A generalized model for hydrocarbon drops spreading on a horizontal smooth solid surface

Hydrocarbon drops impacting on a flat solid surface were experimentally and computationally studied to identify the key issues in the dynamics of drop spreading. Three hydrocarbon liquids were tested: diesel, methanol and glycerin. The evolutions of dynamic contact angle and spreading diameter were measured at each time step after impact from the recorded images. Two distinguishable regimes were observed during the evolutions: an initial kinetic regime followed by a spreading regime. While the kinetic regime could be accurately predicted with a single static contact angle (SCA) model, in this work, a general empirical expression (in terms of the Ohnesorge number) was constructed that accurately describe the spreading regime. The transition threshold, from the kinetic regime to the spreading regime, follows with a power law, changing as a function of Reynolds number.

In addition to the experimental investigations, the drop spreading process was studied numerically with a volume-of-fluid (VOF) approach. Based on these investigations, a new combined static contact angle-dynamic contact angle (SCA-DCA) model was proposed and applied to compute the hydrocarbon drop spreading process. The predicted time-dependent drop shapes agree well, within 5% of both previously published results and the experimental data presented here, while previous models showed at least a 10% deviation from the experiments. This proposed model also avoids the requirement for experimental measurement with specific fluids and only requires the general fluid properties. An added benefit of this methodology is that the computational cost is greatly reduced compared with the existing (full DCA-based) models.

To broaden the applicable range of this new model, water drop spreading on the solid surface was also studied. It was concluded that this model could predict the liquid drop spreading on a flat smooth solid surface (clean glass) with the range of Oh=O(0.001)-O(0.1), We=O(0.1)-O(100), Re=O(10)-O(1000).