Supercritical Water In Vertical Tubes Research Articles

Numerical Investigation on Heat Transfer of Supercritical Water With a Variable Turbulent Prandtl Number Model

Abstract Turbulent Prandtl number (Prt) has a great impact on the performance of turbulence models in predicting heat transfer of supercritical fluids. Unrealistic treatment of Prt may lead to large deviations of the prediction results from experimental data under supercritical conditions. In this study, the effect of Prt on heat transfer of supercritical water was extensively studied by using shear stress transport (SST) k–ω turbulence model, and the results suggested that using the existing Prt models would lead to failures in predicting the heat transfer characteristics of supercritical water under deteriorated heat transfer (dht) conditions. A new variable Prt model was proposed with the Prt varied with pressure, turbulent viscosity ratio, and molecular Prandtl number. The new model was validated by comparing the numerical results with the corresponding experimental data, and it was found that the new variable Prt model exhibited better performance on reproducing the dht of supercritical water in vertical tubes than those of the existing Prt models.

Numerical Investigation of Heat Transfer to Supercritical Water in Vertical Tube under Semicircular Heating Condition

In-depth understanding and analysis of turbulent convection heat transfer of supercritical water under semicircular heating conditions play a major role in system design and security. The inaccurate numerical results on simulating the buoyancy effect under deterioration heat transfer cases are partly attributed to the invalidity of the turbulent model. An improved turbulence model, which is validated suitable to three-dimensional model, is adopted in the present paper to numerical simulated flow and heat transfer in a vertical tube under semicircular heating condition. Heat transfer deterioration phenomenon occurs under semicircular heating condition, while the degree of deterioration is weakened due to the influence of variable physical properties and buoyancy effect. The velocity profile is distorted into “M-shape” in the heating side and present parabolic distribution in the adiabatic side, leading to different deterioration mechanisms under semicircular heating condition compared with uniform heating. The larger density difference between the heating side and the adiabatic side increases the shear stress production of turbulent kinetic energy; turbulent development is much faster recovery than the phenomenon in uniform heating condition. The results show that the semicircular heating condition can effectively alleviate the degree of heat transfer deterioration in a vertical tube.

Corrigendum to “Development of a new empirical correlation for the prediction of the onset of the deterioration of heat transfer to supercritical water in vertical tubes” [Int. J. Heat Mass Transfer 102C (2016) 133–141

Corrigendum to “Development of a new empirical correlation for the prediction of the onset of the deterioration of heat transfer to supercritical water in vertical tubes” [Int. J. Heat Mass Transfer 102C (2016) 133–141

Erratum to “Development of a new empirical correlation for the prediction of the onset of the deterioration of heat transfer to supercritical water in vertical tubes” [Int. J. Heat Mass Transfer 102 (2016) 133–141

Erratum to “Development of a new empirical correlation for the prediction of the onset of the deterioration of heat transfer to supercritical water in vertical tubes” [Int. J. Heat Mass Transfer 102 (2016) 133–141

Development of a new empirical correlation for the prediction of the onset of the deterioration of heat transfer to supercritical water in vertical tubes

Heat transfer to supercritical water is relevant for modern power applications such as supercritical water reactors, supercritical boilers in fossil-fired power plants or future concepts for supercritical solar-thermal power plants. The phenomenon of deteriorated heat transfer (DHT), caused by the strong variation of fluid properties at pressures above the critical pressure is still not thoroughly understood to date. At the same time it is of great importance for plant design and operation. Disagreements exist regarding its definition, its prediction and the mechanisms leading to its occurrence. This study evaluates the performance of empirical correlations for the a-priori prediction of the heat flux causing the onset of DHT in heated vertical tubes with an internal upward flow of supercritical water and proposes a new correlation. Also, definitions from literature are discussed, and the most frequently used quantitative definition: α<0.3·αNHT is selected for correlation analysis and development. It is emphasized that the predictive capability of a correlation for the deterioration of heat transfer is limited when no definition for this phenomenon is provided. For the evaluation of the existing correlations and the development of the new correlation, heat transfer data consisting of 4455 data points from 14 independent references is considered. This data set is reduced to 32 independent experiments reflecting the heat flux causing the onset of DHT. The newly developed correlation has a mean average relative deviation of 12.9% and predicts 78.1% of the DHT data within ±20%. This is a significant improvement compared to the best existing correlation with a mean average relative deviation of 23.4% and which predicts 56.3% of the DHT data within ±20%.

A numerical study of heat transfer to supercritical water flowing upward in vertical tubes under normal and deteriorated conditions

A numerical study of heat transfer to supercritical water in vertical tubes is carried out using the ANSYS-CFX code and employing the k–ω SST turbulence model. The numerical results on wall temperature distributions under normal and deteriorated heat transfer conditions are compared with experimental data and a good agreement is obtained. The onset of deterioration is captured for both low-flow and high-flow conditions. Sensitivity of numerical results to operational conditions and the turbulent Prandtl number (Prt) is investigated. The grid independent solution is obtained when y+ is less than 1 and the cell aspect ratio is less than 2000. It is concluded that the turbulent Prandtl number has a quite significant influence on the calculated wall temperature and the best agreement with experimental data is obtained when Prt is close to 0.9.

Experimental and numerical investigation of turbulent convective heat transfer deterioration of supercritical water in vertical tube

Abstract The heat transfer phenomenon at supercritical pressure is different from the normal pressure due to the strong variation of thermal physical properties near the pseudo-critical point. The strong change of density leads to a great buoyancy effect at low flow rate, and flow acceleration at high flow rate, both of which influence heat transfer characteristics significantly. In this paper an experimental study is performed to analysis the heat transfer behavior of supercritical water. The test section is a vertically 10-mm ID tube with uniformly heating. Heat transfer deterioration phenomenon caused by the buoyancy effect and the acceleration effect is identified. At the same time, the heat transfer character of upward and downward flow is numerical studied by an in-house CFD– code developed by Shanghai Jiao Tong University. An improved k – ɛ – k t – ɛ t model is proposed and installed in this code. The wall temperature, especially near the heat transfer deterioration, is well predicted by this new model, compared with the traditional turbulence models. It is shown that the buoyancy effect causes shear stress and radial flow velocity redistribution which leads to heat transfer deterioration and recovery. Moreover, buoyancy can influence the turbulent kinetic energy dramatically, which will affect heat transfer capacity. In the downward flow case with high flow rate, the effect of buoyancy on heat transfer is not so obvious. However, as found in numerical study, the heat transfer deterioration caused by flow acceleration can occur both in upward and downward flow.