An external surface temperature is introduced, and the LMTD is calculated in reference to this temperature. It is necessary to take into account that, except if we can grant really an unique surface temperature, the objetive of this calculation is not to obtain the exchanged heat, but to obtain a surface temperature for introducing corrections in the calculation, once the heat transfer is known. In this case the heat transfer is calculated using information from both sides.
It adds also an optional heat port, in order to allow the connection of the pipe to other thermal elements. As the connector gives only one temperature and one heat flow, the use is limited.
.FreeFluids.Pipes.PipeThermalBase