EFFECTS OF GRAVITY ON THE BOILING OF BINARY-FLUID MIXTURES

Experiments have been conducted with water/2-propanol mixtures under r educed gravity, normal gravity and high gravity in order to investigat e Marangoni effects and their interaction with the gravitational effec t in the pool boiling of binary mixtures. The system pressure was suba tmospheric (similar to 8 kPa at 1 g(n)) and the bulk liquid temperatur e varied from low subcooling to near saturation. The molar concentrati ons of 2-propanol tested were 0.015, 0.025 and O.1. The reduced and hi gh gravity experiments were conducted aboard a DC-9 aircraft at NASA L ewis Research Center. Boiling curves were obtained both for high gravi ty (similar to 2 g(n)) and reduced gravity (similar to 0.01g(n)) and t he duration of both the:high gravity and reduced gravity period was ap proximately 20 s per parabola. For each concentration of 2-propanol, t he critical heat flux (CHF) has been determined for normal and reduced gravity conditions. The present experimental data are compared with t he available predictive correlations for binary mixture boiling heat t ransfer and critical heat flux conditions. Comparison of boiling curve s obtained from the experiment under 2-g(n), 1-g(n) and reduced gravit y indicates that the boiling mechanism in-these mixtures is nearly ind ependent of gravity. The CHF values determined under reduced gravity c onditions for each concentration did not change significantly from tho se measured under 1-g(n) conditions. The results also indicate that th e Marangoni mechanism is strong enough in these mixtures to sustain st able nucleate boiling under reduced gravity conditions. (C) 1998 Elsev ier Science Ltd; All rights reserved.