8. Januar 2026

MA: A model of a multi-zone furnace for ammonothermal crystal growth – comparative analysis and experimental validation of implementations in Ansys Fluent and CrysMAS

Dhruval Bipinbhai Bhandari –

This thesis develops a validated multi-zone furnace model for ammonothermal crystal growth and presents a comparative analysis of implementations in CrysMAS and Ansys Fluent. The following approaches will be investigated to take advantage of the complementary capabilities of the two softwares (CrysMAS does not allow different mesh parameters in separate fluid regions but is capable of solving the inverse problem of determining heater powers for reaching pre-defined temperatures at defined locations). Firstly, heater powers are determined from CrysMAS simulations at defined control-point temperatures under thermal conditions for both crystal growth (higher temperature at the bottom to favor convection) and etch back (higher temperature at the top). These heater outputs are then transferred to a 2D Ansys Fluent model which needs to be set up as part of the thesis, where region-specific mesh optimization enables a more detailed resolution of heat and mass transport. The simulation results are systematically compared with experimental data as well as the existing CrysMAS model to assess accuracy of the results as well as practicability and limitations of this approach. Secondly, the feasibility of treating the inverse problem as an optimization problem directly in Ansys via a surrogate model will be investigated. If time permits, a reduced model of autoclave and interior is set up, in order to incorporate supercritical ammonia either in a 2D or in a 3D Ansys model, exploiting a sector symmetry if reasonable.

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