In the present study, we numerically simulated subcooled boiling flow in a circular-vertical flow channel using our one-dimensional DFM4 computer codes. We extended our existing DFM4-codes to (1) improve the convergence of the numerical methods, resulting in substantially reduced errors for the overall mass and energy, (2) calculate implicitly the wall temperature, and (3) incorporate the accurate closure relations for the bubble departure diameter dbw to be used at high and low pressures These improvements helped us compute more accurately dbw and the local void fraction α, which were very close to the experimental results and the computational fluid dynamics (CFD) results, compared to those calculated in our recent studies.

A major contribution of this work is to study numerically the bubble dynamics features at a high pressure, which a large number of studies in the literature. One interesting feature of our improved DFM4-CFD model is that the codes retain the nonequilibrium condition for a highly subcooled flow boiling, while our previous codes attained the equilibrium condition very fast at the identical conditions and computed significantly higher α, compared to the experiments. We have also seen that the Unal correlation for dbw is accurate enough at high and low pressures, and the Tolubinsky-Kostanchuk correlation for dbw is reasonable only at a high pressure.