| Crystal materials have been applied extensively in daily life and industrial areas,with the development of space technology,people found that the stripes of crystal are greatly reduced in the microgravity environment with an extremely low buoyancy effect.However,in this situation,the surface tension gradient driven flow-thermocapillary flow-could affect the quality of crystal materials.Thermocapillary convection in a differentially heated rectangular cavity with a single/double layer fluid is studied,and the effects of Marangoni number(Ma),Rayleigh number(Ra),Prandtl number(Pr),aspect ratio(Ar),free surface heat transfer,wall surface properties and physical parameters of the encapsulant on the flow and heat transfer have been discussed in the microgravity and gravity environment respectively,the specific studies are as follows:Firstly,the effects of Ma,Ra,Pr,Ar and free surface heat transfer on thermocapillary convection in a single layer fluid is studied.It was found that,in the microgravity environment,the difference in the temperature field is tiny as Pr varied in a certain range with Ma fixed;the thermal diffusion plays a main role in the low region of the liquid layer with Ar large enough;the thermocapillary convection is enhanced with increased Ma and Ar,and weakened with increased Pr;the thermocapillary convection is enhanced with increased heat loss or heat gain of the free surface,and weakened with increased Bi while the free surface both has heat loss and heat gain.In the gravity environment,thermocapillary dominates the flow for Bd over the range-0.1?1;buoyancy dominates the flow for Bd<-103 or Bd>100 but thermocapillary still has a significant effect near the cold wall end and this effect has been enhanced with increased Ra;the buoyancy-thermocapillary convection is enhanced with heat loss while the buoyancy effect is weakened and the thermocapillary effect enhanced with heat gain,the buoyancy effects is enhanced and the thermocapillary effect weakened with Bi while the free surface both has heat loss and heat gain.Secondly,the effects of the height,width and spacing of the rough particles on thermocapillary convection in a single layer fluid with rectangular rough particles orderly distribute over the walls are explored.The results show that with the height of rough particles increased the flow is enhanced in the microgravity environment,but weakened in the gravity environment,the flow is nearly unaffected by the width of rough particles,and the spacing of rough particles has a significantly influence on the flow near the walls;the variation trend of heat transfer rate with the height,width and spacing of rough particles is related to Ma and independent of Ra,and the heat transfer rate with rough walls is less than that of the corresponding smooth walls.Finally,the effects of physical parameters of the encapsulant and free surface heat transfer on thermocapillary convection in a double layer fluid are studied.It was found that,in the microgravity environment,the thermocapillary convection in the melt has been suppressed by introduced an encapsulant with large Ma,density and viscosity while the flow in the melt does not change direction;the flow in the encapsulant and melt are both enhanced as the free surface heat loss,the flow in the encapsulant is enhanced and in the melt does not change significantly as the free surface heat gain,the flow in the encapsulant is weakened and in the melt enhanced with Bi while the free surface both has heat loss and heat gain.In the gravity environment,the flow in the upper region of the melt has been effectively suppressed by choosing a proper density ratio,and the flow in the melt has been better suppressed by introduced an encapsulant with larger viscosity;as the free surface heat loss the flows in the encapsulant and melt are both enhanced,as the free surface heat gain the flow in the melt is weakened,as the free surface both has heat loss and heat gain the flow in the encapsulant is enhanced and in the melt nearly unaffected with Bi. |
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