Vaporization of bi-component droplets in a turbulent over-heated flow : Experiments and Numerical Simulation
Résumé
This paper deals with an experimental study of bi-component droplets evaporation in a turbulent over-heated channel flow. Droplets are made of a mixture of n-octane and 3-pentanone (15% in volume). Planar Laser Induced Fluorescence (PLIF) of 3-pentanone is used to derive both concentration of this molecule in liquid and gas phases. Concomitant dispersion of the liquid droplets and evaporation can be clearly observed with a trend to homogenisation of the 3-pentanone vapour in the flowfield due to high turbulence rate, on the order of 40%. The experimental results, in term of concentration of 3-pentanone in both liquid and gas phases have been compared to a simplified numerical simulation based on the discrete component model, taking into account the droplet composition, associated to the isolated droplet model. It appears that the measurements performed on the liquid phase overestimate the calculated evaporation, as the gas phase measurements performed far from the injection point are in correct agreement with the calculations. One of the explanations is that the PLIF CCD camera dynamic is not sufficient to detect simultaneously the biggest and smallest droplets. In the present cases, most of the numerous smallest droplets seem to be ignored by the measurement, which tends to overestimate the droplet evaporation. The second important cause of discrepancy between experimental and numerical results is linked to the strong extinction of the fluorescence signal issuing from the liquid phase, due to the absorption
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