Countercurrent flow limitation in thin rectangular channels
Abstract
The phenomenon of countercurrent flow limitation (CCFL) in thin rectangular channels is important in determining the heat removal capability of research reactors which use platetype fuel elements similar to the MTR design. An analytical expression for predicting CCFL in narrow rectangular channels was derived from the momentum equations for the liquid and gas phase. The model assumes that the liquid downflow is in the form of a film along the narrower side walls of the channel, while the gas flow occupies the wide span of the rectangular channel. The average thickness of liquid film is related to the rate of gas flow through a stability criterion for the liquid film. The CCFL correlation agrees with air/water data taken at relatively high gas velocities. Depending on the magnitude of the dimensionless channel width, the new CCFL correlation approaches zero liquid penetration either in the form of a Wallis correlation or in terms of a Kutateladze number. The new correlation indicates that for a thin rectangular channel, the constant C in the Wallis flooding correlation depends on the aspect ratio of the channel. The approach to the appropriate asymptotic solutions also justifies the use of twice the wide span as the correct length scale for thin rectangular channels.
 Publication:

Presented at the American Nuclear Society Topical Meeting on Safety of NonCommercial Nuclear Reactor Research and Irradiation Facilities
 Pub Date:
 1990
 Bibcode:
 1990ans..meet.....C
 Keywords:

 Channel Flow;
 Counterflow;
 Gas Flow;
 Heat Transfer;
 Nuclear Reactors;
 Statistical Analysis;
 Forecasting;
 Interface Stability;
 Mathematical Models;
 Reactor Safety;
 Velocity;
 Fluid Mechanics and Heat Transfer