[erginbayrak]

We have been numerically investigating the thermal-fluid characteristic of sCO2 laminar flowing in a 0.5 mm diameter circular microtube in upward direction. Depending on sharp density change along the tube, this case can be admitted as a compressible flow. When applied pressure-based solver option, the pressure firstly decreases until a certain point along the tube, then increases towards the outlet. So, this situation is impossible. Although the entire graph is very reasonable, the pressure change along the flow direction is interesting as seen in the attached file. When calculated theoretically (considered friction depending on both wall shear and momentum change) by using Ansys data (wall shear stress, density, axial velocity, etc.), the pressure drop is found as expected (full decreasing along flow direction).