Analysis and prediction of the gas-liquid interfacial area for droplets impact on solid surfaces

A better understanding of the variation of the gas-liquid interfacial area during droplets impact on solid surfaces in detail is extremely important for process intensification since this can lead to a much-increased efficiency of the heat and mass transfer. At present, experimental observation is the most popular method to investigate the droplet behaviours during the impact of the droplet. However, it is difficult to measure the interfacial areas and observe the transient inner flow field in the droplet. The CFD with VOF model is a powerful and efficient tool for investigating the visual dynamic behaviours, interfacial areas and the detailed inner flow field of droplets. Therefore, effective and efficient CFD models are established to investigate the droplet impact onto solid surfaces through using the VOF model with dynamic contact angle and local grid refinement techniques. The CFD predictions of the dynamic behaviours of the droplets are in reasonable agreement with experimental data over a wide range of surface and liquid properties. The simulation results showed that the gas–liquid interfacial area decreases slightly at the kinematic stage, then increases at the spreading stage, and reaches its maximum at the end of the spreading stage. The hydrophilic surface promotes the increase of gas–liquid interfacial area through releasing the liquid–solid interface energy, while the hydrophobic surface promotes the increase of the gas–liquid interfacial area by promoting droplet breakup. Finally, the energy conversion of the droplet impact on the solid surface is analysed, and a new correlation for predicting the maximum gas–liquid interfacial area of the droplet is proposed.