ABSTRACT

This paper mainly reviews research conducted by the authors on nucleate boiling, critical heat flux and transition boiling. Nucleate boiling curves are strongly influenced by the characteristics of the boiling surfaces, however it is quite difficult to establish a direct relation between the heat flux and the superheat taking account of surface characteristics. The paper discusses a method for predicting nucleate boiling curves with two correlations : one correlation relating the heat flux, the superheat, and the nucleation site density, and the other relating the nucleation site density and the  cavity density. By combining the two correlations, one correlation incorporating the effects of the surface characteristics can be derived. Critical heat flux (CHF) is achieved when a liquid macrolayer dries out just before departure of a vapor mass. The paper discusses the mechanism of the macrolayer formation, and proposes a model for the macrolayer formation based on considerations of boiling behavior under higher pressures. A dimensional analysis of the model leads to a semi-empirical correlation for the macrolayer thickness at CHF. One formulation of the model gives the well-known Kutateladze and Zuber corerelations for CHF, which was originally derived from physically unsustainable assumptions of the hydrodynamic instability. The macrolayer dryout model is also valid for transition boiling heat transfer. The paper shows that the macrolayer thickness in transition boiling agrees well with the correlation derived at the CHF, when assuming that there is no inflow of bulk liquid onto the heating surface before detachment of a vapor mass and that the heat flux at the macrolayer formation is given on the nucleate boiling curve extrapolated to the surface superheat of the transition boiling.