Amaresh Dalal

Laminar natural convection in an inclined complicated cavity with spatially variable wall temperature

Abstract Natural convection in two-dimensional enclosure with three flat and one wavy walls is numerically investigated. One wall is having a sinusoidal temperature profile. Other three walls including the wavy wall are maintained at constant cold temperature. This problem is solved by SIMPLE algorithm with deferred QUICK scheme in curvilinear co-ordinates. The tests were carried out for different inclination angles, amplitudes and Rayleigh numbers while the Prandtl number was kept constant. The geometrical configurations considered were namely one, two and three undulations. The results obtained show that the angle of inclination affects the flow and heat transfer rate in the cavity. With increase in amplitude, the average Nusselt number on the wavy wall is appreciably high at low Rayleigh number. Increasing the number of undulations beyond two is not beneficial. The trend of local Nusselt number is wavy.

A Finite-Volume Method for Navier-Stokes Equations on Unstructured Meshes

A novel finite-volume formulation is proposed for unsteady solutions on complex geometries. A computer code based on a cell-centered finite-volume method is developed to solve both two-dimensional (2-D) and three-dimensional (3-D) Navier-Stokes equations for incompressible laminar flow on unstructured grids. A collocated (i.e., nonstaggered) arrangement of variables is used. The convective terms have provision for a variable upwinding factor, and the diffusion fluxes are computed in a novel and natural way. The pressure–velocity decoupling is avoided by momentum interpolation. The method is shown to have nearly second-order accuracy even on nonorthogonal grids. Some Navier-Stokes solutions, both 2-D and 3-D, are presented to verify the method with standard benchmark solutions. The comparison of present results with those in the literature is good. A computational study of 2-D laminar flow and heat transfer past a triangular cylinder in free stream is presented for the range 10 ≤ Re ≤ 200.

Numerical Study of Laminar Forced Convection Fluid Flow and Heat Transfer From a Triangular Cylinder Placed in a Channel

Computational study of two-dimensional laminar flow and heat transfer past a triangular cylinder placed in a horizontal channel is presented for the range 80≤Re≤200 and blockage ratio 1/12≤β≤1/3. A second-order accurate finite volume code with nonstaggered arrangement of variables is developed employing momentum interpolation for the pressure-velocity coupling. Global mode of cross-stream velocity oscillations predict the first bifurcation point increases linearly with blockage ratio with no second bifurcation found in the range of Re studied. The Strouhal number and rms of lift coefficient increase significantly with blockage ratio and Reynolds number while overall Nusselt number remains almost unchanged for different blockage ratios. At lower blockage ratios, flow is found to be similar to the unconfined flow and is more prone to wake instability. Instantaneous streak lines provide an excellent means of visualizing the von Karman vortex street.

Natural convection in a cavity with a wavy wall heated from below and uniformly cooled from the top and both sides

In this paper, natural convection inside a two-dimensional cavity with a wavy right vertical wall has been carried out. The bottom wall is heated by a spatially varying temperature and other three walls are kept at constant lower temperature. The integral forms of the governing equations are solved numerically using finite-volume method in the non-orthogonal body-fitted coordinate system. The semi-implicit method for pressure linked equation algorithm with higher-order upwinding scheme are used. The streamlines and isothermal lines are presented for three different undulations (1, 2 and 3) with different Rayleigh number and a fluid having Prandtl number 0.71. Results are presented in the form of local and average Nusselt number distribution for a selected range of Rayleigh number (10 0 -10 6 ).

Analysis of Entropy Generation During Mixed Convective Heat Transfer of Nanofluids Past a Square Cylinder in Vertically Upward Flow

The present work demonstrates entropy generation due to laminar mixed convection of water-based nanofluid past a square cylinder in vertically upward flow. Streamline upwind Petrov–Galerkin (SUPG) based finite element method is used for numerical simulation. Nanosized copper (Cu) and alumina (Al2O3) particles suspended in water are used with Prandtl number (Pr)1⁄4 6.2. The range of nanoparticle volume fractions considered is 0–20%. Computations are carried out at a representative Reynolds number (Re) of 100 with Richardson number (Ri) range 0.5<Ri< 0.5, both values inclusive. For both the nanofluids (Al2O3–water and Cu–water nanofluids), total entropy generation decreases with increasing nanoparticle volume fractions. It is found that for the present case of mixed convection flows with nanofluids, thermal irreversibility is much higher than that of frictional irreversibility. The Bejan number decreases with increasing nanoparticle volume fractions. [DOI: 10.1115/1.4007411]

Natural Convection in a Rectangular Cavity Heated from Below and Uniformly Cooled from the Top and Both Sides

ABSTRACT In this article, a study of natural convection inside a rectangular cavity is carried out. The bottom wall is heated by a spatially varying temperature and other three walls are kept constant at lower temperature. The integral forms of the governing equations are solved numerically using the finite-volume method in a nonorthogonal body-fitted coordinate system. The SIMPLE algorithm with higher-order upwinding scheme is used. Results are presented in the form of local and average Nusselt number distribution for a range of Rayleigh numbers (100–106) and aspect ratios (0.5, 0.75, 1, 1.25, 1.5, and 2). The streamlines and isothermal lines are presented for various Rayleigh numbers and a fluid having Prandtl number 0.71.

