Experimental study on heat transfer to supercritical and near-critical water in a three-rod bundle with spacer grids

Heat transfer experiments of supercritical and near-critical water flowing in a three-rod bundle with spacer grids are performed at Shanghai Jiao Tong University. The test section consists of three heated rods and three unheated rod-like elements with an outer diameter of 15 mm and a pitch to diameter ratio of 1.2. The effective heated length is 1500 mm. The test conditions are as follows: pressure ranging from 20 to 23 MPa, mass flux varying from 800 to 1600 kg/(m² ·s), heat flux between 400 and 700 kW/m² and bulk temperature ranging from 285 to 380 ℃ Non-uniform circumferential wall temperature distributions are observed and analyzed respectively in different heat transfer regions. Parametric effects of mass flux, heat flux and system pressure on heat transfer are discussed. Especially in subcooled and saturated boiling regions, due to the occurrence of heat transfer deterioration, heat flux plays an opposite role compared to that under normal conditions. In addition, a CFD verification is carried out with various turbulence models, among which SST k-ω model shows the best performance and agrees well with the test data.