CFD Study on Specifics of Flow and Heat Transfer in Vertical Bare Tubes Cooled With Water at Supercritical Pressures

Abstract

The paper presents results of a study on flow and temperature fields in bare tubes cooled with SuperCritical Water (SCW). This study is based on a Computational Fluid Dynamics (CFD) simulation with the FLUENT code for upward flows in vertical tubes with heated length of 4 m and an inner diameter of 10 mm. Operating conditions were: Mass flux – G ≈ 500 and 1000 kg/m2s; heat flux – q = 189 – 826 kW/m2; and inlet coolant temperature – Tin = 320–360°C. CFD predictions were compared with experimental data in this study. All three heat-transfer regimes: 1) normal heat transfer; 2) improved heat transfer; and 3) deteriorated heat transfer; were considered. The obtained results show that within normal and improved heat transfer CFD predicts experimental values reasonably well. However, within conditions of deteriorated heat transfer CFD predictions are less satisfactory. The CFD outcomes of the heat flux effect on the flow and heat transfer of SCW are presented. Specifics of flow within the pseudocritical region (i.e., approximately ±25°C around a pseudocritical point) are discussed. The buoyancy effect is investigated by axial velocity profiles at the medium mass flux of 500 kg/m2s and heat flux of 287 kW/m2.