Abstract. A liquid jet follows a curved trajectory when the orifice from which the jet emerges is rotating. Surface tension driven instabilities cause the jet to lose coherence and break to form droplets. The sizes of the drops formed from such jets are in general not uniform, ranging from drops with diameters of the order of the jet diameter to droplets with diameters which are several orders of magnitude smaller. This presentation details a theoretical investigation of the effects of changing operating parameters on the break-up of curved liquid jets in stagnant air at room temperature and pressure. The Navier-Stokes equations are solved in this system with the usual viscous free surface boundary conditions, using an asymptotic method based upon a slender jet assumption, which is clearly appropriate from experimental observations of the jet. We also present nonlinear temporal simulations of the breakup of the liquid jets using our slender theory. These simulations based upon both a steady trajectory assumption, and the more general equations which allow for an unsteady trajectory, show all the breakup modes viewed in experiments. Satellite droplet formation is also considered.
Two-phase flow characteristics in vertical capillary downflow were investigated in order to obtain understanding of the behaviour of three-phase monolith reactors. Experiments were conducted using air and dyed water in round and square capillary tubes of 2 mm and 3 mm diameter. The flow regimes and transitions observed were recorded using high speed videography and this data was used to produce flow maps for each tube. The gas and liquid superficial velocities used ranged from 0.001 to 10 m/s and 0.0001 to 1 m/s respectively. The flow regimes and their transitions were found to be a strong function of tube geometry and surface tension effects, and some differences were observed between capillaries of round and square section. This has significant implications for the design of microchannel reactors. Annular, slug-annular, slug, bubbly and churn flow regimes were observed in the round tubes; channelling/irregular flow was observed in the square tubes in place of annular and slug-annular flow.
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