Heat Transfer Performance Study Of The New-type Heat Pipes In A Polysilicon CVD Reactor

With the rapid development of electronic information techniq ue and semiconductor industry,there is an increasing demand for super high purity polysilicon in market.However,most of the polysilicon produced by traditiona l Simens process is solar grade and only a small amount of silicon can achieve the electronic grade so that it's hard to make mass production of electronic-grade polysilicon by this way.As the second popular process,the monosilane method can not only guarantee high purity of silicon but also reduce the energy consumption greatly because its decomposition temperature is in range of 650~800?.It will become more attractive in the future with the lower cost of SiH4 and the better safety condition.So it's meaningful to develop a new-type MS-Simens reactor.This paper devised the newly added heat pipe in the MS-Simens CVD reactor.The medium temperature heat pipe work between 200~350?,containing mercury as working fluid,which can transfer high quantities of heat.Stainless steel 316 L was chosen as the tube material.The diameter of the tube was designed in consideration of working limits of the heat pipe.The special structure design was accomplished based on the relative position of heat pipes and silicon rods.The strength was checked by linearization of stresses method using finite element analysis software.The heat transfer mechanism and thermal resistance model of single thermosyphon was presented.Based on the traditional N usselt theory,taking the shear force in gas-liquid interface into account,a new numerical model was proposed by establishing equilibrium equations.The results showed that the liquid is thicker than Nusselt theoretical value and the heat transfer coefficient is lower than theoretical value when calculating with water as working liquid.However the model result and theoretical value are almost the same,up to 105W/(m2?K),when calculating with mercury as working liquid.CFD simulation of cooling section of the MS-Simens reactor was calculated based on the previous results of the heating section.The results show that the velocity of fluid in the tank is rather average except near the inlet and outlet regions.The velocity near the wall is a little larger than central area where nonuniform vortexes can be found.Two length ratios(3,1.8)is compared and the result show that smaller length ratio has better turbulent motion and greater wall heat transfer coefficient.The analysis between two inlet positions shows that it's reasonable to avoid cooling water flowing over the heat pipe near the inlet.The comparison of different inlet velocities shows that the wall heat transfer coefficient and pressure drop both increase with the increase of inlet velocity.The total residence of heat pipe only drops 13.9% while inlet velocity varies from 0.5m/s to 1.5m/s so low inlet velocity is recommended.