Film surface interaction on a wire in a three dimensional volume for heat transfer analysis

[m0lind04]

Hello everyone,
I am looking for a possibility to avoid applying a film surface condition (interaction with film coefficient and sink temperature) on a small opening in a large volume of soil, due to increasing the complexity of the mesh.
Rather I would like to generate a wire part in the volume of soil, add a section to the wire, which then allows me to apply a film surface condition on it. That way I am hoping my mesh will not generate the typical small elements around an opening but just connect to the wire.
I know how to create a wire, apply different sections, etc.. but I am running into problems, since there is no actual surface generated to apply the interaction on. Even by applying a BC with a constant temperate to the wire, it only generates a heat flux/temperature influence to the soil volume at the start and end nodes of the wire.
Any ideas/help?
Thank you.

 

[FEA way]

I would use submodeling instead of beam elements for this purpose. You can create a model of small region around the opening and utilize submodeling technique so that this region will be analyzed separately with BCs that prescribe solution variables from the global model. That way you don't have to solve the whole model again.