Sharif University of Technology Scientia Iranica 1026-3098 17 2 2010 04 01 Three-Dimensional Simulation of Turbulent Flow in 3-Sub Channels of a VVER-1000 Reactor 3252 EN B. Firoozabadi Department of Mechanical Engineering,Sharif University of Technology H. Ganjiani Department of Mechanical Engineering,BUET Journal Article 2010 04 27 In this study, the uid dynamics and convective heat transfer for turbulent ows through a 3-sub channel of a rod bundle, which is representative of those used in VVER-1000, are examined. The rod bundle is constructed from parallel rods in a hexagonal array. The rods are on constant pitch by spacer grids spaced axially along the rod bundle. The geometry details of the bundle and heat ux from the fuel rod are similar to that of the Iranian nuclear reactor under construction. A numerical study using Computational Fluid Dynamics (CFD) was carried out to estimate the ow eld, pressure loss and heat transfer coecients in spacer grids and rod bundles. Turbulence has been modeled using the k ???? " turbulence model. At a distance of 2Dh from the beginning of the spacer grids, in the direction of ow, because uid enthalpy and Nusselt numbers have maximum and minimum values, respectively, the probability of nucleate boiling (PNB) is much higher, and a two phase ow will occur. Predicted results are found to be in close agreement with those of the experimental results reported in the literature. https://scientiairanica.sharif.edu/article_3252_eaec0569bcb25658931d11d38fb7d388.pdf