Optimization and Evaluation of Carbon/Carbon Thermal Insulation Tube CVI Densification for Czochralski Monocrystalline Silicon Rod

Crystalline silicon photovoltaic power generation is a renewable energy source vigorously developed worldwide, while high-quality carbon/carbon thermal insulation tubes serve as key core components for fabricating high-performance large-diameter photovoltaic monocrystalline silicon rods. However, the isothermal chemical vapor infiltration densification process of large-diameter carbon/carbon thermal insulation tubes is complex and difficult to predict, and how to improve the radial and axial density uniformity of the insulation tubes remains an urgent issue to be addressed. To tackle this problem, this paper constructs a transient three-dimensional multi-field coupled model for the isothermal chemical vapor infiltration densification process. An optimization strategy involving the introduction of graphite pads is proposed, and the crucial factors affecting densification, uniformity, and densification rate are investigated. Moreover, a detailed geometric model, appropriate meshing method, and effective multi-field coupled simulation scheme are developed. This establishes a highly efficient simulation framework for multi-field coupling. Additionally, the role of the graphite pad is thoroughly explored, revealing that the thickness of the graphite pad is a crucial factor influencing the densification results. Numerical results demonstrate that when the graphite pad thickness is 80 mm, the average density of the insulation tube increases by 47% (from 0.975 × 103 kg/m3 to 1.436 × 103 kg/m3), with a densification rate of 2.55 × 10−3 kg/m/s, achieving optimal performance. This work provides valuable insights for evaluating the performance of carbon/carbon thermal insulation tubes of various sizes and offers a practical process reference value for the new product development.