Analytical Modeling of Complete Nukiyama Curves Corresponding to Expected Low Void Fraction at High Subcooling and Flow Rate

Abstract

On the basis of a new hypothesis of thermodynamic states (the superheated wall layer is not metastable but saturated at locally elevated pressure), an analytical estimation is presented of the whole boiling curve [except critical heat flux (CHF), but fixed at this point, known by experiments or correlation]. The curvature of the boiling curve (bubbly flow) is deduced from thermodynamics of irreversible processes. The wall temperature corresponding to departure from nucleate boiling is calculated from balances of momentum at the interfaces, based on the assumption that the speed of sound may be a limit for maximum evaporation mass flux and thereby heat flux, i.e., CHF Heat flux during transition boiling is determined from balance of energy at the rewetting front. At the Leidenfrost point, a minimum heat flux is neglected. Thus, Leidenfrost temperature, as well as wall temperature at CHF, can be calculated analytically without using empirical coefficients. Heat flux of bubbly flow and transition boiling can be matched at any empirical CHF point. All these results are determined from properties of state alone, i.e., the models can be verified for all fluids including water and liquid metals (so far at moderate heat fluxes). Especially the latter two fluids are of interest for high-heat-flux application, and the precondition of low void fraction is expected to be fulfilled.