Nucleation reduced rate

Cathodic protection is sometimes beneficial to avoid cavitation, not because of the reduced rate of corrosion but because of the cushioning effect of hydrogen evolved on the surface. Removal of dissolved air is often beneficial because dissolved gases more easily nucleate cavitating bubbles at low pressures. 

The extensive series of studies on in vitro core formation reported by Harrison and co-workers (32, 63, 82, 140) and others (133) has led to the development of a three-step hypothesis for iron uptake. In the first step, iron entry through the channels, Fe + passes from the outside of the protein through the channels in the apoferritin coat to the interior cavity. The second step, nucleation, involves iron binding to groups on the inner surface of the protein in such a way that a small cluster of coupled Fe ions is formed. The final step, formation of the core, involves the extension of a small nucleating cluster by the addition and oxidation of Fe +. This stage is characterized by an initial catalytic phase, during which the small cluster rapidly expands, followed by a reduced rate of expansion once the core has attained a particular size (—1000-1500 iron atoms per molecule). 

However, in the case of mini- and microemulsions, processing methods reduce the size of the monomer droplets close to the size of the micelle, leading to significant particle nucleation in the monomer droplets (17). Intense agitation, cosurfactant, and dilution are used to reduce monomer droplet size. Additives like cetyl alcohol are used to retard the diffusion of monomer from the droplets to the micelles, in order to further promote monomer droplet nucleation (18). The benefits of miniemulsions include faster reaction rates (19), improved shear stabiHty, and the control of particle size distributions to produce high soHds latices (20). 

In a study where the uniform nucleation rate was varied over several values at a fixed strain rate of = 10 /s, the fragment number results shown in Fig. 8.21 were obtained. At lower nucleation rates nearly all fracture initiation sites grow to completion and provide the reduced number of fragments shown. 

The uniformity of film thickness is dependent upon temperature and pressure. The nucleation rate rises with pressure, such that at pressures above atmospheric the high rate of nucleation can lead to comparatively uniform oxide films, while increase in temperature reduces the density of oxide nuclei, and results in non-uniformity. Subsequently, lateral growth of nuclei over the surface is faster than the rate of thickening until uniform coverage is attained, when the consolidated film grows as a continuous layer ... 

The conclusion to be drawn from the above examples and many others is that softness in a boiling system, preceding the boiling channel inlet, may cause flow oscillations of low frequency. It is probably the pressure perturbations arising from the explosive nature of nucleate boiling that initiates the oscillation, and the reduced burn-out flux which follows probably corresponds to the trough of the flow oscillation, as a reduction in flow rate always drops the burn-out flux in forced-convection boiling. 

---