Abstract Earlier ground-based studies have shown that a sharp transition occurs in the dominant mode of heat transport during dendritic solidifcation. Specifically, convective heat transport dominates below the transition supercooling and diffusive heat transport dominates above. Thus the influence of gravitational acceleration on dendritic crystallization depends critically on the overall thermodynamic driving force. Since many practical solidification processes occur at relatively small supercoolings, understanding the nature of the transition in transport mode is essential for both terrestrial and space processing. A boundary-layer analysis has been carried out wherein the diffusion boundary-layer thickness (Stefan length) is compared with the thermal boundary layer thickness determined from the fluid mechanics of natural convection. Our analysis shows that the Stefan length δS decreases rapidly with supercooling (ΔT−2.5) whereas the thermal boundary layer thickness δT decreases slowly (ΔT−.25). The transition supercooling at which the transport mode switches from convective to diffusive occurs where δT = δS. The influence of gravitational acceleration, and the thermo-physical properties of the molten phase will be discussed, along with avenues for conducting future research.
Boundary-layer analysis for the convection/diffusion transition in dendritic growth
Advances in Space Research ; 1 , 5 ; 25-35
1981-01-01
11 pages
Article (Journal)
Electronic Resource
English
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