Numerical analysis of in-flight freezing droplets: Application to novel particle engineering technology

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Abstract

The freezing of a stream of free-falling monodispersed droplets was simulated through the development of numerical models in this work. Prediction of the freezing time and temperature transition of a single droplet is beneficial for optimisation of novel continuous spray freeze drying (cSFD) processes. Estimations of the vertical free-falling distance of the droplets in a slip stream and predictions of the chances of droplet coalescence greatly enhance process understanding and can be leveraged to direct equipment design and process development. A design space of droplet diameters in the range from 100 μm to 400 μm and ambient temperatures from −120 °C to −40 °C was explored. The rate of supercooling within the design space was predicted to range from 48 to 830 °C s −1 depending on the ambient temperature and droplet size. A comparison of the vertical free-falling distances of solitary droplets and streams of droplets at different temperatures showed that the terminal velocity of a vertically falling stream of droplets is always in excess of the terminal velocity of a solitary droplet of the same size. A difference of 1.35 m was predicted for the free-falling distance of a 400 μm droplet compared to a stream of droplets at −42 °C. A comparison between flow rates for consecutively generated 100 μm droplets showed that droplet coalescence was predicted at 0.05 Lh −1 , whilst at 0.02 Lh −1 a separation distance of 23 μm was maintained thus preventing coalescence.

Original languageEnglish
Pages (from-to)30-40
Number of pages11
JournalFood and Bioproducts Processing
Volume116
Early online date27 Apr 2019
DOIs
Publication statusPublished - 1 Jul 2019

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