Interface connection between domains
 

The geometry has four domains in concentric tube

• Inner most - Fluid 1
• Adjacent to inner - Solid
• Adjacent to Outter most - Fluid 2
• Outter - Solid

The geometry is created by crating four material points.

How to define BC at the interfcae for fluid flow and heat transfer ?. There is no mass transfer as both the fluids are isolated.

This sounds like a straight forward CHT simulation. Have a look at the tutorial examples - the resistance heater one will be relevant to you.