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ISSN Druckformat: 1044-5110
ISSN Online: 1936-2684
Indexed in
PRESOLIDIFICATION LIQUID METAL DROPLET COOLING UNDER CONVECTIVE CONDITIONS
ABSTRAKT
A model investigating the heat and fluid flow fundamentals of liquid metal droplet cooling during spray deposition processes is presented. The droplet configuration studied involves a laminar, axisymmetric gaseous flow around a spherical, superheated, all-liquid, pure metal droplet, which initially has no internal motion and a uniform temperature before it is injected with zero velocity into a cool, uniform gas stream. This flow configuration is identical to one where the droplet is injected into a quiescent gas with a specified velocity. A detailed solution approach is adopted in both gas and liquid phases, even though the temperatures within typical liquid metal droplets are expected to be almost uniform. However, the establishment of temperature differences of even a few degrees in the droplet interior would create very high temperature gradients, given the small sizes of the droplets. High temperature gradients, in turn, have a strong influence on solidification, with a decisive effect on the material properties of the solidified substance. The model, which accounts for variable thermophysical properties in the gas phase, transient droplet cooling with internal liquid circulation, and droplet deceleration with respect to the free flow due to drag, produces time-varying spatially resolved data for the entire flow field in the vicinity of the droplet. These results provide information on the fundamental processes governing the energy and momentum exchange between the droplet and the gaseous stream. The laminar flow simulations for a liquid aluminum droplet at atmospheric pressure show that temperature gradients of the order of 25,000 K/m are maintained in the droplet interior throughout the droplet flight. These gradients are very significant for the subsequent onset of solidification, which has not been modeled in this study. In addition, the relatively high convective cooling rates achieved (> 105 K/s) are enhanced by reduced ambient pressures. The model predictions for the droplet drag coefficient and Nusselt numbers are compared with the values obtained through widely used correlations for the evaluation of these quantities in more populous metal sprays.
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Xiong B., Megaridis C. M., Poulikakos D., Hoang H., An Investigation of Key Factors Affecting Solder Microdroplet Deposition, Journal of Heat Transfer, 120, 1, 1998. Crossref
-
Henein Hani, Single fluid atomization through the application of impulses to a melt, Materials Science and Engineering: A, 326, 1, 2002. Crossref
-
Chang Keh-Chin, Chen Chih-Ming, Revisiting heat transfer analysis for rapid solidification of metal droplets, International Journal of Heat and Mass Transfer, 44, 8, 2001. Crossref
-
Poulikakos Dimos, Waldvogel John M., Heat Transfer and Fluid Dynamics in the Process of Spray Deposition, in Transport Phenomena in Materials Processing, 28, 1996. Crossref
-
Wiskel J.B., Henein H., Maire E., Solidification Study of Aluminum Alloys using Impulse Atomization: Part I: Heat Transfer Analysis of an Atomized Droplet, Canadian Metallurgical Quarterly, 41, 1, 2002. Crossref
-
Fritsching Udo, Spray Simulation, 2004. Crossref