Numerical and experimental investigation of convective flow boiling in vertical annulus using CFD code: Effect of mass flow rate and wall heat fluxes

Abstract

In this paper a numerical and experimental analysis of convective flow boiling in a vertical annular channel has been performed. As the best substitute for water, a refrigerant Trichlorofluoromethane CCl3F (R11) has been selected for the working fluid in the experiment to evaluate the capability of the Computational Fluid Dynamic (CFD) codes to predict the heat transfer rates, transitions points and the boiling flow regime. The experiments cover a wide range of mass fluxes (435–1443 kg/m2 s) and heat fluxes (1.81–11.5 W/cm2), which enabled to study the influence of different boundary conditions on the development of local boiling phenomena up to CHF occurrence. The contribution of each of the mechanisms for transfer of heat to the liquid – forced convection and quenching, as well as the energy transport associated with vapor generation has been quantified in terms of nucleation site densities, bubble departure, bubble detachment frequency, flow parameters like velocity, inlet subcooling and wall superheat. The qualitative and quantitative trends of the parameters studied experimentally are also supported by the analysis and observation of the various phenomena visualized. A sensitivity analysis of several modeling parameters on the radial distribution of flow quantities has highlighted the importance of correct description of the boiling model. Also, some measurements have been compared to the predictions by the three-dimensional two-fluid model of subcooled boiling flow carried out with the computer code. The computational method has been tested against experimental data. The comparison shows a good agreement between the predicted and experimental results.