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- The Influence Of Temperature In Regime Transition Boundaries For Single Droplet Impact Upon Heated Liquid FilmsPublication . Mendes, André Filipe Serra Ferreira; Silva, André Resende Rodrigues daThe growing concern with the current rate of consumption of fossil fuels, pollutant emissions and the limitations of the reserves lead to a pursuit of developing more efficient engines with lower emissions and fuel consumption. However, experimental studies of droplets impinging upon a liquid film in similar conditions that would be expected inside a combustion chamber, i.e., simulation of the heating effect by the walls on the liquid film, are required. The subject of droplet impact is relevant to different industries, such as in spray painting, inkjet printing, pesticide dispersion on crops, cooling of hot surfaces such as electronic devices and turbine blades, and of course fuel injection in internal combustion engines. The main goal of this thesis is to evaluate the effect of the temperature of the liquid film on single droplet impact dynamics. The study was focused on assessing the validity and applicability of the current criteria for spread/splash and bubble encapsulation on account that these two phenomena result in greater atomisation of the mixture. The current aviation fuels such as Jet A-1 and NExBTL are multi-component substances, resulting in non-linear evaporation rates since the different fluids that constitute them have different saturation temperatures. As an intermediate step, before the multi-components fuels, simple carbon chains equivalents like N-Heptane and N-Decane were selected. The experimental facility necessary was designed and adapted for the one present in the laboratory to comply with such requirements. The setup included a high-speed camera, a LED array, and a syringe pump connected to a flathead needle, to hold the liquid film a borosilicate container was used and to heat the liquid film an aluminium block with embedded heating cartages. The experiments were conducted at different heights in order to evaluate the effect of the temperature around the selected thresholds. Both phenomena revealed to be affected by the temperature of the liquid film. The phenomenon of bubble encapsulation, for the same height, revealed to happen at higher temperatures but not at room temperature. Although the phenomenon of splash revealed to be similarly affected, it also lead to interesting results near the transition zone, where in a specific range of temperature it was detected a suppressing effect. It was verified that neither of the selected thresholds could corroborate the experimental results obtained. Using this data, an adaptation to the correlation of bubble encapsulation was proposed, although, the same for the spread/splash correlation was not possible.
- Does liquid film temperature affects single drop impact dynamics?Publication . Mendes, André F. S. F.; Vasconcelos, Daniel; Ribeiro, Daniela; Panão, Miguel; Silva, A. R. R.The effect of liquid film dynamics in the hydrodynamics of an isolated drop impact is a complex phenomenon and not fully understood. Therefore, in this work, an experimental setup built to characterize the impact of an isolated droplet on heated and unheated liquid films consists of a heating element made of an aluminum block with resistances to produce several impact conditions. The parametric studies include the drop impact velocity and size for different fluids to evaluate their properties effect on the phenomena. The results were compared with existing thresholds in the literature to evaluate their validity and applicability range. This comparison allows us to assess if temperature causes the limits of the thresholds to change drastically or if its influence is negligible. Regarding IC engines, thresholds like splashing and bubble encapsulation are significant since they influence the atomization of the mixture and, consequently, the pollutant emissions.