Enhancement of Mixed Convection Heat Transfer in a Long Horizontal Channel with Multiple Rotating Cylinders
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Two-dimensional, laminar, steady mixed convection heat transfer in a long horizontal channel has been investigated numerically with flow modulation through periodically distributed heat conducting rotating cylinders. The upper wall of the channel is maintained at constant low temperature and the lower wall is maintained at constant high temperature. A series of heat conducting rotating cylinders is placed periodically along the centerline of the channel with a spacing between two successive cylinders being equal to the height of the channel. The mathematical model of the present problem is presented by two-dimensional continuity, momentum and energy equations considering thermal buoyancy and conduction within the cylinder. The governing equations which are presented in non-dimensional form are solved by using Galerkin finite element method with triangular discretization system. Water, air and liquid Gallium are considered as the working fluids. Numerical simulation is performed for case of pure mixed convection heat transfer characterized by a Richardson number of unity. Parametric simulation is carried out for a wide range of Reynolds numbers (1 ≤ Re ≤ 500) based on the dynamic condition of the rotating cylinder. Numerical results are presented and analyzed in terms of the distribution of streamline and isotherm patterns, local and average Nusselt number variation along the hot wall for different parametric conditions. It is found that, presence of heat conducting rotating cylinder increases the heat transfer significantly particularly in the lower range of Reynolds numbers considered in the present study and enhancement of heat transfer occurs as the Prandtl number increases. Thus, dynamic condition of the rotating cylinder and the thermophysical properties of working fluid play dominant roles for enhancing the heat transfer characteristics and flow behavior within the long horizontal channel.
Numerical Study of Laminar Mixed Convection in a Cu-Water Nanofluid Filled Lid Driven Square Enclosure with an Isothermally Heated Cylinder
A numerical study of two-dimensional, laminar, steady mixed convection heat transfer characteristics in a Cu-water nanofluid filled lid driven square cavity with an isothermally heated cylinder has been conducted. The wall of the cylinder is maintained at constant high temperature whereas the walls of the cavity (including the lid) are maintained at constant cold temperature. The isothermally heated cylinder is placed at the center of the cavity. The fluid flow in the cavity is driven by the temperature gradient and the top moving wall in the +x direction, while all other walls are stationary. The developed mathematical model, where thermal buoyancy is considered, is governed by the two-dimensional continuity, momentum and energy equations. The governing equations (mass, momentum and energy) which are expressed in non-dimensional form are solved by using Galerkin finite element method with triangular discretization system. The working fluid inside the cavity is Cu–water nanofluid where water has been considered as the base fluid. The influence of the Reynolds number (1 ≤ Re ≤ 500) based on the dynamic condition of the top moving wall (lid) and solid volume fraction of the Cu nanoparticle (0 ≤ Ï• ≤ 0.05) on fluid flow and heat transfer has been numerically investigated in the case of pure mixed convection heat transfer characterized by a Richardson number of unity. Obtained results are analyzed and presented in terms of the distribution of streamlines and isothermal contours, local Nusselt number as well as average Nusselt number variation on the cylinder surface for different parametric conditions. It is observed that enhancement of heat transfer occurs significantly as Reynolds number and solid volume fraction of nanoparticle increase. Thus, dynamic condition of the moving lid and solid volume fraction of the nanoparticle can be used as parameters for enhancing the heat transfer characteristics and flow behavior in the cavity.
Mixed Convection in a Differentially Heated Cavity With Local Flow Modulation via Rotating Flat Plates
Mixed convection in a cavity arising from thermal buoyancy force and through local
modulation via rotating at plate has been investigated. The model consists of a square cavity with the left and right vertical walls kept at constant high and low temperatures respectively while the top and bottom walls are adiabatic. Two clockwise rotating at plates, having negligible thickness in comparisonto their lengths, acting as ow modulators have been placed vertically along the centerline of the cavity.
The moving boundary problem due to plate motion in this study has been solved by implementing
Arbitrary Lagrangian Eulerian (ALE) finite element formulation with triangular discretization scheme.
Computations are performed for air (Pr = 0.71) at various Rayleigh numbers (1e2 < Ra < 1e6).
Rotational Reynolds number based on plate dynamic condition has been considered to be constant at
430. Numerical results identify critical Rayleigh number Ra(Critical) = 0.41 x 1e6 beyond which two smaller flow modulators are more effective than a single larger modulator. Thermal oscillating frequency was observed to be insensitive to Rayleigh number for the case of double modulators.
