New insight into two-color LIF thermometry applied to temperature measurements of droplets

Abstract

To cite this version:Alexandre Labergue, Valérie Deprédurand, Alain Delconte, Guillaume Castanet, Fabrice Lemoine. New insight into two-color LIF thermometry applied to temperature measurements of droplets. Experiments in Fluids, Springer Verlag (Germany), 2010, 49 (2), pp.547 -556. <10.1007/s00348-010-0828-x>. <hal-01570426>New insight into two-color LIF thermometry applied to temperature measurements of dropletsAbstract When laser-induced fluorescence of droplets is used for measurements such as droplet temperature, a new dependence of the droplet size on the spectral distribution of fluorescence has been highlighted. The two-color laserinduced fluorescence technique applied to droplet temperature measurement requires a single fluorescent tracer and two spectral bands of detection for which the temperature sensitivity is different. Generally, the ratio of the intensities measured on each of the spectral bands of detection is assumed to be only temperature dependent. However, droplet dependence on diameter is also likely to influence the intensities ratio. This study provides some illustrations of the phenomenon, first on sprays with different mean statistical diameters and secondly on single droplets, for two temperature-sensitive fluorescent tracers in their solvents: sulforhodamine B dissolved in water and pyrromethene 597-8C9 dissolved in n-decane.

Study of the droplet size effect coupled with the laser light scattering in sprays for two-color LIF thermometry measurements

“…This effect corresponds to a significant distortion of the fluorescence spectrum. The deviation from the previous model is more important when the droplets are small, typically under 100 lm (Labergue et al 2010). This effect was reported for two fluorescent tracers (sulforhodamine B and pyrrométhène 597-C8) dissolved in two different solvents (water and n-decane, respectively).…”

“…Moreover, it appears clearly that small droplets are more frequent in spray (1) than in spray (2). The mean -6 mol l -1 (Labergue et al 2010) diameter D 10 is about 25 lm for spray (1) and 200 lm for spray (2). From Fig.…”

“…This effect was reported for two fluorescent tracers (sulforhodamine B and pyrrométhène 597-C8) dissolved in two different solvents (water and n-decane, respectively). Figure 1 is extracted from Labergue et al (2010): it depicts the evolutions of the fluorescence ratio of single calibrated droplets normalized by a reference taken in a cell, under isothermal conditions in the case of sulforhodamine B dissolved in water (C = 5 9 10 -6 mol l -1 ). A significant increase of the fluorescence ratio is observed when decreasing the droplet diameter, otherwise the normalized fluorescence ratio tends to 1 for the large droplets.…”

“…A significant increase of the fluorescence ratio is observed when decreasing the droplet diameter, otherwise the normalized fluorescence ratio tends to 1 for the large droplets. To account for the effect of the droplet size on the fluorescence ratio, an empirical function g 12 (D) is added (Labergue et al 2010 (1), is a full cone spray generated by a Danfoss Ò swirled nozzle commonly used for burners. The injection pressure varies from 1 to 7 bars, and the liquid flow rate is of a few l/h.…”

“…The technique was successfully applied to measure the temperature of single evaporating or combusting droplets (Lavieille et al 2001;Castanet et al 2003), but its extension in sprays is not straightforward. In a recent paper, Labergue et al (2010) pointed out that the spectral distribution of the detected fluorescence intensity was modified in a spray compared to a cell. Their results concerning calibrated monodisperse droplets revealed that the fluorescence ratio, in addition to be temperature sensitive, is also affected by a residual dependence on the droplet diameter.…”