Nucleate pool boiling hear transfer of binary mixtures under microgravity

Abstract

Three heat transfer mechanisms associated with nucleate pool boiling of binary mixtures in low-flux regimes under microgravity are discussed. The examined mechanims are: (1) latent heat, (2) Marangoni flow, and (3) micro-convection. Using scaling analysis, the Marangoni flow heat transfer wass studied. The scaling laws derived for the Marangoni number and Nusselt number are supported by data reported previously in. the literature. The analysis and comparisons demonstrate that nucleate pool boiling heat transfer of binary mixtures under microgravity can be calculated by modifying constants found in a previous correlation by Sharp [1]. In highflux regimes, an analytical model for pool boiling heat transfer in binary mixtures is proposed. It is hypothesized that the interface is subjected to Helmholtz instabilities. Similar to terrestrial conditions, the nucleate pool boiling for binary mixtures at high heat fluxes in microgravity environments is also characterized by the existence of a liquid layer, known as the macrolayer, between the heater surface and the vapor mass. Compared with terrestrial conditions, the dual bubble layer structure can be maintain up to critical heat flux conditions. The .fraction of bubble contact area on the heater surface and the mitiat macrolayer thickness are derived in terms of thermophysical properties and/or heat flux. The predicted values compare well with exDerimenial data and the theoretical analysis. A critical heat flux model based on hydrodynamics is also introduced.