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Optical Fiber Heat analysis

I am conducting a thermal analysis of optical fibers. ( Software used AutoCAD Fusion 360)

The Inputs conditions are :

Let's assume an input power of 1250W, with an efficiency of 98%. 2% loss which becomes heat. (25W)

The internal heat of 25W at the inner core ( power loss ) gives 407.7 degrees Celcius.

Convection Coefficient of $10W/m^2K$ (Convection of still air)

The material of the rod I assume is glass with an emissivity of 0.9 ( Radiation ).

The temperature of the optical fiber reaches 407.7 degrees Celcius, which is inconsistent with real life. The temperature should be approximately 35 degrees Celcius? Why is this so, am I missing out on another method of heat loss? Any help will be greatly appreciated.

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If you increase the length of the fibre, you will get more reasonable results. The losses -in my mind- need to be distributed along the entire length of the fiber .

Currently, you seem to model a very small portion of the fiber, and as such you have a very small area that need to transfer a seemingly small amount of energy. However, if that energy is going through a small surface area then the energy over area is high and therefore the end temperature difference will need to be high.

Another way you can approach it, is that you can you can adjust the heat losses. I.e. if you have a 1m of fiber, and you model 0.1 m , then instead of 25 W you can use 2.5 watts (provided everything else in the model is correctly setup).

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    $\begingroup$ Correct: the loss has to be expressed in energy (or power) per unit length, just as the fundamental absorption constant is. $\endgroup$ Sep 2 at 15:42

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