Numerical study of conjugate heat transfer of steam and air in high aspect ratio rectangular ribbed cooling channel

The relationship between flow field and heat transfer in an air/steam cooled ribbed channel was numerically investigated and compared. The width to height ratio was 4 and the rib height to hydraulic diameter was 0.078. The conjugate heat transfer method was adopted and a uniform heat source was located in the solid domain to simulate the actual heating method in the experiment. The GGI method was used to deal with the solid-fluid interface. The fluid field structure was shown by vortex core technology. We found that the wall heat flux distribution is similar with that of the Nusselt number, which is periodic. The temperature difference of a certain position on the inner and outer wall was less than 2 K. The Nusselt number reached its peak value at No.15-18 part and then decreased. The large width to height ratio led to strong interaction between the main flow fluid and the fluid in near wall region. As a result, an extra main flow secondary flow and two separation vortexes could be observed. These three additional vortexes were all in main flow region. The two separation vortexes approached to each other in flow direction and mixed into one vortex at low Reynolds number. When Reynolds number is larger than 30000, the two vortexes remain independent. The relative distance between them reaches the minimum value and the Nusselt number reaches the peak value at the same time. In addition, the flow field structure is mainly determined by Reynolds number and the fluid type cannot obviously influence the secondary flow distribution. The generation and separation of secondary flow as well as the mixing of secondary flows can enhance the local heat transfer strength.