Measurement of post dryout heat transfer coefficient in a double heated annulus with flow obstacles

An experimental study on post dryout heat transfer regime in annuli with flow obstacles was conducted in the High-pressure Water Test (HWAT) loop at the Royal Institute of Technology in Stockholm, Sweden. The experimental investigations were performed in a wide range of the operational conditions: mass flux (500-750) kg/(m²s), inlet subcooling (10-40) K and system pressure (5-7) MPa. The wall superheat was measured at 88 different axial and azimuthal positions (40 on the inner tube and 48 on the outer tube). The results show an enhancement of heat transfer downstream of flow obstacles. The biggest influence has been observed in case of pin spacers and grid obstacle. This result is consistent with blockage area of various obstacles, which was the highest in case of pin spacers. (author)