On boiling incipience due to contact angle hysteresis

The incipience of boiling on a metal surface is largely due to instability of the vapour-liquid interfaces which exist in minute natural cavities. The influences of surface roughness and contact angle on the equilibrium of the interface are studied and expressions relating roughness and advancing and retarding contact angles to the possibility of vapour trapping are developed. A model of boiling incipience based on contact angle hysteresis between the advancing and retarding angles of the interface within the cavity is presented. This hysteresis arises naturally from the roughness and heterogeneity of a surface on the microscopic scale and thus occurs on normal engineering boiling surfaces. The model predicts incipience at smaller radii than the cavity mouth radii and successfully explains the observed features of boiling incipience without postulating the existence of re-entrant cavities. © 1982.