Numerical Modeling of Thermal and Flow Field in Directional Solidification Silicon under Vertical Magnetic Field
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ORIGINAL PAPER
Numerical Modeling of Thermal and Flow Field in Directional Solidification Silicon under Vertical Magnetic Field Wenjia Su 1
&
Wei Yang 1 & Jiulong Li 1 & Chen Li 1 & Junfeng Wang 1
Received: 14 July 2020 / Accepted: 16 November 2020 # Springer Nature B.V. 2020
Abstract One of the key issues in the directional solidification (DS) process of multi-crystalline silicon (mc-Si) is to control the melt flow in order to achieve a higher quality of silicon ingot. A steady global model is developed to investigate the effects of vertical magnetic field (VMF) variation in industrial G5 DS furnace. The Solid/Liquid (S/L) interface, thermal and flow field during directional solidification of mc-Si have been simulated. The results show that, with B0 increases, the deflection of S/L interface decreases and melt flow rate is greatly inhibited. Through the analysis of the flow structure, it is found that two small vortexes in melt without B0 become a large vortex as B0 increases. The melt flow distribution is more uniform which is beneficial to obtain a homogeneous distribution of impurities. These results show the VMF can be adjusted to successfully obtain a more uniform flow distribution and a flatter S/L interface shape. Keywords Vertical magnetic field . Directional solidification . Silicon solar cells . Solid/liquid interface . Thermal and flow field
1 Introduction Directional solidification (DS) is the most widely used method for producing multi-crystalline silicon (mc-Si) for solar cells due to its cost effectiveness [1]. It was already shown that in DS process melt convection plays an important role in the S/L interface shape and impurities distribution. Melt flow is mainly driven by three forces: thermal buoyancy, Marangoni tension and argon shear stress. Among them, the thermal buoyancy due to radial temperature gradient is the main force driving the melt flow [2–4]. The favorable melt flow structure is obtained with the assistance of external forces rather than by adjusting the thermal zone structure. Recently, magnetic field, as an effective force to control melt convection, is regarded as one of the research hotspots for optimizing crystal quality [5–11]. However, few scholars have studied the basic features of VMF on the thermal and flow field in DS process. Tanasie et al. [12] found that the interface deflection decrease slightly. Song et al. [13] found that melt convection velocity and total oxygen content * Wenjia Su [email protected] * Junfeng Wang [email protected] 1
School of Energy and Power, Jiangsu University, Zhenjiang, China
decrease significantly with the increase of the magnetic flux density. Therefore, it is still necessary to explore the internal principle of VMF on melt flow structure. As shown in Fig. 1, the principle diagram of vertical magnetic field in DS method is given. It can be seen that the charged particles move under the VMF mainly give rise to suppressing the melt flow in both radial and circumferential direction. The purpose of this article is to investigate the i
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