Fluid Flow and Heat Transfer in Serpentine Channels at Low Reynolds Numbers

Fluid flow and heat transfer in a two-dimensional serpentine channel was investigated numerically for Reynolds numbers between 175 and 725. A fifth-order finite differencing scheme was employed to carry out the computations. Three different geometries were studied. All three geometries consisted of the same wave length and the same shape of top and bottom walls, but different channel heights. In addition, two different inlet/outlet boundary conditions were investigated. It was found that the heat transfer as well as the pressure drop increase with decreasing channel height. For a given channel height, the results show that the time-averaged mean Nusselt number as well as the time averaged mean friction factor scale linearly with the Reynolds number.Air Conditioning and Refrigeration Project 6

Numerical Study of Flow and Heat Transfer in Wavy Passages

Flow and heat transfer in a wavy passage are analyzed using an accurate numerical scheme that solves the two-dimensional unsteady flow and energy equations, for both developing and periodically fully-developed flow conditions. Developing flow calculations are presented for two different wavy channels, each consisting of 14 waves. It is observed that the flow is steady in part of the channel and unsteady in the remainder. As the Reynolds number is progressively increased, the unsteadiness is onset at a much earlier location, leading to increased heat transfer rates. Calculations for fully-developed flow were performed using periodic boundary conditions. The ensuing results reveal the effects of individually varying the height, amplitude, and wavelength of a selected wavy passage.Air Conditioning and Refrigeration Project 6

Large Eddy Simulations of Particle Dispersion and Deposition in a Turbulent Square Duct Flow

In the current dissertation work, the preferential concentration and deposition of heavy solid particles in a downward, fully developed turbulent square duct flow are studied using large eddy simulations. A second-order accurate, finite-volume based fractional step scheme, based on an unstructured Cartesian mesh, is used to integrate the unsteady, incompressible, three-dimensional Navier-Stokes equations. An algebraic multigrid solver is used to solve the Poisson equation resulting from the fractional step method. The subgrid stresses are modeled with a dynamic subgrid kinetic energy model. The particle equation of motion includes drag, lift and gravity forces and is integrated using the fourth-order accurate Runge-Kutta method. The Reynolds number for the square duct is 360, based on average friction velocity and duct width. The grid used is 80??80??128 in the two wall-normal and streamwise directions, respectively. The preferential concentration of particles is studied assuming that the particles do not modify the turbulence and that particle-particle collisions are insignificant. The continuous and the dispersed phases are treated using Eulerian and Lagrangian approaches, respectively. Four cross-sectional locations representative of the time - mean secondary flow patterns and six particle response times were chosen to study the effect of location and particle inertia on preferential concentration. Variation of vorticity magnitude, swirling strength, strain-rate, and ??u:??u, and their probability distribution functions(PDF), with particle response time and location is shown to demonstrate preferential concentration. Particles are seen to accumulate in regions of high ??u:??u and strain-rate and in regions of low swirling strength. In general, particles accumulate in regions of low vorticity magnitude. However, near the wall, large particles accumulate in regions of high vorticity magnitude. In addition, instantaneous contours of the above statistics and scatter plots of particle positions in a near-wall plane are presented to illustrate preferential concentration. Deposition of particles in a square duct is the focus of the second set of simulations. Ten particle response times are studied. Simulations are carried out using one-way coupling as well as select cases using two- and fourway coupling. A particle -particle collision algorithm has been developed. PDFs of deposition location, average streamwise and wall-normal deposition velocities, and deposition rates are presented.Air Conditioning and Refrigeration Project 12

Fully-coupled solution of pressure-linked fluid flow equations

A robust and efficient numerical scheme has been developed for the solution of the finite-differenced pressure linked fluid flow equations. The algorithm solves the set of nonlinear simultaneous equations by a combination of Newton's method and efficient sparse matrix techniques. In tests on typical recirculating flows the method is rapidly convergent. The method does not require any under-relaxation or other convergence-enhancing techniques employed in iterative schemes. It is currently described for two-dimensional steady state flows but is extendible to three dimensions and mildly time-varying flows. The method is robust to changes in Reynolds number, grid aspect ratio, and mesh size. This paper reports the algorithm and the results of calculations performed

Mesoscale numerical prediction of fluid flow in a shear driven cavity

In this paper, a detailed analysis of the lattice Boltzmann method is presented to simulate an incompressible fluid flow problem. Thorough derivation of macroscopic hydrodynamics equations from the continuous Boltzmann equation is performed. After showing how the formulation of the mesocale particle dynamics fits into the framework of lattice Boltzmann simulations, numerical results of lid-driven flow inside square and triangular cavities are presented to highlight the applicability of the approach. The objective of the paper is to gain better understanding of this relatively new approach for applied engineering problems in fluid transport phenomena