Award Date

1-1-2008

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Committee Member

Yitung Chen

Number of Pages

109

Abstract

This thesis deals with the development of a three-dimensional computational model of high temperature heat exchanger and decomposer for hydrogen production by the sulfur iodine thermochemical water splitting cycle. The present study is concerned with the use of a bayonet type heat exchanger that is a silicon carbide integrated decomposer (SID) which decomposes sulfuric acid to produce sulfur dioxide, oxygen and water. The Sandia National Laboratories (SNL) Integrated Decomposer is a SiC based design concept that uses a SID for boiling, superheating and decomposing functions where the temperatures are above 250°C; From the literature review it can be found that many researches on bayonet heat exchangers have been done in the past but there are no reports on the application of the bayonet heat exchanger as a decomposer for the catalytic sulfuric acid decomposition. In the present study, fluid flow, heat transfer and chemical reaction of the decomposer for the detailed two-dimensional analysis using volume-averaged porous media approach and three-dimensional analysis with different arrangements and different types of pellets in the packed bed have been studied. The computational model was validated by comparisons with experimental result obtained from SNL; The pre-processor GAMBIT was used to create a computational mesh and the CFD software package FLUENT that is based on the finite volume method is used to produce numerical results. The equations governing the flow and heat transfer are solved numerically using finite volume techniques, additional transport equations are also solved for chemical reactions; A two-dimensional axisymmetric computational model with porous medium region located in the decomposer region with uniformly packed spherical pellets was used to calculate the decomposition of sulfur trioxide. The working fluids in the model are sulfur trioxide, sulfur dioxide, oxygen and water vapor. Parametric studies for different surface-to-volume ratios, Reynolds number and operation pressures are performed; To enhance the thermal efficiency of the decomposer and to decrease swirling, a three-dimensional computational model with packed bed region containing different types and arrangements of pellets is developed. The experiment was done by varying the pressure from 3 to 4.8 bar and acid flow rate from 5--15 ml/min. The decomposition percentage obtained from SNL with SID alone is 60% and SID with concentrator is 37%. The decomposition percentage obtained from numerical results is consistent with the experimental results. From the result it was found that the sulfur dioxide production (throughput) is maximum for the packed bed region with hollow cylindrical pellets.

Keywords

Bayonet; Decomposer; Exchanger; Heat; High; Hydrogen; Numerical; Production; Study; Temperature

Controlled Subject

Mechanical engineering

File Format

pdf

File Size

3297.28 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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