Thank you very much for your response!
How does the heat flux compare between the publication and Fluent?
Heat Flux is not necessarily measured in the experiment, but rather calculated using Q_dot=m_dot * Cp * deltaT. However, the paper does not outline the obtained experimental outlet temperatures. So, I am not too sure how I would approach this. Now with regards to my heat flux measured in Fluent, I followed the link below which was issued by Ansys to measure my heat flux.
This then gives me the Total Heat Transfer Rate at the inlet and outlet of the intermediate tube. If I was to use Q_dot=m_dot * Cp * deltaT, and measure the outlet temperature directly in Fluent I would get similar results to the Total Heat Transfer Rate value.
Total Heat Transfer Rate:
Q_dot=m_dot * Cp * deltaT:
Q_dot = 0.09 [kg/s] * 4190 * (343 - 326.5) = 6278.25
How well refined is the near wall mesh?
I used edge sizing on the pipe edge at the inlet and outlet. This is the only specific mesh sizing method I used.
How did the experiment measure the outlet temperature?
The inlet and outlet temperatures were measured using six shelled precalibrated K-type thermocouples. All thermocouples were connected via a pre-calibrated data acquisition unit (accuracy ±0.01 degC) through computer software.