| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系 === 84 === The first part of this study regards the accelerating
effects on motion ofdroplet. It was found that the drag
coefficients of the droplets travelling in aflow field were
usually underestimated by using its steady form. This is
attributedto the neglect of the accelerating effects in the
fformation of drag coefficient.In the study, a case of simple
evaporating droplet is investigated. Improvedpredictions are
obtained by considering the accelerating effects in thedrag
coefficient. In addition, the accelerating effects become more
significantas for larger droplets. The second part of this
study regards the solidification process of single droplet. Due
to the following advantages:quick solidification state,low
oxidationextent,micro-segregation,fine grain and less steps in
the manufacturing process,the spray forming technique becomes a
potential method for production ofadvanced alloys. As in the
spray forming process,liquid metals are atomized first.
Theliquid-metal droplets are then cooled and solidified through
surrounding gas.Investigations of solidification process of a
liquid-metal droplet in free fallingcondition is made through
different numerical models. It is concluded that the assumption
of lumped system deems reasonable for the small-size droplets
usuallyencountered in spray forming. Supercool phenomena is also
considered throoughthe concept of nucleation.
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