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R P Chhabra - One of the best experts on this subject based on the ideXlab platform.

  • effect of orientation on the steady laminar free convection heat transfer in power law fluids from a Heated triangular Cylinder
    Numerical Heat Transfer Part A-applications, 2014
    Co-Authors: Anurag Kumar Tiwari, R P Chhabra
    Abstract:

    In this work, the influence of orientation on the steady laminar free convection heat transfer from a Heated triangular Cylinder (flat side facing downward and upward) in quiescent power-law fluids has been investigated. In particular, the coupled momentum and energy equations have been solved numerically over wide ranges of the relevant dimensionless parameters as: Grashof number (10 ≤ Gr ≤ 105), Prandtl number (0.72 ≤ Pr ≤ 100), and power-law index (0.3 ≤ n ≤ 1.8). The detailed flow and temperature fields in the vicinity of the Heated Cylinder are visualized in terms of the streamline and isotherm contours, respectively. At the next level, the influence of each of the governing parameters, namely, Grashof number (Gr), Prandtl number (Pr), and power-law index (n) on the local and average Nusselt number and drag coefficient, is examined. The flow separation was found to occur at high Grashof numbers and low Prandtl numbers, but only in shear-thickening and Newtonian fluids (n ≥ 1) for the Cylinder orienta...

  • Free convection from a Heated circular Cylinder in Bingham plastic fluids
    International Journal of Thermal Sciences, 2014
    Co-Authors: N Nirmalkar, A. Bose, R P Chhabra
    Abstract:

    Abstract In this work, the equations of motion and energy have been solved numerically using Comsol Multiphysics (version 4.3a) for the laminar free convection heat transfer from a horizontal Heated Cylinder to Bingham plastic fluids over the range of conditions as: Rayleigh number, 102 ≤ Ra ≤ 106; Prandtl number, 30 ≤ Pr ≤ 100 and Bingham number, 0 ≤ Bn ≤ 104. Extensive results on the streamline and isotherm contours, yielded/unyielded regions, local and average Nusselt numbers are presented and discussed. Owing to the presence of the fluid yield stress, both fluid-like (yielded) and solid-like (unyielded) regions coexist in the flow domain depending upon the prevailing stress levels vis-a-vis the value of the fluid yield stress. Naturally, heat transfer in the solid-like regions occurs purely by conduction and convection is thus restricted to the fluid-like regions. Furthermore, the yielded regions progressively diminish with the increasing value of the Bingham number and/or the decreasing value of the Rayleigh number as the buoyancy-induced flow weakens. All in all, the overall rate of heat transfer is determined by the gradients on the surface of the Heated Cylinder. Finally, the present numerical values of the average Nusselt number have been correlated in terms of the modified Rayleigh number (Ra∗) and Prandtl number (Pr∗).

  • free convection from a Heated circular Cylinder in confined power law fluids
    International Journal of Thermal Sciences, 2013
    Co-Authors: Radhe Shyam, N Nirmalkar, M Sairamu, R P Chhabra
    Abstract:

    Abstract In this work, free convection heat transfer from a horizontal Cylinder (isothermal or dissipating heat at a constant rate) placed on the horizontal axis of a square duct filled with an incompressible power-law fluid has been investigated. On the other hand, along the vertical centre line, three relative positions of the Heated Cylinder are considered, namely, at the centre, close to the upper wall and close to the bottom wall to elucidate the effect of the symmetric and asymmetric confinement. The governing differential equations, namely, continuity, momentum and energy have been solved numerically to elucidate the effect of the pertinent kinematic (Rayleigh number, Ra; Prandtl number, Pr; power-law index, n ) and geometric parameters, especially the relative positioning of the Heated Cylinder with reference to the bottom wall. Overall, the present results span the wide range of conditions as 10 2  ≤ Ra ≤ 10 6 ; 0.71 ≤ Pr ≤ 100; 0.2 ≤  n  ≤ 1.8 and 0.25 ≤  β 1  ≤ 0.75, and the flow is believed to be laminar and steady over this range of Rayleigh numbers. Overall, the average Nusselt number shows positive dependence on Grashof number and Prandtl number. The overall heat transfer also decreases as the Cylinder gradually approaches the upper adiabatic wall. The streamline and isotherm contours reveal interesting flow patterns which show a rather strong dependence on the value of β 1 .

