The convection in melt crystal growth influences the crystal integrity deeply.During space crystal growth,the buoyancy driven convection has been eliminated for the microgravity environment,therefroe,surface tension d...The convection in melt crystal growth influences the crystal integrity deeply.During space crystal growth,the buoyancy driven convection has been eliminated for the microgravity environment,therefroe,surface tension driven convection (Marangoni Convection) become the main convection form.But the Marangoni convection forms,starting condition,development process and its influence on crystal growth are still unclear now.At the present time,Many studies focused on simulating liquid Marangoni convection or numerical simulation.However,few studies concerned on real melt,especially on oxide melt. In this paper,an in situ observation is carried out to study the start and development of Marangoni convection of Bi 12 SiO 20 melt in a 2mm diameter loop like platinum crucible.The different states of steady convection and the transition from steady to oscillatory convection are observed.The critical Marangoni number is obtained as 22433 and it agreed with a dependence Ma c=2884Pr 0.638 for high Prandtl number melt.The authors also obtained a dependence of convection oscillatory frequency on melt temperature.It increases with temperature rising.展开更多
We have investigated experimentally and theoretically the thermocapillary convective flow phenomena in a loop-shaped Pt wire heater of KNbO_(3)(20wt.%)and Li_(2)B_(4)O_(7) solution.Optical evaluations in connection wi...We have investigated experimentally and theoretically the thermocapillary convective flow phenomena in a loop-shaped Pt wire heater of KNbO_(3)(20wt.%)and Li_(2)B_(4)O_(7) solution.Optical evaluations in connection with thermocouple measurements made it possible to get a new type of thermocapillary convective flow in the considered system.To study the kinematical behavior of thermocapillary convection,we have measured the stream velocities of flow.In a theoretical analysis,the flow velocity due to thermocapillary effect alone was estimated by balancing the surface tension forces by viscous forces.The velocity distribution in the solution near the margin of the heater was obtained,which is in agreement with the experimental result.展开更多
文摘The convection in melt crystal growth influences the crystal integrity deeply.During space crystal growth,the buoyancy driven convection has been eliminated for the microgravity environment,therefroe,surface tension driven convection (Marangoni Convection) become the main convection form.But the Marangoni convection forms,starting condition,development process and its influence on crystal growth are still unclear now.At the present time,Many studies focused on simulating liquid Marangoni convection or numerical simulation.However,few studies concerned on real melt,especially on oxide melt. In this paper,an in situ observation is carried out to study the start and development of Marangoni convection of Bi 12 SiO 20 melt in a 2mm diameter loop like platinum crucible.The different states of steady convection and the transition from steady to oscillatory convection are observed.The critical Marangoni number is obtained as 22433 and it agreed with a dependence Ma c=2884Pr 0.638 for high Prandtl number melt.The authors also obtained a dependence of convection oscillatory frequency on melt temperature.It increases with temperature rising.
基金Supported by the Foundation for Kay Research Project of Microgravity Science of the State Science and Technology Commission of China(95-Yu-34)the National Natural Science Foundation of China under Grant No.59832080National Space Development Agency of Japan(NASDA).
文摘We have investigated experimentally and theoretically the thermocapillary convective flow phenomena in a loop-shaped Pt wire heater of KNbO_(3)(20wt.%)and Li_(2)B_(4)O_(7) solution.Optical evaluations in connection with thermocouple measurements made it possible to get a new type of thermocapillary convective flow in the considered system.To study the kinematical behavior of thermocapillary convection,we have measured the stream velocities of flow.In a theoretical analysis,the flow velocity due to thermocapillary effect alone was estimated by balancing the surface tension forces by viscous forces.The velocity distribution in the solution near the margin of the heater was obtained,which is in agreement with the experimental result.
