Heat transfer to supercritical water in a 2 × 2 rod bundle

An experimental study on heat transfer to supercritical water flowing in a 2 × 2 rod bundle test section with two channels is carried out at Shanghai Jiao Tong University. The bundle consists of four heated rods with an OD of 10 mm and a pitch-to-diameter ratio of 1.18. The 2 × 2 rod bundle is inserted 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 23 to 26 MPa, mass flux ranging from 400 to 1200 kg/m2 s, heat flux between 300 and 1000 kW/m2, and bulk fluid temperatures ranging from 200 to 480 °C. The heat transfer through the assembly box is strongly affected by the temperature difference between the two channels. The minimum fluid enthalpy increase in the first channel appears near the pseudo-critical temperature region. Non-uniformity of circumferential wall-temperature distribution around the heated rod is observed. The effects of various parameters on heat transfer behavior inside the 2 × 2 rod bundle are similar to effects observed in tubes. Six developed correlations are compared with the test data. The correlations of Jackson and Fewster (1975) and Bishop et al. (1964) provide the best predictions of the test data among the selected correlations.