The stability of two immiscible fluids with different densities and viscosities is examined for channel flow. A multi-domain Chebyshev collocation spectral method is used for solving the coupled Orr-Sommerfeld stability equations for the entire spectrum of eigenvalues and associated eigenfunctions. Numerical solution of the eigenvalue problem is obtained with the QZ eigenvalue solver and is validated with analytical results derived in the long and short wave limits. A parametric study is carried out to investigate the spectral characteristics and eigenfunction structures related to the shear and interfacial modes of instability. The interactions and mode switching between the two instability modes are investigated. Under certain conditions, the two modes are found to become unstable simultaneously. Mode coalescence can occur in either the stable or the unstable part of the spectrum. In general, the eigenfunction of the most dangerous mode is observed to vary sharply in the neighborhood of the interface and the critical points. C 2015 AIP Publishing LLC.

Two-phase flow in microgap channels offers highly potent thermal management capability and is the foundation for the emerging "embedded cooling" paradigm of electronic cooling. While heat transfer and pressure drop in such flows are intimately tied to their distinct forms of vapor-liquid aggregation, insufficient attention has been paid to characterizing the wave patterns and sub-regimes in high-quality microgap channel flow. The present visualization study focuses on two-phase flow in an adiabatic 184μm microgap channel operating at three mass fluxes of FC-72: 220, 420, and 620 kg m ⁄-s, with flow qualities ranging from approximately 40% to 90%. As predicted by a modified Taitel-Dukler flow regime map, annular flow is found to be the dominant flow regime for the present microgap configuration. Within the annular flow regime, unique 3-D wave patterns are observed at the liquid-vapor interface. The wavelength of these interfacial waves is observed to decrease with increasing flow quality and mass flux. Linear stability analysis of the liquid-vapor interface is found to yield strong agreement in predicted wavelength and wave growth rate distribution with the experimental results.

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We investigate the linear stability of inviscid plane Poiseuille flow between two parallel free surfaces. We show that there are short wave instabilities with eigenfunctions localized near the free surface and derive the asymptotics of these modes.

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Turbulent flow inside a cylindrical baffled stirred vessel is studied experimentally for different Reynolds numbers. A set of speed was selected ranging from 100 rpm to 350 rpm. These speeds gave high turbulence but without significant surface vortex formation. Vector field's maps and contours of time averaged velocities, for both radial and axial components in the impeller stream of a vessel stirred by a Rushton turbine, were determined by means of 2D PIV technique. This study reveals the importance of choosing the whole flow field of the entire vessel in order to provide comprehensive understanding of the flow pattern and mixing conditions which is essential for reliable design.

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