EVOLUTION OF VAPOR BUBBLES IN BOILING

A new dynamic theory is proposed of the growth and detachment of vapor bubbles forming on a superheated surface under conditions of nucleate boiling. The equations, describing the increase of the bubble volume and the motion of its center of gravity, are derived for a unified sch eme from the law of conservation of mechanical energy of a bubble-liqu id system. These equations are free of semiempirical assumptions chara cteristic of most investigations in the region under treatment. Invest igated by way of example is the evolution of a bubble on a horizontal wall, the growth of which is controlled by the rare of vaporization fr om the bulk of surrounding liquid and from the microlayer separating t he bubble from the wall. The new theory is free of the errors of previ ous studies and helps explain a whole series of effects which, until n ow, remained unclear. fn particular, it is demonstrated that the force due to the surface tension effects promotes, rather than impedes, bub ble detachment. Explanations are provided for the first time for the d ependence of the bubble departure size on thermal factors and for the dependence of the rate of its growth on dynamic factors. The conclusio ns are supported by the results of experiments in nucleate boiling und er conditions of reduced gravitation.