In this work, subcooled droplet impact on a highly thermally conductive spherical surface was investigated both theoretically and experimentally. Specifically, the effect of Weber number on spreading of droplets of three different liquids namely water, isopropyl alcohol and acetone was studied. The droplet shape evolution and surface wetting upon droplet impact at surface temperatures ranging between 20 o C and 250 o C were investigated using a high speed camera. Maximum droplet spread was measured and compared with available correlations. Generally wetting contact was observed at surface temperatures below or close to saturation temperature whilst a non-wetting contact was exhibited at surface temperatures significantly greater than the saturation temperature. The drop in surface temperature was found to be significantly lower in this non-wetting contact regime which led to significant reduction in heat transfer coefficient. Despite a very small temperature drop in the film boiling regime indicating small fraction of vaporization, Schlieren imaging of acetone droplets showed qualitative vapour field around the rebounding droplets. The droplet spreading patterns in cold condition and film boiling regime were simulated using the 3D CFD models which were found to be in good agreement with the experimental observations.

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Two-fluid Taylor-vortex flow in coaxial cylinders with a stationary outer cylinder and a rotating inner cylinder has potential advantages over the conventional extraction equipment in chemical and bioprocess industries. The two phase flow behavior in the vertical annular region is either in the form of homogeneous dispersion, banded dispersion, segregated or the stratified flow with both the phases retaining individual integrity. Computational fluid dynamics (CFD) simulations have been carried out for the annular region. The effect of physical properties like density difference, interfacial tension, and the effect of geometrical parameters such as annular gap have been studied. The various regime transmissions have been investigated using CFD as well as flow visualization by particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF). The flow pattern has also been measured and compared with the CFD predictions. An attempt has been made to present the results on transition in the form of a regime map with the Eotvos and Taylor numbers as the two coordinates.

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Flow between two concentric cylinders with high-speed rotation of the inner cylinder, also termed as turbulent Taylor-Couette flow, is an integral part of annular centrifugal extractor (ACE). The vortex motion in the annular region causes intense mixing, of the two liquids, and their separation occurs in the inner cylinder under centrifugal action. In the present work, a systematic study of residence time distribution (RTD) in the annular region of ACE has been carried out experimentally as well as using computational fluid dynamics (CFD). The effects of rotational speed (10 e ω e 40, r/s), aspect ratio of annulus (11 e Γ e 48), width of annular gap (1.5 e d e 6.5, mm), and the flow ratio of the immiscible fluids (0.73 e FR e 2.4) have been systematically investigated. Effect of flow ratio, annular gap, and rotational speed has been investigated on the RTD. It was found that the flow in ACE is near to back-mixed behavior because of the presence of counterrotating vortices. The number of vortices depends on the rotational speed and the geometrical parameters of ACE. An attempt has been made to reduce back-mixing by providing radial baffles in the annulus. Good agreement was observed between the experimental measurements and CFD predictions of RTD.

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