| Recently,with the rapid growth in the number of world economy and population,energy shortage and environmental pollution problems have become increasingly serious.The development of clean energy has become an important measure to protect the ecological environment and maintain sustainable economic development.The solar cell is supported by the country with its clean,safe and high efficiency.With its low materials loss,high growth rate and simple preparation process,ribbon silicon growth technology(horizontal ribbon growth,etc.)has been attracted a widespread attention.The preparation process of horizontal ribbon growth is the coupling process of horizontal solidification and horizontal flow.To grow higher-quality,near-single-crystalline and accurate thickness silicon wafers in a more stable growth environment,for HRG technology,it is necessary to make a deep study on researching the properties of horizontal flow and solidification of molten silicon under thermal-capillary effect.Firstly,the basic method of numerical simulation、heat transfer and flow field calculation theory of solidification process、numerical simulation of thermal-capillary convection have been studied which provided a theoretical basis for following numerical simulation.Secondly,the physical and mathematical model of horizontal flow of molten silicon under the effect of thermal-capillary are developed.The horizontal flow simulation of molten silicon under the horizontal temperature gradient Ma,the heat flux Q at the bottom of the liquid pool and two coupling effects are considered.The distribution of flow field and temperature field in liquid layer is obtained.The results found,when the heat flux Q at the bottom of the liquid pool is zero,and the temperature difference Ma between the two sides is small,the melt flow is steady.With both sides of the temperature difference Ma increases,the fluid flow is gradually transformed into steady fluctuation,once again changed with different size asymmetric twin flow two rotating in the opposite direction,finally flow transition to a state of disorder;When the temperature difference between the two sides Ma is small,the bottom heat flux Q has obvious effect on the horizontal flow of molten silicon.The fluid is changed from a steady state to a vortex cell opposite to a plurality of rotating directions.The flow configuration does not change with the increase of heat flux Q;When coupling the effect of horizontal temperature difference Ma and the vertical heat flux Q,the flow configuration is only close to the vertical heat flux Q,and the smaller heat flux has an inhibitory effect on thermal-capillary convection.Lastly,a solidification model in horizontal tube was developed by using COMSOL Multiphysics software.The adaptive mesh refinement method was adapted and the solidification process of molten silicon in horizontal tube under the coupling effect of temperature field and flow field was simulated.Apparent heat capacity method was used for solving the highly nonlinear equation.The simulation results show that the phase transition occurs in the process of horizontal solidification.Quantity of heat in the transformation process are calculated by using the mathematical analysis method of equivalent heat capacity of heat.A large amount of latent heat is released during the horizontal solidification.At the same time a distinct stratification appears in the liquid and solid phases and the specific heat of silicon alters dramatically.The morphological changes of the fused silica before and after solidification,the temperature gradient distribution before and after solidification,and the streamline velocity field distribution were observed.The result also indicates a streamline vortex flow is formed at the bottom of the crucible.It is obvious that the heat flux becomes large in the solidification and crystallization areas,and the heat flux is gradually disappeared after crystallization. |
