Active nucleation site density in boiling systems

Abstract

Realizing the significance of the active nucleation site density as an important parameter for predicting the interfacial area concentration in a two-fluid model formulation, the active nucleation site density has been modeled mechanistically by knowledge of the size and cone angle distributions of cavities that are actually present on the surface. The newly developed model has been validated by various active nucleation site density data taken in pool boiling and convective flow boiling systems. The newly developed model clearly shows that the active nucleation site density is a function of the critical cavity size and the contact angle, and the model can explain the dependence of the active nucleation site density on the wall superheat reported by various investigators. The newly developed model can give fairly good predictions over rather wide range of the flow conditions (0 kg/m 2 s ⩽ mass velocity ⩽ 886 kg/m 2 s; 0.101 MPa ⩽ pressure ⩽ 19.8 MPa; 5° ⩽ contact angle ⩽ 90°; 1.00×10 4 sites/m 2 ⩽ active nucleation site density ⩽ 1.51×10 10 sites/m 2).