A Chinese team led by researchers from Kunming University of Science and Technology and Yunnan Yuntong Zinc Co. built a model to simulate electric heat processing of U-shaped silicon rods in a novel four-ring, 80-rod industrial Siemens reactor.
Noting that earlier studies demonstrated that using high-frequency alternating current (AC) could “significantly improve temperature uniformity in polysilicon rods due to the skin effect,” albeit in much smaller-sized reactors, the research team developed a new heating model. It included thermal and electrical behavior and multi-ring interaction for large-scale polysilicon reduction furnaces.
In the study, “The temperature uniformity within U-style silicon located in a novel 80-rod siemens reactor with a high silicon core,” published in Results in Engineering, the team described its investigation of the effects of direct current (DC) and AC heating on thermal and electrical performance within the polysilicon reduction furnace.
The goal was to support a more uniform temperature distribution between the center and surface of the silicon rods to improve process energy efficiency.
The numerical simulations of the polycrystalline silicon material were done with Comsol software. The study also used the Joule heating model, direct current model, and heat transfer model. Details were also provided about the boundary conditions, key parameters, and how temperature gradients in the reactor were determined.
To validate the accuracy of the simulation, the voltage obtained from the model was compared to data from an industrial 80-rod polysilicon reduction reactor.
The analysis indicated that the model “accurately” predicts the thermal and electric behavior with a relative error of less than 10%, according to the paper.
The researchers said that AC heating “significantly improves temperature uniformity” and that modifying the frequency can reduce the center temperature. The regression equation based on the average data of four rings developed by the team reportedly accurately predicts with an average relative error of only 4.62%.
The team also noted the “strong” interaction between frequency and diameter at between 5 kHz and 200 kHz. Above 300 kHz, the temperature difference stabilizes, and the interaction effect weakens, it said.
The research team had members from Yunnan Yuntong Zinc Co., Kunming University of Science and Technology, Yunnan Tongwei High Purity Crystal Silicon, a unit of Tongwei, and Kunming Metallurgical Research Institute.
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