NUCLEATE BOILING OF BINARY MIXTURE AT HIGH HEAT FLUX UNDER MICROGRAVITY

An analytical model for nucleate pool boiling heat transfer of binary mixtures in high-flux regime is formulated according to Helmholtz instability theory of vapor-liquid interface.The nucleate pool boiling for binary mixtures at high heat flux under microgravity is also characterized by the existence of a liquid layer known as macrolayer between the heater surface and the vapor mass.The dual bubble layer structure can maintain up to CHF condition due to less buoyancy.The expressions for fraction of bubble contact area on the heater surface and initial macrolayer thickness are derived in term of the thermophysical properties or/and the heat flux.A CHF model based on hydrodynamics is provided.The predicted results are compared with experimental data and theoretical analysis.Some important conclusions are drawn as follows:The fraction of bubble contact area on the heater surface is independent of the input heat flux,but much greater than that at terrestrial conditions;Initial macrolayer thickness is much greater than that at terrestrial conditions due to less velocities of vapor phase and liquid phase;The CHF values for binary mixtures under microgravity are about 60～80% of those at terrestrial conditions,but are much greater than those of single components under microgravity.