The Mechanism and the Magnitude of Flow Boiling Augmentation in Tubes with Discrete Surface Roughness Elements (III)

摘要

Related to other research on the effectiveness of flow boiling heat transfer augmentation using various types of turbulators this investigation comprises a definitive study of the effect of large discrete roughness elements on heat transfer over the entire range of forced convection operation -- from single-phase to critical heat flux. It was found that such elements provide significant augmentation (5-6 times smooth tube levels at equal Reynolds number) in the single-phase and partial boiling modes. However, the augmentation rapidly degrades as the developed boiling mode is entered. Critical heat flux was, in fact, lowered by 15 - 30 percent with the use of the large roughness elements. (Author Modified Abstract)