  • Laminar forced convection heat transfer from a Heated square Cylinder in a Bingham plastic fluid
    International Journal of Heat and Mass Transfer, 2012
    Co-Authors: N Nirmalkar, R P Chhabra, Robert J Poole
    Abstract:

    Abstract In this work, the momentum and heat transfer characteristics of a Heated Cylinder of square cross-section immersed in a streaming Bingham plastic medium have been studied. The governing differential equations (continuity, momentum and thermal energy) have been solved numerically over wide ranges of conditions as: plastic Reynolds number, 0.1 ⩽ Re ⩽ 40 , Prandtl number, 1 ⩽ Pr ⩽ 100 and the Bingham number, 0 ⩽ Bn ⩽ 100 . Over this range of conditions, the flow is expected to be symmetric and steady. The detailed flow and temperature fields in the vicinity of the Cylinder surface are examined in terms of streamline and isotherm profiles respectively. In particular, owing to the presence of the yield stress, the so-called yielded (fluid-like) and unyielded (solid-like) regions are delineated in the flow domain as functions of the Reynolds and Bingham numbers. This objective is accomplished by a detailed examination of the velocity profiles and shear rate profiles along the center planes. Further insights are developed in terms of the distribution of the pressure and local Nusselt number along the Cylinder surface together with their average values in terms of drag coefficients and mean Nusselt number. The present numerical results on drag and Nusselt number (in the form of j-factor) have been correlated to the modified Bingham and Reynolds numbers via simple expressions thereby enabling their interpolation for the intermediate values of these dimensionless parameters.

  • laminar forced convection heat transfer from a rotating Cylinder to power law fluids
    Numerical Heat Transfer Part A-applications, 2011
    Co-Authors: Saroj K Panda, R P Chhabra
    Abstract:

    Forced convection heat transfer from a Heated Cylinder rotating in streaming power-law fluids has been investigated in this work. The governing differential equations have been solved numerically to elucidate the influence of power law index (n = 0.2, 0.6, and 1), Prandtl number (1 ≤ Pr ≤ 100), Reynolds number (1 ≤ Re ≤ 40), and nondimensional rotational velocity (0 ≤ α ≤ 6) on the detailed temperature field, distribution of Nusselt number on the surface of the Cylinder and on the mean Nusselt number. As expected, the mean Nusselt number shows positive dependence on both Reynolds and Prandtl numbers, which is obviously due to the gradual thinning of the boundary layer. Furthermore, the mean Nusselt number also conforms to the conventional scaling of Pr1/3 . For a non-rotating Cylinder, all else being equal, shear-thinning facilitates heat transfer. This is also true for a rotating Cylinder up to Re ∼ 1 and rotational velocity α ≤ 4 for all values of Prandtl number used in this work. As the Reynolds number...

Chuanchieh Liao - One of the best experts on this subject based on the ideXlab platform.

  • influence of prandtl number on the instability of natural convection flows within a square enclosure containing an embedded Heated Cylinder at moderate rayleigh number
    Physics of Fluids, 2015
    Co-Authors: Chuanchieh Liao, Chaoan Lin
    Abstract:

    Influence of Prandtl number (0.07 ≤ Pr ≤ 7) on the buoyancy induced flow within a square domain containing an embedded Heated Cylinder is investigated numerically at moderate Rayleigh number (2 × 105 − 2 × 106). In general, reduction of Prandtl number thickens the thermal boundary layer, and hence, the decrease of predicted Nusselt number is observed. However, the dynamic boundary layer becomes thin and this leads to the increase of internal counter rotating vortex pairs and further to the breakdown of vortex symmetry and hence the eventual instability. In the unsteady regime, the Nusselt number oscillation frequency is as expected twice of other flow variables and increases with the reduction of Prandtl number. For the Rayleigh number investigated, the unsteady-regime is dominated by the growth of thermal boundary layer and hence the averaged Nusselt number decreases accordingly. Also, different scaling laws for the Nusselt number exist due to the change of vortex structures in the steady and unsteady re...

  • influence of prandtl number on the instability of natural convection flows within a square enclosure containing an embedded Heated Cylinder at moderate rayleigh number
    Physics of Fluids, 2015
    Co-Authors: Chuanchieh Liao, Chaoan Lin
    Abstract:

    Influence of Prandtl number (0.07 ≤ Pr ≤ 7) on the buoyancy induced flow within a square domain containing an embedded Heated Cylinder is investigated numerically at moderate Rayleigh number (2 × 105 − 2 × 106). In general, reduction of Prandtl number thickens the thermal boundary layer, and hence, the decrease of predicted Nusselt number is observed. However, the dynamic boundary layer becomes thin and this leads to the increase of internal counter rotating vortex pairs and further to the breakdown of vortex symmetry and hence the eventual instability. In the unsteady regime, the Nusselt number oscillation frequency is as expected twice of other flow variables and increases with the reduction of Prandtl number. For the Rayleigh number investigated, the unsteady-regime is dominated by the growth of thermal boundary layer and hence the averaged Nusselt number decreases accordingly. Also, different scaling laws for the Nusselt number exist due to the change of vortex structures in the steady and unsteady regions. Rayleigh number and Boussinesq number are the proper scaling parameters in the respective steady and unsteady regions with higher and lower Prandtl numbers.

