Convective mixing streamlines

Figure 18.55 shows the predicted steady-state temperature and meridional flow streamlines for (a) no melt convection and stationary crystal, (b) no crystal rotation with buoyancy-induced melt flow, (c) modest rotation and mixed melt convection, and (d) high rotation rates with mixed melt convection [213], The emissivity of the crystal-vapor interface of the system was specified to be 0.3, while the melt-crystal interface emissivity was set to 0.9 for the GGG crystal of refractive index 1.8. Additional property values and geometric details are listed elsewhere [215]. The crucible diameter is 200 mm, the crystal diameter is 100 mm, and thermocapillary convection was not included in the analysis. 

Forced convection cooling can be divided into laminar flow and turbulent flow. The transition from laminar to turbulent flow in air usually occurs at a velocity of 180 ft/min (180 Ifm). In laminar (or sfreamline) flow, the fluid particles follow a smooth, continuous path where the velocity vectors of the particles are always parallel and never intersect. The heat is transferred by molecular conduction in the fluid and by the solid-fluid interface. Tm-bulent flow, characterized by the irregular motion of fluid particles, has eddies in the fluid in which the particles are continuously mixed and rearranged. The heat is transferred in turbulent flow from the eddies back and forth across the streamlines. The greater heat transfer occurs for turbulent flow. 

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