Author(s)

V. Chatoorgoon

Abstract

An experimental study was undertaken to rationalize data obtained from previous experiments where the bundle was heated electrically until CHF occurred, destroying ultimately the test bundle. (We term this ‘burnout’ from here on). The bundle exit temperature was always subcooled; hence, the channels contained only subcooled void preceding ‘burnout’. This study was undertaken to perform controlled experiments leading up to, but not including, the burnout power. Just prior to ‘burnout’ microscopic flow oscillations were exhibited between sub-channels. This was an interesting finding, as while the burnout power (especially for these bundles under sub-cooled boiling conditions) cannot be determined consistently with good accuracy through analytical methods, numerical methods for predicting the onset of flow oscillations are more accurate and well established. A stability analysis of the sub-channels of the single bundle, albeit without communication between the channels, was performed. Surprisingly, the predicted power at the onset of flow oscillations followed closely the experimental burnout power (of course, the latter was always slightly greater than the former, as would be expected). Keywords: CHF, flow instability, subcooled boiling, fuel bundle, low pressure. 1 Introduction Two-phase flow instabilities have been well researched, both experimentally and analytically. The analytical methods used for predicting them are also well established and have been abundantly benchmarked. However, in most reported experimental or analytical studies, the system considered was in a state of bulk boiling preceded by some small region of sub-cooled boiling. In all reported

Keywords

CHF, flow instability, subcooled boiling, fuel bundle, low pressure