Improvement on numerical simulation of supercritical water flow in horizontal tubes: A buoyancy-tuned turbulent Prandtl number model

Abstract

To improve the predictive accuracy of numerical simulations for supercritical water, the effect of turbulent Prandtl number (Pr_t) on supercritical water heat transfer was extensively studied using the Shear-Stress Transport (SST) $k-\omega$ turbulence model. The efficacy of typical turbulent Prandtl number models for predicting heat transfer in horizontal tubes with supercritical water was evaluated based on wall temperatures measured experimentally and fluid temperatures obtained from multi-point temperature measurement devices. These models successfully demonstrated the phenomenon of thermal stratification due to physical property variations, but their predictive performance near the pseudocritical temperature, particularly in the top wall region, was not satisfying. Building upon this, the supercritical water buoyancy-tuned turbulent Prandtl number model (SWBT model) suitable for supercritical water in horizontal tubes was developed through coefficient calibration and the integration of buoyancy correction terms to ensure accuracy and applicability. This model effectively replicates severe heat transfer deterioration (HTD) and buoyancy-induced improvements in heat transfer, showing robust predictive capabilities with a wide array of experimental data from both the authors and other researchers. The model was tested across ranges of P = 24.5–26.5 MPa, q/G = 0.11–0.67, and tube diameters of 7.5 mm, 26 mm and 43 mm. Additionally, the model's performance was benchmarked against experimental results of axially non-uniform heat flux conducted by the authors, successfully reproducing the variations in wall temperature due to changes in heat flux. This study substantially enhances the accuracy of numerical simulations for supercritical water in horizontal tubes, offering valuable insights for the engineering applications of supercritical water and the design of heat exchangers.