Reply To: Having issue with Film coefficient.

[Bhargava Sista]

Uday,

The film coefficient or the heat transfer coefficient is the proportionality constant between the heat flux and the temperature difference. This value differentiates the properties of the surrounding fluid, for instance, heat flux would be different for stagnant air compared to flowing air or static/moving water. So, this depends on the nature of fluid to which the system is losing its heat to.

In your case, if the rail is losing its heat to surrounding air, you'll need to find the appropriate value. Here's a link where they have listed the heat coefficient values for some scenarios. 

http://thermopedia.com/content/660/

For your case, you may either go with free convection to air at 30 degrees C (5 W/m^2-K), or forced convection at low speed of airflow over the surface (10 W/m^2-K).