New correlation for Critical heat flux in annuli with low pressure water at low flow rates

Abstract

Calculation of CHF (Critical Heat Flux) for low pressure low flow water in annuli is required in the design and analyses of conventional nuclear reactors as well as the newer advanced nuclear reactors. Correlations for high pressure high flow have been found to fail for low pressure low flow conditions. There are no well-verified correlations under these conditions. The few published correlations have been verified with only a limited amount of data. In the present research, these correlations were compared to all available data which was from many sources. None of them was found satisfactory. A new correlation was therefore developed which agrees well with all available data for vertical annuli with upflow. The range of data included annular gaps 0.9 to 16.5 mm, pressures 1 to 3.2 bar, mass flux 1 to 1030 kg/m²s, and inlet quality −0.17 to 0. The new correlation had MAD (mean absolute deviation) of 19.6 % with 273 data points from 13 sources. The MAD of other correlations ranged from 45.3 % to 99.7 %. In this paper, previous work is reviewed, development of the new correlation is described, and comparison of the new and earlier correlations with test data is presented. Recommendations are made for its application.