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Full-Text Articles in Engineering
Determination Of Surface Heating Distribution To Establish Targeted Thermal Tnvironments In Industry Hydrothermal Autoclaves, Hongmin Li, Guo-Xiang Wang, Edward Evans
Determination Of Surface Heating Distribution To Establish Targeted Thermal Tnvironments In Industry Hydrothermal Autoclaves, Hongmin Li, Guo-Xiang Wang, Edward Evans
Dr. Guo-Xiang Wang
This article presents a method for the determination of the heat flux distributions to establish the desired growth environments in autoclave reactors. The algorithm consists of three submodels including the inverse natural convection of the fluid, the inverse heat conduction in the metal wall, and the heat conduction in the insulation layer. The technique is employed to obtain the heat flux distributions that establish the same growth environment as the one predicted by the two-dimensional isothermal wall model. Based on the results, practical heater designs are proposed to improve the growth environments in such industry growth vessels.
Flow Of Solution In Hydrothermal Autoclaves With Various Aspect Ratios, Hongmin Li, Edward Evans, Guo-Xiang Wang
Flow Of Solution In Hydrothermal Autoclaves With Various Aspect Ratios, Hongmin Li, Edward Evans, Guo-Xiang Wang
Dr. Guo-Xiang Wang
A good understanding of the natural convective flow in hydrothermal autoclaves is essential for the control of the growth rate and the quality of the grown crystals. This paper presents a numerical simulation of turbulent natural convection in industry-size autoclaves with various aspect ratios. A simplified 2D axisymmetric model was developed. Numerical results were obtained for autoclaves with aspect ratios ranging from 2 to 20. Results show typical two counter-flow cells in both the bottom and upper chambers. Heat conduction through the baffle is negligible. Detailed analyses and discussions are presented to characterize the bulk flows in the upper chamber …
Single-And Multi-Hole Baffles-A Heat Transfer And Fluid Flow Control For Hydrothermal Growth, Edward Evans, Hongmin Li, Guo-Xiang Wang
Single-And Multi-Hole Baffles-A Heat Transfer And Fluid Flow Control For Hydrothermal Growth, Edward Evans, Hongmin Li, Guo-Xiang Wang
Dr. Guo-Xiang Wang
Hydrothermal solution growth is an important technique to grow high-quality single crystals. An autoclave, a closed cylindrical low-carbon steel vessel, is used to grow the large size crystals. A baffle located at the median height divides an autoclave into two chambers. Previous numerical studies indicate that the buoyancy-driven flow within an autoclave is very sensitive to the temperatures on the wall established by the heating. Baffles are required to establish the conditions for growth of high quality single crystals. This paper presents a numerical study of the effects of various baffles on the fluid flow and temperature fields in an …
Natural Convection Flow Structures And Heat Transfer In A Model Hydrothermal Growth Reactor, Hongmin Li, Minel Braun, Edward Evans, Guo-Xiang Wang, Govind Paudel, Jason Miller
Natural Convection Flow Structures And Heat Transfer In A Model Hydrothermal Growth Reactor, Hongmin Li, Minel Braun, Edward Evans, Guo-Xiang Wang, Govind Paudel, Jason Miller
Dr. Guo-Xiang Wang
Due to the experimental difficulties brought about by high pressure and temperature growth conditions, flow and heat transfer in industrial hydrothermal autoclaves for the growth of single quartz crystals have been studied mostly numerically. To date, most of the numerical models and associated results are not experimentally validated; only qualitative validation data from experiments done during actual crystal growth production is partly available. In this study, the authors used a model simulated reactor represented by an enclosure with two lower half sidewalls uniformly heated while the upper half sidewalls are uniformly cooled. Flow structures in the reactor are qualitatively visualized …
A Three-Dimensional Conjugate Model With Realistic Boundary Conditions For Flow And Heat Transfer In An Industry Scale Hydrothermal Autoclave, Hongmin Li, Edward Evans, Guo-Xiang Wang
A Three-Dimensional Conjugate Model With Realistic Boundary Conditions For Flow And Heat Transfer In An Industry Scale Hydrothermal Autoclave, Hongmin Li, Edward Evans, Guo-Xiang Wang
Dr. Guo-Xiang Wang
This paper presents a conjugate heat transfer model for industry size hydrothermal autoclaves. The electric heating on the wall outside surfaces is represented by constant heat fluxes. The circumferential heat flux deviation is introduced for the asymmetric factors from the surroundings. The results indicate that the temperature at the solution/wall interface is far from uniform. Circumferential temperature deviation is large enough to establish an asymmetric flow. To accurately simulate flows in industry autoclaves, one needs to use the conjugate model. The growth environment in current industry autoclaves, however, can be improved by establishing a uniform temperature on the wall/solution interface.
Three-Dimensional Flow Of Solution In An Industry-Size Hydrothermal Autoclave Subjected To Non-Uniform Heating Effects Of A Baffle On Flow And Temperature Separation, Hongmin Li, Guo-Xiang Wang, Edward Evans
Three-Dimensional Flow Of Solution In An Industry-Size Hydrothermal Autoclave Subjected To Non-Uniform Heating Effects Of A Baffle On Flow And Temperature Separation, Hongmin Li, Guo-Xiang Wang, Edward Evans
Dr. Guo-Xiang Wang
Hydrothermal growth takes place in a closed cylindrical container called an autoclave. Natural convection flow of an aqueous solution at a high temperature and a high pressure carries the nutrient. The high temperature growth condition and the natural convection flow are maintained by two independently controlled electrical heaters on the outside of the autoclave. In practice, the heating is circumferentially non-uniform. Many theoretical and numerical studies, however, assume axially symmetric heating conditions. This paper presents a numerical analysis of the three-dimensional heat transfer and fluid flow with a non-uniform heating condition. The analysis is based on an industry-size autoclave with …