An experimental investigation on heat transfer of supercritical water and transient heat transfer during pressure drop from supercritical to sub-critical conditions in a 2×2 bundle with two channels has been carried out on the supercritical water multipurpose test loop II (SWAMUP-II). The bundle consists of four heated rods with an O.D. of 10 mm and a pitch-to-diameter ratio of 1.18. The 2×2 bundle with wire wrap is installed into a square assembly box with rounded corners by which the test section is separated into two channels. Water flows downward in the first channel between the pressure tube and the assembly box, and then turns upward in the second channel inside the assembly box to cool the four heated rods, which are directly heated by DC power. The experimental conditions are as follows: pressure ranging from 16 to 26 MPa, mass flux from 400 to 1450 kg/m2s, heat flux from 250 to 1000 kW/m2, bulk temperature from 280 to 500 °C, and pressure drop rate of 1 and 2 MPa/min. The experimental data are obtained and heat transfer characteristics discussed.
