Search

The mixed convection in a fluid-porous composite medium lying inside a square cavity with a centrally rotating cylinder has been investigated in the present work. The bottom half of the cavity is filled with a porous material and the top half is filled with a clear fluid. The bottom wall of the cavity is at a higher temperature, and the top wall is at a lower temperature. The vertical walls are thermally insulated. The convection inside the cavity sets through the combined mechanisms of the thermal buoyancy force and the shearing action of the centrally rotating cylinder. The relative importance of each driving mechanism over the other is featured through the Richardson number. The Darcy-Brinkman- Forchheimer equation is used for the flow modeling in the porous medium, and a single-domain approach is adopted for the numerical solution in the fluid-porous composite medium. The simulation is carried out with ANSYS Fluent software, and a parametric analysis involving the Rayleigh number (Ra), Richardson number (Ri), and theDarcy number (Da) is conducted showing their effects on the flow and heat transfer. The phenomena are quite interesting at higher Darcy number and Rayleigh number. The distributions of isotherms, streamlines, and vector plots are plotted, along with the local Nusselt numbers for different parameters, to explore the underlying physics of the phenomenon. The system is found stable at lower Darcy number, and the heat transfer is minimum around Ri = 10. From the numerical study, an empirical correlation for the average Nusselt number is developed as a function of the other dimensionless numbers. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the flow features and device‐associated blood trauma in 4 clinical ventricular assist devices (VADs; 2 implantable axial VADs, 1 implantable centrifugal VAD, and 1 extracorporeal VAD) were computationally analyzed under clinically relevant pulsatile flow conditions. The 4 VADs were operated at fixed pump speed at a mean rate of 4.5 L/min. Mean pressure difference, wall shear stress, volume distribution of scalar shear stress (SSS), and shear‐induced hemolysis index (HI) were derived from the flow field of each VAD and were compared. The computationally predicted mean pressure difference across the 3 implantable VADs was ~70 mmHg, and the extracorporeal VAD was ~345 mmHg, which matched well with their reported pressure‐flow curves. The axial VADs had higher mean wall shear stress and SSS compared with the centrifugal VADs. However, the residence time of the centrifugal VADs was much longer compared with the axial VADs because of the large volume of the centrifugal VADs. The highest SSS was observed in one axial VAD, and the longest exposure time was observed in 1 centrifugal VAD. These 2 VADs generated the highest HI. The shear‐induced HI varied as a function of flow rate within each cardiac cycle. At fixed pump speed, the HI was greatest at low flow rate due to longer exposure time to shear stress compared with at high flow rate. Subsequently, we hypothesize that to reduce the risk of blood trauma during VAD support, shear stress magnitude and exposure time need to be minimized. [ABSTRACT FROM AUTHOR]

The present study addresses the interaction effect of participating media radiation with the onset of double-diffusive convection in a square enclosure. Vertical walls are imposed with constant temperature and concentration, and the horizontal walls are impermeable and adiabatic. The boundaries of the enclosure are diffuse-gray, and the enclosed fluid isotropically scatters, emits, and absorbs thermal radiation. Numerical simulations have been performed for both aiding and opposing buoyancy conditions. The buoyancy ratio has been varied to simulate the effect of buoyancy driven flow and compositionally driven flow, along with transition of flow between the above. Optical properties like opacity of medium, scattering albedo, Planck number, and wall emissivity have been varied to depict their influence on flow and heat transfer. The modified MAC method is used for the solution of convective transport equations. Gradient dependent consistent hybrid upwind scheme of second order ( GDCHUSSO) is used for the discretization of the convective terms. The discrete ordinate method, with S8 approximation, is used to solve the radiative transport equation. The parametric results are provided in graphical and tabular form. Flow lines, isotherms, and isoconcentration contour maps are provided to bring clarity in the understanding of the momentum, heat, and solute transport phenomenon. The stabilization effect of thermal radiation at critical buoyancy ratio for buoyancy opposed flow is observed. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (). DOI 10.1002/htj.21108 [ABSTRACT FROM AUTHOR]

In the present study, analysis has been performed to investigate the surface radiation effect on hydro-magnetic buoyant convection of an electrically conducting fluid in a differentially heated cavity. The fluid is enclosed within a gray chamber and imposed with a uniform magnetic field orthogonal to the vertical cross-sectional plane of the chamber. Numerical solution is done by control volume integration. A modified Marker and Cell method is used for the solution of the governing equation for flow transport. A gradient-dependent consistent hybrid upwind scheme of second order is used for discretization of the convective terms. The transport equation for surface radiation is solved using a net radiation method. Cross-string method is used to compute the view factor. Comprehensive studies on the controlling parameters that affect the flow and heat transfer characteristics are delineated. The results are presented in tabular and graphical form. The heat transfer and flow characteristics are depicted in form of isotherms and streamlines revealing the concealed physics of a complex phenomenon. [ABSTRACT FROM AUTHOR]

In the present study analysis has been performed for thermosolutal convection in a fluid-porous composite medium, consisting of a fluid-saturated porous medium followed by an overlaying clean medium. The fluid-porous composite medium is subjected to both a horizontal solutal and a thermal gradient. Top and bottom walls of the fluid-porous composite medium are assumed to be impermeable and adiabatic. The Darcy-Brinkman-Forchheimer model is used to study the flow through the fluid-porous composite medium. A single domain approach is taken into consideration for numerical simulation. The solution is done by control volume integration. A comprehensive analysis has been performed for various pertinent parameters to delineate their behavior. Results of the transport phenomenon have been provided in graphical and tabular form, for the complete understanding of the complex phenomenon. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21048 [ABSTRACT FROM AUTHOR]