Heat and mass transfer of combusting monodisperse droplets in a linear stream

Abstract

Heat and mass transfer phenomena in fuel sprays is a key issue in the field of the design of the combustion chambers where the fuel is injected on a liquid form. The development and validation of new physical models related to heat transfer and evaporation in sprays requires reliable experimental data. This paper reports on an experimental study of the energy budget, i.e. internal flux, evaporation flux and convective heat flux for monodisperse combusting droplets in linear stream. The evaporation flux is characterized by the measurement of the droplet size reduction by the phase Doppler technique, and the droplet mean temperature, required for the internal and convective heat flux evaluation, is determined by two-color, laser-induced fluorescence. The Nusselt and Sherwood numbers are evaluated from the heat and mass fluxes estimation, as a function of the inter-droplet distance. The results are compared to physical models available in the literature, for moving, evaporating and isolated droplets. A correction factor of the isolated droplet model, taking into account drop-drop interaction on the Sherwood and Nusselt numbers, is proposed.

Characterization of the evaporation of interacting droplets using combined optical techniques

“…They demonstrated that the reduction in the heat and mass transfers can differ between the liquid fuels even at identical distance parameters and Reynolds numbers. They also observed significantly greater reductions than those reported by Castanet et al (2005) for combusting droplets. These differences were attributed to the fuel volatility.…”

“…Important parameters such as the distance between the droplets are modified in order to characterize their influence on the droplet evaporation. Monodisperse droplet streams have been used in previous studies of droplet evaporation (Castanet et al 2005(Castanet et al , 2011Deprédurand et al 2010;Virepinte et al 2000). These studies emphasized the role of the dimensionless spacing parameter C, defined as the ratio between the droplet spacing L and the droplet size d. For low values of C, the heating and evaporation rates are reduced in comparison with the isolated droplet whose evolution can be predicted using classical models (Abramzon and Sirignano 1989).…”

“…Comparisons reveal that the inter-droplet For rapidly vaporizing droplets, it can be assumed that the vapor released by the drops is transported in the vicinity of neighbor droplets reducing the gradients of vapor concentration near their surface and thus their vaporization rate. Castanet et al (2005) studied the evaporation of ethanol droplet streams in a combusting flow. They observed significant reductions in the heat and mass transfer rates for C lower than 9.…”

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

“…This function depends on both fluorescent dye and solvent of interest. An interesting side consequence of this model concerns the case of evaporating or combusting droplets (Castanet et al 2003 andCastanet et al 2005). In these cases, the droplets diameter decreases continuously due to the evaporation of the volatile fuel.…”

Monodisperse monocomponent fuel droplet heating and evaporation

“…[4]). This assumption contradicts direct measurements of the temperature distribution inside droplets [5,6]. Bertoli and na Migliaccio [7] were perhaps the first to draw attention to the fact that taking into account the temperature gradient inside droplets can considerably increase the accuracy of the CFD modelling of combustion processes in Diesel engines.…”