Experimental study on heat transfer of supercritical water flowing upward and downward in 2 × 2 rod bundle with wrapped wire

Heat transfer to supercritical water flowing upward and downward in a 2 × 2 rod bundle with wrapped wire was experimentally investigated. The rod bundle consists of four heating rods within out-diameter of 10 mm. The rods are arranged in a 2 × 2 square array and the pitch-to-diameter ratio is 1.18. The bundle is inserted into a square assembly box with round corners. The water as coolant flows upward or downward in the channel between the rod bundle and the assembly box. The pressure ranges from 23 to 26 MPa, mass flux ranges from 450 to 1200 kg/(m2 s), heat flux ranges from 200 to 1000 kW/m2, and the fluid temperature ranges from 200 to 450 °C. The effects of system parameters including mass flux, heat flux and pressure on the heat transfer are presented, respectively. The heat transfer deterioration occurs at a low G/q ratio in the upward flow, but does not appear in the downward flow. Watts-Chou correlation and Bishop correlation give the best predictions when evaluated against the experimental data both in the upward and downward flow. The experimental data are compared with the bare rod bundle. The comparison indicates that the swirl flow of wrapped wire promotes the heat transfer in the rod bundle.