Global Temperature Mapping and Crystallization Analysis of Supercooled Water Droplet Freezing Using Luminescent Imaging Technique

A prominent environmental phenomenon that greatly affects many industries including automotive, aeronautics, energy transmission, etc. is icing. One mechanism by which this occurs and plagues our machines and infrastructures that are exposed to the atmosphere is the icing of supercooled water droplets on a surface - either by impact against a surface or spontaneous nucleation and crystallization of a droplet at rest. The process by which nucleation propagates during the liquid-to-solid phase change and the thermodynamic implications in regards to latent heat generation and transfer are not fully understood on the single droplet scale. An attempt to better resolve these unknowns in both spatial and temporal domains has been made here. Previous efforts have implemented a unique temperature sensing technique utilizing luminescent dyes. A thermally sensitive luminescent paint coated onto the surface of interest allows direct mapping of the heat transfer from the supercooled liquid droplet undergoing freezing to the surface. This technique also provides insight into the nucleation propagation speed along the droplet-substrate interface. This, in conjunction with a high-speed color camera and an intense ultraviolet light source are used to accurately resolve the thermal energy within the freezing droplet in both space and time. Synchronization of the thermal data of the droplet with the measurements of transverse heat transfer through the impact surface allow an estimation of heat generation and loss to the environment - key factors in current modelling and simulation efforts used by researchers and industry to predict ice accretion and to better mitigate it.