Suscripción a Biblioteca: Guest

ISSN Online: 2377-424X

ISBN Print: 0-89116-559-2

International Heat Transfer Conference 8
August, 17-22, 1986, San Francisco, USA

SUPERHEATING OF LIQUIDS AT THE ONSET OF BOILING

Get access (open in a dialog) DOI: 10.1615/IHTC8.3930
pages 2001-2006

Sinopsis

Boiling is a process of phase transition in the metastable state of a liquid. The onset of boiling can be explained by the process of nucleation or of nucleus activation. In the case of nucleation a nucleus is formed within the superheated liquid by thermal fluctuations of molecules. These fluctuations effect clusters of molecules with vapor like energies up to the critical size, the so-called nuclei. If the fluctuation process occurs in a homogeneous liquid it is known as homogeneous nucleation. The formation of nuclei in a liquid with contact to a solid surface is refered to as heterogeneous nucleation, provided that there is no vapor or gas trapped in cavities of the surface.
The activation process is based on the assumption of preexisting vapor nuclei trapped in surface cavities. Stability considerations at the vapor-liquid interface prove that trapped vapor can stable exist in cavities. Furthermore a criterion for the activation of potential sites is deduced. With this criterion and the knowledge of the preceeding process a prediction of superheat at onset of boiling is possible. From the comparison of these two different methods it must be assumed for technical surfaces that the onset of boiling starts from an activation process of preexisting nuclei.