Mass transfer from liquid fuel droplets in turbulent flow

Abstract

An experimental apparatus and strategy have been developed to investigate the influence of turbulence on the global mass transfer rates from fuel droplets. Heptane and decane droplets suspended in grid-induced turbulent flows have been investigated in the regime where the integral length scales of turbulence are, on average, 5 times larger than the initial droplet diameter. The turbulence intensity has been increased up to 44%. A new mass transfer parameter that distinguishes between the influences of the mean relative velocity and those of turbulence structure has been introduced. Mass transfer from heptane droplets has been found to be insensitive to turbulence. The same turbulence conditions, however, exert a significant influence on the mass transfer from decane droplets. It is shown that the influence of turbulence on the mass transfer from decane droplets can be correlated by a turbulence Reynolds number. The Frössling coefficient is found to increase with the turbulence intensity. The differences in the sensitivity of heptane and decane droplets to the turbulence influence on mass transfer are tentatively explained by introducing a “vaporization Damköhler number.” The present experimental results suggest that turbulence enhances the mass transfer from liquid droplets only for low values of this number.