NUMERICAL INVESTIGATION OF HEAT TRANSFER TO SUPERCRITICAL WATER IN A 2 x 2 ROD BUNDLE WITH TWO CHANNELS

In the present study, a numerical investigation was made using the ANSYS Fluent code to analyze the heat transfer to supercritical water in a 2 X 2 rod bundle. The geometry consists of two channels separated by a solid body. Water moves downward in the first channel and then moves upward in the second channel, which is connected through U-turns. This results in cooling of the rod bundle, which is stationed in the second channel. The outer diameter of the heated rod is 10 mm. Two turbulence models, i.e., k-epsilon (RNG) and k-omega (SST), were benchmarked against the experimental data. It was found out that the k-omega (SST) model gives the best prediction for heat transfer as well as for the wall temperature distribution in supercritical water with an error maximum of up to 6.8% for the heat transfer coefficient. A parametric study was carried out by the variation in the wall heat flux, mass flux, and operating pressure to study their effects on heat transfer. The results show that the heat transfer phenomenon is similar to that found in a simple tube. A comparison of the heat transfer coefficient with the Dittus-Boelter equation was made and was used for normalizing the predicted heat transfer coefficient. Three heat transfer regimes were observed, namely: normal heat transfer, enhanced heat transfer, and deteriorated heat transfer. The onset of heat transfer deterioration was predicted for a mass flux of 350 kg/m(2).s, which shows lower values of the heat transfer coefficient ratio. It was observed that the effect of buoyancy was prominent near the pseudocritical region, after which its effect faded out.