Droplet properties

The Laser-spin-atomized droplets are usually spherical, clean, and homogeneous in composition. A mass median diameter of 100 pm has been obtained for a Ni-Al-Mo alloy. Cooling rates are estimated to be in the order of magnitude of 105 °C/s. Similarly to other centrifugal atomization techniques, droplet properties (shape, size, cooling rate, etc.) are dependent on the rotation speed, ingot diameter, superheat, and material properties. 

Droplet properties have an important impact on the transport phenomena in associated droplet processes. A thorough understanding of fundamental phenomena, principles and mechanisms in droplet processes is therefore needed in order to enhance efficiency of droplet generation, and to control droplet properties. In this chapter, the mechanisms governing droplet generation and deformation in various droplet processes are reviewed in detail. 

Atomization, or generally speaking droplet generation, is an extremely complex process that cannot yet be precisely predicted theoretically. The lack of general theoretical treatment of droplet processes has led to the development of numerous empirical correlations for droplet properties as a function of process parameters and material properties. In this chapter, empirical and analytical correlations for the prediction of droplet properties, such as droplet size distribution and droplet deformation characteristics will be summarized from experimental observations and theoretical analyses in available literature. 

The fundamental issues to be addressed in the process modeling include spray enthalpy, gas consumption, spray mass distribution, microstructure of solidified droplets, and droplet-substrate interactions. The effects of atomization gas chemistry, alloy composition and operation conditions on the resultant droplet properties are also to be investigated in the process modeling. 

Measurement Techniques for Droplet Properties and Intelligent Control of Droplet Processes... 

Various measurement techniques have been developed and applied with different degrees of success. Some techniques, that are well applicable to the measurement of single droplet properties, find difficulties in the application to measurements of droplet properties... 

In this chapter, the primary measurement techniques for droplet properties are outlined, and their capabilities and limitations are discussed. The approaches to intelligent process control as related to droplet processes are presented along with descriptions of recent developments. 

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