Abstract
The effect of varying the film temperature from 15C to 60 C is investigated using high speed video imaging. It is demonstrated that increasing the temperature difference between the droplet and film liquid changes the size and frequency of the secondary droplets. The impact can be split into three regimes. In the crater expansion regime, the crater follows a self-similar behaviour. In the second stage, the crater becomes deeper and wider at higher temperatures possibly due to decrease in the viscosity or surface tension. It is seen that the crater collapse is less dependent on the temperature and occurs at fixed time for a particular Webber number.
Highlights
The phenomenon of droplets impacting onto both liquid and solid surfaces has been of great interest since the early 1900s, one of the first to investigate the characteristics of splashing being [1]
At 50 C it is clear that the secondary droplets generated from the jet formed after collapse of the impact crater are smaller and more frequent
This might be expected since the surface tension and viscosity of the film liquid are decreased by an increase in temperature
Summary
The phenomenon of droplets impacting onto both liquid and solid surfaces has been of great interest since the early 1900s, one of the first to investigate the characteristics of splashing being [1]. Within internal combustion engines the lubricating oil is sprayed from the rotating parts onto the interior walls, quickly creating an oil film. The following oil droplets will inevitably splash when impacting onto the film, creating secondary drops. Minimising these secondary drops is of great importance to engine manufacturers as they are believed to reduce efficiency. This study is relevant to industry by developing an understanding to how temperature may affect the outcome of droplet impact onto liquid films. There are few studies on droplets of different temperature to the film [6, 7]. This work is part of an experimental study to provide data for comparison with models to confirm or deny if they are still valid in the case where the film liquid has different properties
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