Models for enhanced boiling heat transfer by unusual, Marangoni effects under microgravity conditions

A new approach is suggested to enhance boiling heat transfer through introd uction of unusual surface tension effects. The surface tension of aqueous s olutions of alcohols with a chain length longer than four carbon atoms offe rs a positive gradient with temperature when the temperature exceeds a cert ain value. Moreover, the positive gradient near the boiling point has avery large value. This will generate a considerable driving force for bubble de parture. As a result, in the nucleate boiling of these solutions, the Maran goni effect around the bubble surface will not impede the bubble detachment from the heater surface but rather will provide an additional driving forc e for the bubble departure. This effect combines with the buoyancy under no rmal gravity and acts as a main driving force of bubble departure in microg ravity. Models for predictions of the bubble detachment diameters, the nucl eate boiling heat transfer coefficient, and the critical heat flux are deve loped. (C) 1999 Elsevier Science Ltd.