  • simulations of natural and forced convection flows with moving embedded object using immersed boundary method
    Computer Methods in Applied Mechanics and Engineering, 2012
    Co-Authors: Chuanchieh Liao
    Abstract:

    In the present study, an immersed-boundary method is adopted to simulate natural and forced convection within a domain with complex geometry at low Reynolds numbers. The method is based on the direct momentum and energy forcing on a Cartesian grid, and issues involving the influence of the solid-body-forcing and the implementation of the isothermal and isoflux boundary conditions are addressed. It was shown that the second-order accuracy of global error norms of the method was ascertained only when the solid-body-forcing in velocity is implemented. On the other hand, the solid-body-forcing of the thermal field is not essential. Also, the solid-body-forcing in velocity has negligible influence on the thermal and dynamic field with stationary embedded object. Further test problems are simulated to examine the validity of the present technique: 2-D flows induced by natural convection in the annulus between two horizontal concentric Cylinders, moving Heated Cylinder within a stationary fluid, transversely oscillating Cylinder with different excitation frequencies, and 3-D simulation of a Heated sphere settling under gravity in a static fluid. All computed results are in general good agreement with previous experimental measurements and numerical simulations.

Chaoan Lin - One of the best experts on this subject based on the ideXlab platform.

Masuro Ogawa - One of the best experts on this subject based on the ideXlab platform.

  • thermal analysis of Heated Cylinder simulating nuclear reactor during loss of coolant accident
    Journal of Nuclear Science and Technology, 2014
    Co-Authors: Hiroyuki Sato, Hirofumi Ohashi, Yukio Tachibana, Kazuhiko Kunitomi, Masuro Ogawa
    Abstract:

    Transient analyses of temperature behavior of reactor during complete loss-of-coolant conditions throughout the entire period of accident with scram are presented. The influence of reactor thermal properties, operating power density, geometry of active core and selection of fuel type on the capability of decay heat removal against the accident are studied. It is shown that the reactor design envelope against loss-of-coolant accidents is fully determined by the key parameters: operating power density, volumetric heat capacity and thermal conductivity. The range of the envelope is shown to enlarge considerably by selecting high refractory fuel. Above 10% of operating power density in the current nuclear power plants, decay heat removal is not feasible without the presence of coolant in the reactor. The results suggest sufficient amount of solid materials, made of high-thermal conductance materials such as SiC and graphite, are required inside the reactor to achieve successful decay heat removal in loss-of-c...

  • thermal analysis of Heated Cylinder simulating nuclear reactor during loss of coolant accident
    Journal of Nuclear Science and Technology, 2014
    Co-Authors: Hiroyuki Sato, Hirofumi Ohashi, Yukio Tachibana, Kazuhiko Kunitomi, Masuro Ogawa
    Abstract:

    Transient analyses of temperature behavior of reactor during complete loss-of-coolant conditions throughout the entire period of accident with scram are presented. The influence of reactor thermal ...

Sauro Succi - One of the best experts on this subject based on the ideXlab platform.

  • immersed boundary thermal lattice boltzmann methods for non newtonian flows over a Heated Cylinder a comparative study
    Communications in Computational Physics, 2015
    Co-Authors: Amiri A Delouei, M Nazari, M H Kayhani, Sauro Succi
    Abstract:

    In this study, we compare different diffuse and sharp interface schemes of direct-forcing immersed boundary — thermal lattice Boltzmann method (IB-TLBM) for non-Newtonian flow over a Heated circular Cylinder. Both effects of the discrete lattice and the body force on the momentum and energy equations are considered, by applying the split-forcing Lattice Boltzmann equations. A new technique based on predetermined parameters of direct forcing IB-TLBM is presented for computing the Nusselt number. The study covers both steady and unsteady regimes (20

  • non newtonian unconfined flow and heat transfer over a Heated Cylinder using the direct forcing immersed boundary thermal lattice boltzmann method
    Physical Review E, 2014
    Co-Authors: Amiri A Delouei, M Nazari, M H Kayhani, Sauro Succi
    Abstract:

    In this study, the immersed boundary--thermal lattice Boltzmann method has been used to simulate non-Newtonian fluid flow over a Heated circular Cylinder. The direct-forcing algorithm has been employed to couple the off-lattice obstacles and on-lattice fluid nodes. To investigate the effect of boundary sharpness, two different diffuse interface schemes are considered to interpolate the velocity and temperature between the boundary and computational grid points. The lattice Boltzmann equation with split-forcing term is applied to consider the effects of the discrete lattice and the body force to the momentum flux, simultaneously. A method for calculating the Nusselt number based on diffuse interface schemes is developed. The rheological and thermal properties of non-Newtonian fluids are investigated under the different power-law indices and Reynolds numbers. The effect of numerical parameters on the accuracy of the proposed method has been investigated in detail. Results show that the rheological and thermal properties of non-Newtonian fluids in the presence of a Heated immersed body can be suitably captured using the immersed boundary thermal lattice Boltzmann method.