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Архив
Proceedings of the 24th National and 2nd International ISHMT-ASTFE Heat and Mass Transfer Conference (IHMTC-2017)


ISBN Онлайн: 978-1-56700-478-6

STABILITY OF TEARDROPS-EFFECT OF EVAPORATION

DOI: 10.1615/IHMTC-2017.1070
pages 759-763

S S Jayakrishnan
IIT Hyderabad

Atul S Vivek
IIT Hyderabad

Harish N Dixit
Indian Institute of Technology Hyderabad, Telangana

Аннотация

The stability of precorneal tear-films have been a topic of great research interest owing to its critical role in preventing pathological conditions of the ocular surface. For a healthy person, the tear film undergoes rupture within 15-40 seconds if the eye is kept open and it is the involuntary blinking that helps in re-establishing the structural integrity of the tear film But abnormalities in tear film can lead to its rupture much earlier than the inter blink period of 5-10 second, exposing the cornea to a host of pollutants and pathogens. For effective diagnosis and treatment of Dry-Eye syndrome, the accurate estimation of tear film break-up time is of paramount importance. While there are clinical procedures to estimate the rupture time, the variability caused by atmospheric conditions such as humidity and temperature changes pose a significant challenge in standardizing these clinical observations. In this paper, we propose a model for the tear film that accounts for these variations in surroundings and assess its impact on the rupture time estimates. Generally, the tear film is thought to be composed of three layers - aqueous layer which constitutes the bulk of the tear film, a mucin layer below the aqueous which separates the latter from the corneal epithelium, and a top-most lipid bilayer which is believed to function not only as a surfactant mono layer that reduces the interfacial tension between the aqueous layer and the atmosphere but also as a barrier that reduces evaporative mass loss. For the sake of simplicity, in this paper we model the tear-film as a single layered thin-film laden with insoluble surfactants and study the effects of temperature changes on its stability. Following the works of [1], van der Waals interaction between the interfaces is put forward as the driving cause of film rupture while viscous retardation, surface tension and Marangoni convection are expected to slow down rupture. In addition to this, from the work of [2], we also propose evaporation occurring from the tear-film surface as the chief mechanism to incorporate variability due to atmospheric conditions. From the works of [3] and [4], the combined effect of surfactant and evaporation on the thin film is used for finding out the stability of tear-films