Fluorescence Depolarization Investigation of the Lobed Jet 90° Twists and Structural Features

Abstract

Although lobed jets have been known for over 60 years, the causes behind their lobes generation and 90° twist has not yet been elucidated. Four vertical ethylene glycol jets were generated by 300 or 500 μm thick slit nozzles. The jets showed six lobes twisted 90° one from another. The odd and the even lobes were in the frontal and lateral planes, respectively. For each jet, the length of the lobes increased with volumetric rate while their number remained constant. Polarization maps of molecular alignment for frontal and lateral views were acquired by fluorescence depolarization (0.01 mm2 resolution). Upon their integration, velocity maps were obtained. These allowed to identify at the top of each lobe two lateral divergent inner streams that converge at the bottom. Then they merged, generating the next lobe at exactly 90°. This pattern repeated itself producing the consecutive lobes. Additionally, the polarization maps showed that lobed jets may be suitable to control molecular alignment reactions as they provide quite defined regions of high or low molecular alignment (within each lobe) and have efficient molecular mixing at the merging points (between the lobes).