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Understanding the Nuances of Spray-freezing Process
Published in S. Padma Ishwarya, Spray-Freeze-Drying of Foods and Bioproducts, 2022
Nevertheless, during SFL, boiling-off of cryogen can occur due to the heat introduced by the relatively warm feed jet from heated nozzles. The above phenomenon is termed as the Leidenfrost Effect, which causes some droplets to encounter lower cooling rates owing to the insulating effect of boiled-off vapor around them. This effect prolongs the phase of ice crystal formation due to low thermal conductivity, resulting in low freezing rate (Engstrom et al., 2007; Wanning, Süverkrüp, & Lamprecht, 2015). Leidenfrost effect was found to be prominent while using liquid nitrogen as the cryogenic liquid. But, the same was not observed with iso-pentane due to its significantly higher boiling point (27°C) and larger heat of vaporization and thus the low tendency to evaporate (Engstrom et al., 2007). Thus, iso-pentane is a more appropriate cryogenic liquid for SFL as it can be cooled down to −160°C before it freezes (Ishwarya, Anandharamakrishnan, & Stapley, 2015).
Receding Dynamics of Jatropha Straight Vegetable Oil Drops Impacting a Heated Surface
Published in Heat Transfer Engineering, 2022
Vikas Kumar, Amrit Kumar, Deepak Kumar Mandal
A large number of applications of drops impacting heated surfaces demand operation below the Leidenfrost point. Examples include fuel – wall interaction in fuel combustor [2–9], spray cooling [10–13], thermal spray coating [14], inkjet printing [15, 16], fire extinguishing [17], cooling of solar panels [18], and lubrication [19, 20]. In most of the applications, the impact above the Leidenfrost point is unwanted and can be even detrimental in a few cases. For example, the Leidenfrost effect and film boiling reduce spray cooling efficiency due to the reduced contact time resulting in lower heat transfer.