No worries, that means I'll just use the mass-weighted average method when extracting the outlet temperature from now on. Thanks for this!
Apologies if my problem definition is unclear. I have three fluid annular flow paths as there are three channels within the triple concentric tube heat exchanger. Hopefully, the figure below would provide a better description of the system.
The system setup is as follows:
- Hot Fluid flows through the middle tube (70degC) --> main heat transfer fluid
- Cold fluid flows through the inner tube (10degC)
- Normal fluid flows through the outer tube (18degC)
The aim of this project is to show that a triple tube heat exchanger has better heat transfer properties compared to the conventional double tube heat exchanger due to its larger heat transfer area. In a double tube heat exchanger, heat is transferred from the hot fluid to the cold fluid via convection and conduction through the pipe wall. On the other hand, in a triple tube heat exchanger, the hot fluid flows through the intermediate tube. This allows the heat to be transferred to the normal temperature fluid in the outer tube, and to the cold temperature fluid in the inner tube. This way, the heat transfer rate would be increased due to the increased heat transfer area.
Hence, to answer your question of how do you account for heat entering the middle one from the outer as compared to the inner? I am not too sure if this would be an area of concern of mine. Theoretically, heat would only be transferred from the middle tube to the outer and inner tubes. If there is heat transferred from the lower temperature medium to the higher temperature medium, I think this would be relatively minimal and hence could be neglected. Please do correct me if my understanding is incorrect.