ICONE19-43492 STUDY OF SELECTED TURBULENT MODELS FOR SUPERCRITICAL WATER HEAT TRANSFER IN VERTICAL BARE TUBES USING CFD CODE FLUENT-12

Many of the available empirical correlations existing today cannot predict closely the effects of the heat transfer phenomena within the pseudocritical region, and some do not predict well enough heat transfer coefficients even outside of this region. In this study, the Computational Fluid Dynamics (CFD) code FLUENT-12 is used with associated software such as Gambit and NIST REFPROP to predict the Heat Transfer Coefficient and corresponding wall temperature profiles inside circular tubes cooled with SuperCritical Water (SCW), and to compare them with experimental data and various empirical correlations. In this paper, a numerical study of heat transfer to SCWflowing upwards in vertical bare tubes using the CFD-code FLUENT-12 is presented for comparison to 1-D models. A large dataset was collected within conditions similar to those of proposed SuperCritical Water-cooled Reactors (SCWRs) at the Institute for Physics and Power Engineering in Obninsk, Russia. This dataset includes 80 runs in a 4-m long, 10-mm ID vertical bare tube within a wide range of operating parameters including pressure at about 24 MPa, inlet temperatures from 320 to 350℃, mass flux ranges from 200 to 1500 kg/m^2s and heat fluxes up to 1250 kW/^m2. Wall and bulk-fluid temperatures measured along the 4-m heated length test section were below, at, or above the pseudocritical point. Further analysis of the individual heat-transfer regimes was conducted using an axisymmetric 2-D model of a tube with 10,000 nodes along the heated length. Wall temperatures and heat transfer coefficients were analysed for 1-m sections at a time to select the best model for each region (below, within and beyond the pseudocritical region), and to neutralize effects of the rest of the tube on that region. Two turbulent models were used in the process: k-ε and k-ω, with many variations in the sub-model parameters such as viscous heating, thermal effects, and low-Reynolds number correction. The results show a good fit within the most low/mid range operating conditions with noticeable deviations within the high range, primarily at the deteriorated heat-transfer regime with an overall better fit for the k-ε model.