Experimental investigation of post-dryout heat transfer in annulus with spacers

Experimental investigations of post-dryout heat transfer in 10 × 22.1 annulus test section with spacers were carried out in the high-pressure two-phase flow loop at the Royal Institute of Technology (KTH). The test section was manufactured of Inconel 600 to withstand high temperatures. Several thermocouples were installed on tube and rod surfaces to measure the local wall temperature. Measurements were performed for mass flow rate in range from 500 to 2000 kg m⁻² s⁻¹, with inlet subcooling equal to 10 and 40 K, heat flux in a range from 480 to 1380 kW m⁻² and for the system pressure of 7 MPa. Uniform axial power distributions were applied on rod and tube walls. Using different distributions of heat flux between walls, post-dryout was achieved either on the inner or on the outer wall. The experimental results indicate a very strong influence of spacers on post-dryout heat transfer. For low mass flow rates the wall superheat was significantly reduced downstream of spacers, even though the whole distance between spacers was still under post-dryout conditions when heat flux was high enough. At high mass flow rates and under investigated range of heat flux the dryout patches were effectively quenched downstream of spacers.