Heat transfer from the pipe to surroundings

Sir,
We found three options for "Wall Heat transfer" in "Non-Isothermal Pipe Flow" namely
1. Temperature (nitf/nitf)
2. Temperature (nipfl/nipfl)
3. Userdefined. (with an option to check "Take average in adjacent domains)

Can we know what does each of the above mean and what difference it is going to do to the heat transfer from the flow through pipes??