Study of splash characteristics and spreading mechanism of liquid droplets impacting walls at low temperature

The phenomenon of droplets impacting on the cold wall is one of the key factors leading to the deterioration of aircraft wing icing, wire icing and cold start of internal combustion engine. Droplet splashing and spreading characteristics are the main causes of the above problems. High-speed photography was used to study the splashing and spreading characteristics of n-dodecane droplets striking aluminium plates at different temperatures. The results show that as the wall temperature decreased (20 ℃ to −40 ℃) the droplet fragmentation threshold is significantly reduced, the secondary droplet diameter and number increase significantly, and the spreading speed and maximum spreading distance of the attached liquid film decrease significantly. In this study, a new dimensionless spreading coefficient (β_T = (D/D₀)/Re_T^0.07) and a new spreading model (β_T = 1.76τ^0.5) were constructed for the kinematic characteristics of the fast spreading phase of the liquid film attached to the low temperature wall, considering the effect of wall temperature on the viscous forces. The spreading model not only enables an accurate description of the liquid film spreading process under different insertion conditions and wall temperatures, but also widens the range of application of the model from 0.1 ≤ τ ≤ 1.0 to 0.1 ≤ τ ≤ 1.5, allowing the resulting low temperature spreading model to accurately describe changes in the spreading pattern of the liquid film over a longer period of time.