The flow models for critical heat flux in flow boiling in tubes and rod bundle geometries are reviewed. Sadeghlou's C6D correlation for vertical 37-element bundles at 1000 psia is reviewed and the significance of the Becker-type quality correction factors for geometry/ pressure/ radial flux depression/ heat flux and bundle junction end plates are examined. A CHF correlation for vertical 37-element bundles is presented which describes the available high mass flux data with an rms error of 4.3%.
The effect of buoyant forces on CHF in horizontal flow tubes is reviewed. A brief review of the principles of similitude and modeling along with a description of their application to Freon-to-water modeling in CHF experiments is given. Ahmad's  method of compensated distortion is described and his scaling flow parameter fervertical orientations presented. Meri lo' s  development of adimensionless scaling flow parameter for horizontal tubes is described. Using the techniques of Ahmad and Merilo, and CHF data from 37-element bundles cooled by Freon and by water, a scalin9 flow parameter for horizontal conditions in 37-element bundles is developed. Using this scaling flow parameter, the calculation of water-equivalent results from Freon-12 CHF data is described. A CHF correlation for horizontal 37-element CANDU bundles is present~d, which describes the water-equivalent data and the actual water data in the range of interest with a rms error of 4.4%. The application of this CHF correlation to the design of CANDU fuel channels is discussed and the benefits of the use of this correlation over the current approach are stated.