Numerical Simulation and Experimental Validation of Fluid Flow and Mass Transfer in an Ammonothermal Crystal Growth Reactor

Due to their physical properties, gallium nitride crystals are in high demand in applications including light emitting diodes, high power and high frequency devices. One way of growing the crystals is the ammonothermal growth process. The process consists of chemical reactions occurring in reactors under high temperature and high pressure conditions. A basket of gallium nitride nutrient is inserted inside the reactor filled with ammonia and a mineralizer, whereupon gallium nitride is dissolved and transported by natural convection and then deposited onto the seeds. Because the etching and deposition reactions require temperatures in the range of 600 to 1,000 K (620 to 1,340 °F) and pressures in the range of 1,000 to 6,000 bar (14,504 to 87,022 psi), it is impossible to visualize the flow or measure its parameters.This dissertation presents a way to look inside an ammonothermal crystal growth reactor by simulating the process using CFD software. An equivalent reactor and crystal growth environment are created to provide experimental validation. The equivalent reactor respects geometric and dynamic similitude with respect to the actual ammonothermal crystal growth reactor. Experimental temperatures and velocities are recorded and compared with numerical results. Three turbulence models and the laminar model were tested. The laminar and the standard k-omega models performed better compared with experimental results. By simulating an equivalent reactor that allows visualization and measurements, the CFD model was validated.With the validated model, simulations of the actual growth process including mass transfer were performed. The wall temperature profile, the geometry of the nutrient basket, and the baffle were used as parameters to investigate their influence on the deposition rates. The temperatures on the outer walls of the reactor have a great influence on the deposition rate and can lead to etching of the seeds instead of crystal growing. The presence of a baffle inside the reactor also has a great influence on the deposition rates, and the need to find an optimal configurations became obvious. The geometry and the nature of the nutrient basket proved to be a great parameter to improve the deposition rates.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor dc:publisher

University of Akron

Year dc:date

2013

Author dc:creator

• Moldovan, Stefan Ilie

Contributors dc:contributor

• Braun, Minel
• Chandy, Abhilash

• Mechanical Engineering
• Ammonothermal crystal growth
• natural convection inside cylindrical enclosures
• surface reactions
• reactions in porous medium
• flow in porous medium
• turbulent natural convection flow
• unsteady laminar flow.

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=akron1366033161

OAI identifier oai:identifier

oai:etd.ohiolink.edu:akron1366033161