Degree Type

Dissertation

Date of Award

2016

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Major

Mechanical Engineering

First Advisor

Shankar Subramaniam

Abstract

Reacting gas-solid flows occur in nature and many industrial applications. Emerging carbon-neutral and sustainable energy generation technologies such as CO2 capture and biofuel production from fast pyrolysis of biomass are examples of reacting gas-solid flows in industry. Fundamental scientific understanding of reacting gas-solid flows is needed to overcome technological barriers for the successful development of these technologies. Multiphase computational fluid dynamics (CFD) simulations are increasingly being used for scale-up of reactors from laboratory to pilot to full-scale plants, and also for evaluation of different design options. Device-scale CFD simulations of reacting gas-solid flow are based on statistical descriptions that require closure models for interphase exchange of momentum, heat, and species. The predictive capability of multiphase CFD simulations depends on the accuracy of the models for the interphase exchange terms. Therefore, multiphase CFD simulations require accurate physics-based multiphase flow models of heat and mass transfer as well as chemical reaction rates. Particle-resolved direct numerical simulation (PR-DNS) is a first-principles approach to provided transformative insights into multiphase flow physics for model development. PR-DNS of reacting gas-solid flows can provide accurate quantification of gas-solid interactions.

The primary objective of this work is to develop improved closure models for CFD simulations in reacting gas-solid flows using the PR-DNS approach. A computational tool called particle-resolved uncontaminated-fluid reconcilable immersed boundary method (PUReIBM) has been developed as a part of this work to perform PR-DNS of heat and mass transfer in reacting gas-solid flows. A pseudo-spectral (PS) version of the PUReIBM simulation of flow past a fixed homogeneous particle assembly and freely evolving suspension of particles with heat transfer has provided PR-DNS data that are used to develop closure models in the Eulerian-Eulerian two-fluid average fluid temperature equation and probability density function transport equation, and validate the assumptions in multiphase flow statistical theories.

A fully finite-difference (FFD) version of PUReIBM is also developed to account for wall-bounded flow. The FFD PR-DNS is validated by a suite of test cases and used to perform a detailed comparison with experimental data by using the same setup. In order to extend unclosed models to account for wall effect, wall effect on drag and heat transfer of particle assemblies are studied using FFD PR-DNS. In order to validate the assumption of the isothermal particle in the case of flow past a fixed bed of particles, a preliminary study of the transient heat transfer from a single particle is performed by FFD PR-DNS. A better understanding of the role of heat and mass transfer in reacting gas-solid flow is gained by using FFD PR-DNS to simulate mass transfer in flow past a sphere with a first-order chemical reaction on the particle surface for low and high Reynolds number. These capabilities of the PR-DNS approach provide insight into flow physics and have provided data that has been used to develop improved heat transfer models for gas-solid flow.

Copyright Owner

Bo Sun

Language

en

File Format

application/pdf

File Size

357 pages

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