Effect of liquid property and flow conditions on entrainment and mean droplet diameter in case of two-phase air/ viscous liquid free jets

Measurements by using two-dimensional Phase Doppler Anemometer in free jet flows with several nozzle conditions show that the entrainment process is enhanced when increasing only the liquid viscosity, if any effect due to the in parallel raise of the static surface tension is disregarded. The so called two-phase entrainment coefficient starting from zero develops in the region of flow establishment and approaches a self constituting value in the similarity region of the jet. With higher liquid viscosity, the Ohnesorge number substantially increases due to the reducing of the size of primary and satellite droplets. The physical reason is that the higher viscous forces act on the interface in the sense to damp the rate of droplet distortions and to stabilize the surface tension perturbations. Hence, the increment of the jet breakup length and eventually the droplets formation becomes more pronounced. The mean droplet diameter decreases as well with rising air to liquid phase mass flow ratio for equal total mass flow rates, which is attributed to the higher gas stream impact on the liquid phase. Essentially, the surface tension force interferes with the droplet inertia during the massive interactions between the liquid surface with the gas stream and among the droplets themselves. In horizontal flow, a pertinent gravity effect on the droplets is observed owing to the higher liquid density than that of water.