Modeling of subcooled boiling by extending the RPI wall boiling model to ultra-high pressure conditions

Accurate predictions of the two-phase flow pattern and heat transfer inside the high-pressure tubes is of great importance for the safety of steam power equipment. In this paper, subcooled boiling flow was numerically modeled and the RPI (Rensselaer Polytechnic Institute) wall boiling model was extended to ultra-high pressure conditions up to 15 MPa. Various combinations of closure models for the key parameters in RPI model, including the nucleation site density (Nw), bubble departure diameter (Dw) and bubble departure frequency (f), were studied in the pressure range of 3-15 MPa. The numerical results were carefully validated by comparing the simulations with the experiments of Bartolemei et al. (1967, 1982). A widely applicable combination of closure models for Nw, Dw and f was identified for the pressure range from low to ultra-high levels, with the mass flux range of 503-2123 kg/(m2 s) and the heat flux range of 0.42-2.21 MW/m2. The characteristic parameters of wall subcooled boiling were analyzed and the physical process of subcooled boiling was revealed. Based on the optimized models, the influence of operating parameters including mass flux and heat flux was also studied under the pressures of ∼11 MPa and ∼15 MPa.