Concurrent evaporating spray jets in dilute gas-solid pipe flows

This study is aimed at better understanding the phase interactions and microstructures of concurrent evaporating spray jets in gas-solid pipe flows. A study that combined experiments, analytical modeling and numerical simulation has been carried out to explore the unique characteristics of phase mixing and spray evaporation. A continuous circulating gas-solids suspension flow apparatus has been constructed and a concentric liquid nitrogen spray jet was concurrently introduced into the fully developed gas-solids flow. The spray structure was investigated based on both laser-assisted flow visualization and the temperature measurements along the axis using a thermocouple array. In order to interpret the experimental findings and go beyond the experiment limits, modeling approaches were developed, including analytical models and full-field numerical simulations. The analytical model accounts for turbulent phase transfer and interactions between the spray and the ambient flow and successfully reveals basic characteristic phenomena such as the shortening of the spray penetration, evaporation induced temperature reduction and evaporation-induced gas acceleration. The numerical simulation, based on a hybrid Eulerian-Lagrangian method, yields the local phase interactions, evaporation rate, and phase distributions that would otherwise be difficult to determine.;In this study, the proposed thermocouple measurement method can quantitatively determine the dense spray region for sprays (using temperature jump characteristics) in dense gas-solid flows and in dilute gas-solid suspensions with indistinguishable droplets and solids particles, which was further interpreted by the proposed mechanistic model. A systematic investigation is carried out for the shortening effect of solids loading on the spray evaporation length. The evaporation length is found to decrease monotonically and asymptotically when the solid concentration is increased. Within the range of this investigation, the most sensitive range of shortening effect of solids loading occurs within 0.5%, whereas the shortening effect becomes relatively insensitive beyond this point. The numerical simulation revealed the strong non-uniformity in phase distributions. An interesting finding is the existence of similarity in gas velocity profile in the main spray region. The dimensionless velocity distributions are not only similar but also match the Schlichting formula or "the Law of 3/2" of single-phase jets. It appears that the similarity model for one phase jet may be extended to three-phase jets with strong droplet evaporation.