Liquid breakdown, thermal mechanisms

Sharbaugh, 1960) proposed a thermal mechanism for the liquid breakdown which involves the formation of a bubble or a region of lower density. Under typical conditions of pulse breakdown of alkanes, a breakdown field strength of about 1.6 MV/cm is measured. An enhancement of the electric field strength at the tips of asperities of 5 is assumed. The local current density is of the order of 10 A cm". The specific local power input, Vf oc, is then given as... 

A solid or liquid dielectric inserted between two electrodes can support only a limited voltage. Several physical mechanisms can lead to a current instability and to breakdown, e.g., thermal instabilities in materials with thermally activated conductivities, transitions from trap-controlled transport to band transport, impact ionization, etc. (Zeller, 1987). Which one of the different mechanisms ultimately determines the dielectric strength depends on materials parameters, geometry, voltage pulse forms (including history), temperature, etc. (O Dwyer, 1973). 

The coalescence of liquid droplets, therefore, is intimately related to the nature of the thin lamellar film formed between them as they are brought into close encounters as a result of thermal convection. Brownian motion, or mechanical agitation. It is important to understand the nature of the forces acting across the film in order to obtain information about the thermodynamic stability, metastability, or instability of the film, and the kinetic processes that will control the rate of film breakdown. Comprehensive reviews of those aspects of emulsion stability can be... 

---