Abstract
Dryout and post-dryout heat transfer experiments in a tight three-rod bundle with spacer grids are carried out at Shanghai Jiao Tong University. The test section is made up of three heated rods with an outer diameter of 15 mm and three unheated components. The pitch-to-diameter ratio is 1.2. The heated length is 1500 mm. The working conditions are given as follows: pressure varying from 6 to 10 MPa, mass flux ranging from 65 to 200 kg/(m2·s), heat flux between 75 and 200 kW/m2. The dryout almost occurs simultaneously in the circumferential direction of the heated rod and the varying trend of wall temperatures along the axial direction are similar. The effects of mass flux, heat flux and system pressure on the dryout quality are discussed and analyzed respectively. The comparison of the empirical correlations and the experimental results indicates that a more accurate prediction method of the dryout quality in the rod bundle is needed. Meanwhile, non-uniform circumferential wall temperature distributions are observed in the bundle. The wall temperatures in the directions towards the gaps between heated rods are higher and those in the directions towards the center areas of subchanels are lower. What’s more, the un-uniformity of wall temperatures is founded to be significantly affected by the spacer grids.
