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The Effect of Tear Film on Ocular Surface Temperature: A Thermodynamic Study

[+] Author and Article Information
Jen Hong Tan

Department of Electronics and Computer Engineering,
Ngee Ann Polytechnic,
Singapore 599489

E. Y. K. Ng

School of Mechanical and Aerospace Engineering,
College of Engineering,
Nanyang Technological University,
50, Nanyang Avenue,
Singapore 639798
e-mail: mykng@ntu.edu.sg

U. Rajendra Acharya

Department of Electronics and Computer Engineering,
Ngee Ann Polytechnic,
Singapore 599489;
Department of Biomedical Engineering,
School of Engineering,
University of Malaya,
Kuala Lumpur 50603, Malaysia

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 29, 2012; final manuscript received January 17, 2013; published online April 11, 2013. Assoc. Editor: Giulio Lorenzini.

J. Heat Transfer 135(5), 054505 (Apr 11, 2013) (5 pages) Paper No: HT-12-1320; doi: 10.1115/1.4023543 History: Received June 29, 2012; Revised January 17, 2013

The thermodynamic effect of tear film on ocular surface remains ambiguous in literature, though in general it is considered to warm the surface in blinking phase, and cool it at later stage. In this investigation, we modeled the temporal variation in ocular surface temperature (OST) on the basis of Newton's law of cooling to look into the tear film's thermodynamic effect. We assumed, the OST varied periodically and the OST just before a blink was equal to the OST observed when the surface was in equilibrium. Then, this model was incorporated into a thermodynamic equation, describing the heat exchange at the ocular surface. Simulations were subsequently performed to determine the moment when the tear film evaporated the exactly amount of energy it had just brought to the surface by blinking in an interblink period. It was found that, for tear film to possibly warm the ocular surface both in the blinking phase and the entire interblink period, its thickness had to be above 32 μm, assuming the rate of spontaneous blinking was once per 6 s. However, according to literature, tear film thickness is likely to be 3 μm, which in this case, the tear film would evaporate the tear-transferred heat just within a second, and the warming effect by tear film would be minimal; cooling should be the dominating effect.

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References

Figures

Grahic Jump Location
Fig. 3

Simulation performed under the second set of conditions where E[T(x,y,0)] = 35.4°C, E[T(x,y,∞)] = 35.2°C, Tb = 37 °C, and Tamb = 25.5 °C

Grahic Jump Location
Fig. 4

Simulation performed under the third set of conditions where E[T(x,y,0)] = 32.0°C, E[T(x,y,∞)] = 31.2°C, Tb = 37 °C, and Tamb = −10 °C

Grahic Jump Location
Fig. 2

Simulation performed under the first set of conditions where E[T(x,y,0)] = 35.7°C, E[T(x,y,∞)] = 35.4°C, Tb = 37 °C, and Tamb = 25.5 °C

Grahic Jump Location
Fig. 1

The control volume (a small piece element) and its corresponding heat exchange

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