A simple two-phase thermal-hydraulic tool with the drift-flux model has been used to develop a subcooled boiling model. The tool is composed of four governing equations: mixture mass, vapour mass, mixture momentum, and mixture enthalpy. The constitutive relations were implemented into the tool: relative velocity, interfacial mass transfer, wall heat transfer, and wall friction.
Using the developed tool, various subcooled boiling models were investigated through the published experimental data. In the process of evaluation, we developed two models associated with the subcooled boiling. First, the Saha and Zuber correlation predicting the point of the net vapour generation was modified to consider the thermal and dynamic effects at the high velocity region. Second, the pumping factor model was developed by pi-theorem based on parameters related to bubble generation mechanism: it produced an additional parameter, Boiling number.
The proposed models and several models were evaluated against a series of subcooled flow boiling experiments at the pressure range from 1 bar to 146.8 bar. From the root mean square analysis for the predicted void fraction in subcooled boiling region, the results of the proposed model at low pressures were comparable to the Zeitoun model which was the best at low pressures and were in best agreement with the experimental data at high pressures. The proposed model presented the best predictions for the whole pressure ranges. Also, the implementation of the developed models into RELAP5/MOD3.3 brought about the improved results compared to those of the default model of the code.