Prediction of the local pressure gradient during partially developed subcooled boiling in research reactors of high power density

A model is presented for predicting the pressure gradient in partially developed subcooled boiling of water for velocities from 15 to 30 m/s and inlet peaked, nonuniform axial flux profiles with channel average flux values of 6 MW/m². The partially and fully developed boiling regions are considered separately, however; the same general modeling technique is used for both. Several correlations for the void fraction at onset of significant void are considered, and their effect on the channel pressure drop is evaluated. The effect of nonuniform axial heat flux on the channel pressure drop is also evaluated. The model is compared with pressure drop data from the thermal-hydraulic test loop at Oak Ridge National Laboratory and is found to agree with the data within 24%.