Evaporative instability at the superheat limit

The explosive vaporization of a single bubble inside a droplet of butane heated to the limit of superheat has been investigated experimentally using short-exposure photographs and fast-response pressure measurements. An interfacial instability driven by rapid evaporation has been observed on the surface of the bubbles. It is proposed that the Landau mechanism of instability, originally described in connection with the instability of laminar flames, also applies to rapid evaporation at the superheat limit. Calculations suggest that other technically important fluids may be even more unstable when boiling at the superheat limit. The rate of evaporation after the onset of instability is estimated from the experimental measurements to be two orders of magnitude greater than would be predicted by conventional bubble-growth theories that do not account for the effects of instability. An estimate of the mean density within the bubbles during the evaporative stage indicates that it is nearly equal to the critical density of butane.