CFD implementation and experimental validation of the Chen model for heat transfer in nucleate boiling

摘要

The present paper describes a nucleate boiling model based on Chen's correlation, and posterior validation with experimental data. When using a heat exchanger with a liquid coolant, if the wall exceeds the saturation temperature of the liquid at system's pressure, it may boil, increasing the heat transfer law. The aim of this study is to validate the model developed with some experiments carried out in a heated flat probe. The proposed algorithm consists of a heat flux partition in two terms, one regarding the forced convection heat transfer existing in the free-boil area, and the other term considers the heat transfer increment due to the nucleate boiling. Consequently, general results show lower temperatures in the wall because of the increased heat flux, proved in several industrial components within these conditions. To achieve the model validation, some simulations were developed with the CFD software Ansys Fluent, configured with the same geometry and conditions as our experimental installation. Using a copper conduction, a heat flux up to 2MW is used to increase the temperature of a wall in contact with water, which flows through a 20mm wide and 25mm high duct. Heat transfer data are recorded while the temperature increases, allowing us to compare the boiling curves with the CFD boiling model results. Data comparisons show a good agreement with five cases studied at different conditions of system pressure and velocity and temperature inlet. An implementation of a widely used boiling model has been developed and its results have been validated with our experimental data, providing a good agreement under the specified conditions. The obtained results have shown an important improvement with respect to other multiphasic and standard models, offering better results simulating industrial components.