A Numerical Study of Fluid Flow and Heat Transfer around a Square Cylinder at Incidence using Unstructured Grids

A numerical investigation of flow and heat transfer around a square cylinder at incidence (α = 0° − 45°) is presented for a range of Reynolds numbers ( Re = 60 − 150). A finite-volume code suitable for unstructured grids has been developed to simulate the flow. The unstructured grid has been generated using the Delaunay triangulation algorithm. A modified pressure-velocity correction scheme with semi-explicit time-stepping is implemented to solve the Navier-Stokes equations. Collocated grid arrangement has been used for the dependent variables. Convective terms have been discretized using a second order upwind least squares scheme. The formation of Karman vortex street has been captured and the Strouhal number associated with the wake has been determined. The dependence of Strouhal number, force coefficients (drag and lift), moment coefficient and average Nusselt number on Reynolds number, and angle of incidence for a fixed blockage ratio has been reported and analyzed.

Analysis of Entropy Generation During Mixed Convective Heat Transfer of Nanofluids Past a Rotating Circular Cylinder

The entropy generation due to mixed convective heat transfer of nanofluids past a rotating circular cylinder placed in a uniform cross stream is investigated via streamline upwind Petrov-Galerkin based finite element method. Nanosized copper (Cu) particles suspended in water are used with Prandtl number (Pr)=6.9. The computations are carried out at a representative Reynolds number (Re) of 100. The dimensionless cylinder rotation rate, a, is varied between 0 and 2. The range of nanoparticle volume fractions (phi) considered is 0 <= phi <= 5%. Effect of aiding buoyancy is brought about by considering two fixed values of the Richardson number (Ri) as 0.5 and 1.0. A new model for predicting the effective viscosity and thermal conductivity of dilute suspensions of nanoscale colloidal particles is presented. The model addresses the details of the agglomeration-deagglomeration in tune with the pertinent variations in the effective particulate dimensions, volume fractions, as well as the aggregate structure of the particulate system. The total entropy generation is found to decrease sharply with cylinder rotation rates and nanoparticle volume fractions. Increase in nanoparticle agglomeration shows decrease in heat transfer irreversibility. The Bejan number falls sharply with increase in alpha and phi.

Effect of Undulations on the Natural Convection Heat Transfer and Entropy Generation Inside a Porous Right-Angled Triangular Enclosure

In the present study, natural convection in a two-dimensional porous right-angled triangular enclosure with one wavy wall is studied numerically. Three cases with one, two, and three undulations on the left wall are studied in this analysis. The stream function-vorticity equations are solved using finite-difference technique and a structured nonorthogonal body-fitted mesh is used for computations. The effect of Rayleigh number (Ra = 103–106), Darcy number (Da = 10−4–10−2) and undulations on the heat transfer, fluid flow, and entropy generation is investigated. It is found that average Nusselt number increases with Darcy number and number of undulations present on the left wall at fixed Darcy number.

Effect of superheat and electric field on saturated film boiling

The objective of this investigation is to study the influence of superheat temperature and applied uniform electric field across the liquid-vapor interface during film boiling using a coupled level set and volume of fluid algorithm. The hydrodynamics of bubble growth, detachment, and its morphological variation with electrohydrodynamic forces are studied considering the medium to be incompressible, viscous, and perfectly dielectric at near critical pressure. The transition in interfacial instability behavior occurs with increase in superheat, the bubble release being periodic both in space and time. Discrete bubble growth occurs at a smaller superheat whereas vapor columns form at the higher superheat values. Destabilization of interfacial motion due to applied electric field results in decrease in bubble separation distance and increase in bubble release rate culminating in enhanced heat transfer rate. A comparison of maximum bubble height owing to application of different intensities of electric field is performed at a smaller superheat. The change in dynamics of bubble growth due to increasing superheat at a high intensity of electric field is studied. The effect of increasing intensity of electric field on the heat transfer rate at different superheats is determined. The boiling characteristic is found to be influenced significantly only above a minimum critical intensity of the electric field.