalescence-partial-bouncing are analyzed thoroughly. Four different stages are identified for characterizing the complete bouncing process during the impact of unequal-size droplets on a solid surface. Subsequently, an analytical model based on energy balance is developed to calculate the maximum spread diameter and restitution coefficient of falling droplets and compared with experimental data, satisfactory qualitative agreements are obtained. Results show that the dimensionless maximum spread diameter of falling droplets depends weakly on We and it is small for a higher size ratio. The restitution coefficient does not change significantly at a higher size ratio at a fixed We despite more viscous dissipation in bigger sessile droplets and it scales with We-1/2.
The isomerization and dissociation reactions of methyl decanoate (MD) radicals were theoretically investigated by using high-level theoretical calculations based on a two-layer ONIOM method, employing the QCISD(T)/CBS method for the high layer and the M06-2X/6-311++G(d,p) method for the low layer.
A two-layer ONIOM[QCISD(T)/CBS:DFT] method was proposed for the high-level single-point energy calculations of large biodiesel molecules and was validated for the hydrogen abstraction reactions of unsaturated methyl esters that are important components of real biodiesel. The reactions under investigation include all the reactions on the potential energy surface of C HCOOCH ( n = 2-5, 17) + H, including the hydrogen abstraction, the hydrogen addition, the isomerization (intramolecular hydrogen shift), and the β-scission reactions. By virtue of the introduced concept of chemically active center, a unified specification of chemically active portion for the ONIOM (ONIOM = our own n-layered integrated molecular orbital and molecular mechanics) method was proposed to account for the additional influence of C═C double bond. The predicted energy barriers and heats of reaction by using the ONIOM method are in very good agreement with those obtained by using the widely accepted high-level QCISD(T)/CBS theory, as verified by the computational deviations being less than 0.15 kcal/mol, for almost all the reaction pathways under investigation. The method provides a computationally accurate and affordable approach to combustion chemists for high-level theoretical chemical kinetics of large biodiesel molecules.
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