Hello,I think this heatexchanger is not made for those big temperature differences. Usually these devices are designed for minimum temperature loss and so they are optimized for low thermal resistance.
The steam inlet in Rossis configuration has 100° or more. The warm water outlet has 30° or less.There must be considerable heat conduction along the hot tube and without doubt this will give a temperature gradient along the tube. Therefore the thermocouple temperature will be some degrees hotter than the water temperature.
Rossis argumentation is valid only if the exchanger is operated inside a normal operation, but this application is not normal and heat gradients along the brass-tube must be considered. It is hard for me to explain what I mean in english words, but I made a simple drawing that should clarify what I mean.
The drawing is appended. Note, the temperatures given are examples and not actual values. Kind regards, Peter
<<attachment: Hexchange1.png>>
