On Drag of Evaporating Liquid Droplets

Abstract

Abstract —Drag data of water, methanol, heptane and benzene droplets are reported here. This data together with the data of Eisenklam et al. cover the entire range of Reynolds numbers from 1 to 2000 and mass transfer numbers from 0 to 3. The present study shows that the drag coefficients as a function of Reynolds numbers correlate well with the “standard drag” curve provided the characteristic density is the free stream density and the characteristic viscosity coefficient is μ r (Tr ). The basis for the choice of these two characteristic properties is discussed. The present correlation is insensitive to the mass transfer number. This suggests that mass efflux has little effect on drag of evaporating droplets. Present study indicates that for the determination of the drag coefficient of any evaporative droplet at quasisteady state, one needs only to know the wet bulb temperature as a function of free stream temperature. This information is sufficient to calculate μ r (Tr ). The “standard drag” curve can then be applied to determine the drag coefficient.