Showing papers by "Anthony G. Straatman published in 2005"

Carbon Foam: New Generation of Enhanced Surface Compact Recuperators for Gas Turbines

Abstract: The potential of porous carbon foam is explored in the context of compact recuperators for microturbine applications. Porous carbon foam has an open, interconnected pore structure and an extremely high solid-phase conductivity, which render the material a viable alternative in compact heat exchanger design. The material is also mechanically stable, non-corrosive and relatively inert to temperatures up to approximately 500°C, which make it particularly attractive for high-temperature non-oxydizing and moderate temperature oxidizing applications. Hydrodynamic and thermal engineering models are proposed based on recent work applied to air-water heat exchangers. The models are developed based on a unit-cube geometric model for carbon foam, a heat transfer model and well-established convective correlations that are extended to account for the effects of the carbon foam. The present calculations suggest that the use of carbon foam in a relatively simple configuration results in a significant reduction in thermal resistance accompanied by a rise in the hydrodynamic resistance. These preliminary results suggest that very compact heat transfer devices could be developed. With further investigation it is felt that the hydrodynamic resistance could be reduced while preserving the heat transfer performance resulting in very high-performance, compact heat transfer devices.Copyright © 2005 by ASME

A Computational Study of Gas-solid Flow in an Enhanced Solid Entrainment (ESE) Nozzle System

Abstract: A numerical study has been undertaken to explore the influence of geometry and flow parameters on the entrainment of solid in an ESE nozzle system immersed in a fluidized riser. A fully three-dimensional computational model of the nozzle system has been developed and all appropriate approximations and simplifications are described. A multi-phase Eulerian-Eulerian model incorporating the kinetic theory for solid particles is used. Numerical results are obtained using the commercial Computational Fluid Dynamics software FLUENT. The results indicate that solid entrainment in the ESE system is a strong function of both geometry and flow. The optimal entrainment is seen to occur when the ratio of the draft tube diameter D to separation distance I is approximately unity. At this value, the jet of injected gas is seen to spread fully into the opening of the draft tube causing the highest transport of solid particles through the tube. The entrainment is shown to increase with increasing jet velocity across the full range of flows considered. The results are consistent with similar experimental results. The results of this study should find immediate application in the design and implementation of ESE nozzle systems.

Benchmarking of a 3D, unstructured, finite volume code for incompressible Navier-Stokes equation on a cluster of distributed-memory computers

Abstract: The parallelization and performance of an implicit, unstructured, time-dependent computational fluid dynamics (CFD) code is described. Parallelization of the code is done within the PETSc framework using a single-program-multiple-data (SPMD) message passing model. The parallel code is shown to scale linearly within the limit of the available number of processors. A dynamic convergence criteria (DCC) is developed to enhance the performance of the code by linking the nonlinear convergence of the code and the solver convergence. The implementation of an appropriate choice of DCC in the code was shown good improvements with the speedups of over four times in terms of wall-clock time.