Buoyancy and Thermal Acceleration of Supercritical n-Decane in a Rectangular Channel

In this work, supercritical n-decane flowing in ducts with different orientations is thoroughly investigated in terms of secondary flow, wall shear stress, and thermal acceleration. It is known that the secondary flow strength hardly plays a role in cases of flowing upward, flowing downward, or flowing horizontally at a small heat flux/mass flux. Still, an attachment point can be found at the center for cases of flowing upward and flowing downward, and this enhances the heat transfer. For a large heat flux/mass flux, thermal transport depends not only on the secondary flow strength but also on the secondary flow structure. Besides, a separation point is found at the center for flowing up/downward cases, and the more adjacent the attachment point is to the heated wall, the more serious is the thermal transport. The wall shear stress is beneficial to heat transfer but also relies on the distribution profile. Thermal acceleration can really diminish or even restrain the HTD phenomenon, but it is not the reason to cause the difference of heat transfer behavior for channels with different orientations.