Abstract
This paper presents results of single droplet impacts on films of different heights taken using the brightness-based laser-induced fluorescence technique (BB-LIF). The dynamics of drop impingement such as the shape of the cavity and residual film thickness are investigated and analysed with a time resolution of 0.1 ms and spatial resolution of 70 μm. Additionally, a variation of the BB-LIF technique is used to investigate the change in profile of the droplet liquid during the inertial self-similar regime. The results of the analysis show that present models predicting initial development of the cavity show good agreement. Suggested amendments for some of the constants for cavity width and residual film thickness are proposed based on the film thickness that fit better with published data. The development of the profile of the droplet liquid demonstrates that for thin liquid films, the droplet liquid behaviour with strong similarity to droplet impacts on dry solid surfaces. It is noted that for some of the measured parameters, the use of the film height as the length scale gives a better fit.
Highlights
IntroductionAn extensive understanding has been achieved through experimentation and numerical modelling
Droplet impingement on thin liquid films is a common phenomenon in nature as well as in industrial settings that has drawn the attention of researchers for more than a century.Faculty of Engineering, University of Nottingham, Nottingham, UKKutateladze Institute of Thermophysics, Novosibirsk, Russia 3 Novosibirsk State University, Novosibirsk, Russia (Worthington 1877) was one of the first researchers to investigate impacts and studied the behaviour of impinging milk drops using an ingenious method of momentary electric sparks
The dynamics of the drop impact are dependent on the properties of the droplet impact
Summary
An extensive understanding has been achieved through experimentation and numerical modelling. This has accelerated through the development or cheaper high-speed camera (Thoroddsen et al 2008). Even though the works of Worthington were purely driven on intellectual interest, droplet impingement on films is of considerable importance to several industrial applications such as spray coating, 3D printing of mechanical parts, spray cooling, oil and gas transport in pipes and lubrication and heat management of jet engines. This work is motivated by the influence of droplet impact on heat and mass transfer in sheared two-phase flows in process industries and in jet engines
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