Measurements of gas entrainment in evaporating spray jets

The jet-induced entrainment can be significantly different for jets with evaporating sprays, compared to those of single-phase jets. The heat and mass transfer properties of a liquid jet could be dominate factors governing the nature of the jet. These factors are mainly associated with the amount of mass of the surrounding air induced into the jet. In this study, we have experimentally investigated the air entrainment by a liquid nitrogen spray jet as well as that by a cold nitrogen gas jet near the liquid nitrogen temperature. An oxygen concentration measurement system was used to determine the local oxygen concentration that is purely due to the jet entrainment while the spray jet velocity was determined using a Laser Doppler Velocimetry system Temperature profiles were also monitored using a mini-sized thermocouple on a traverse. Entrainment velocities as well as mass entrainment rate of surrounding air into the jet were calculated by integrating the product of concentration and velocity within the spray jet boundary. Our results indicate that the jet similarity criterion still holds for two-phase evaporating liquid spray jets for circular nozzles. Experimental results of the entrainment rate and similarity of the single-phase jets were quantitatively compared against those from the classical jet theories. It is found that the mass flow rate of air entrained is significantly increased for the two-phase evaporating spray jets as compared to single-phase jets. Effect of spray evaporation on the spray jet expansion rates is also evaluated by comparing the jet expansion of the single-phase jets and those of two-phase evaporating spray jets.