Numerical modeling of high temperature shell and tube heat exchanger and chemical decomposer for hydrogen production

This thesis deals with the development of a three-dimensional numerical model of high temperature shell and tube heat exchanger and chemical decomposer to examine the percentage decomposition of a sulfur trioxide gaseous mixture for the production of hydrogen by the sulfur-iodine thermochemical water splitting cycle, a candidate cycle in the U.S. Department of Energy Nuclear Hydrogen Initiative. A counter flow type straight tube shell and heat exchanger concept is chosen for the analysis. The reacting fluid is a mixture of sulfur trioxide gas and water vapor inside the tubes of the heat exchanger and high temperature helium is the gas which flows through the shell. Proceeding with the simple, basic two-dimensional tube model, the percentage decomposition of sulfur trioxide gaseous mixture was investigated. A steady-state, laminar, two-dimensional axisymmetric shell and tube model with counter flow and parallel flow arrangements and simple uniform cubical packing was developed using a porous medium approach to investigate the fluid flow, heat transfer and chemical reactions in the decomposer. The effects of inlet velocity, temperature and the porous medium properties on the pressure drop across the porous medium were studied. The influence of geometric parameters mainly the diameter of the tube, diameter of the shell and the length of the porous zone on percentage decomposition of sulfur trioxide in the tube was investigated as well. From the performed calculations, it was found that the Reynolds number played a significant role in affecting the sulfur trioxide decomposition. The percentage decomposition decreases with an increase in Reynolds number.;Flow rate uniformity in the heat exchanger tubes was also investigated. Simulations of the three dimensional straight tube configuration, tube configuration with baffle plate arrangement and with pebble bed region inside the tubes were performed to examine the flow distribution on tube side. It was found the flow maldistribution along the tube direction is very serious with the simple tube configuration. An improvement of the header configuration has been done by introducing a baffle plate into the header section. With the introduction of the baffle plate, there was a noticeable decrease in the flow maldistribution in the tubes. Uniformity of flow was also investigated with catalytic bed inside the tubes. A significant decrease in flow maldistribution was observed with this arrangement. Simulations were performed on three dimensional numerical model of the shell and tube heat exchanger with and without baffles to evaluate the percentage decomposition of sulfur trioxide where it was found that the baffles play an important role in increasing the percentage decomposition of sulfur trioxide.