Air Entrapment Under a Liquid Drop Impacting on to a Solid or Liquid Surface

الموضوعات

علوم تطبيقية وتكنولوجية

الملخص

Drop impacts are present in our everyday lives, from showering and washing the dishes to inkjet printing and many industrial processes, such as spray coatings and spray cooling. In many of these applications it may be undesirable to have air entrained within the drop when it impacts a surface. As a drop approaches a surface, the gas beneath the drop is unable to fully escape resulting in a rising pressure which becomes sufficient to form a dimple in the bottom center of the drop. Therefore, when the drop makes contact with the surface, it is around the perimeter of this dimple, thus entrapping a disc of air which contracts into a minute bubble.In this dissertation, we study the very early time dynamics of the formation of the central air disc under a variety of circumstances using ultra-high-speed interferometry at rates up to 5 million frames per second. We show the effects of the liquid viscosity for viscosities spanning 7 orders of magnitude, for impacts of drops onto solid surfaces or a film of the same liquid. We find that the size of the air disc is weakly dependent on the drop viscosity to the -1/9 power. We also explore the extended gliding of the drop on a less than 160 nm thick film of air. For impacts onto a solid surface, this gliding layer is rupture in multiple random locations and each localized contact wets the surface at extreme rates compared with the expected viscous-capillary velocity. For impacts onto liquid films, the localized contacts are rarely observed and the gliding layer ruptures at a uniform location. The central bubble contracts much faster than expected in this case as well.Furthermore, we study the effects of reducing the ambient air pressure discovering a compressible and rarified-gas regime wherein the drop makes a double contact with the surface. Lastly, we study the effects of nano-scale surface roughness on the central bubble and the formation of thick bands of microbubbles around the periphery of the air disc.

روابط وملفات

التعريف والنوع

رقم الوثيقة

fcc4e986-59cf-4d45-a6e9-8be0dc994b44

رقم العقد

0

نوع الوسائط

Crawler

نوع المحتوى

الرسائل العلمية

صيغة المصدر

رسائل دكتوراة

نوع الملف

pdf text

أسماء الملفات

1698400_1.pdf

بيانات النشر

ألقاب المؤلفين

[{"name_ar":"Langley, Kenneth","title_ar":"اعداد","title_en":"Preparation"},{"name_ar":"Thoroddsen, Sigurdur T","title_ar":"اشراف","title_en":"Supervision"}]

اللغة

English

المصدر والدورية

اسم المصدر

Air Entrapment Under a Liquid Drop Impacting on to a Solid or Liquid Surface

المحتوى والصفحات

عدد الصفحات

0

كلمات الباحثين

drop impact , high viscosity , high-speed imaging

إشراف وإعداد

الإشراف

Thoroddsen, Sigurdur T

الإعداد

Langley, Kenneth

الاقتباسات الببليوغرافية