Accessing the outlet value to apply in the inlet boundary

Hi.

I need to set up the inlet boundary condition (temperature) in the conjugate heat transfer analysis with larminar flow. However T of inlet (fluid) should be like this:

Tin = Tout + 3 K (at every time step)

The scenario is that the water from outlet is boiled and then re-injected into inlet.

What variable do I use to get outlet temperature?

Is there any function to access boundary values in the variable expression?

Thanks.

Chulho