Onset of nucleation

Crystallization. Acidified aluminum sulfate solutions can be supercooled 10 °C or more below the saturation point. However, once nucleation begins, the crystallization rate is rapid and the supersaturated solution sets up. The onset of nucleation in a gentiy stirred supersaturated solution is marked by the appearance of silky, curling streamers of microscopic nuclei resulting from orientation effects of hydraulic currents on the thin, platelike crystals. Without agitation, nucleation in an acidified solution, in glass tubes, can yield extended crystalline membranes of such thinness to exhibit colors resulting from optical interference. 

The concepts of boiling in micro-channels and comparison to conventional size channels are considered in Chap. 6. The mechanism of the onset of nucleate boiling is treated. Specific problems such as explosive boiling in parallel micro-channels, drag reduction and heat transfer in surfactant solutions are also considered. 

Onset of Nucleate Boiling in Conventional Size Channels... 

Table 6.1 Onset of nucleate boiling. Characteristics of experiment...

Onset of Nucleate Boiling in Conventional Size Channels where / = 2Tw/(pt/ ), tw is the wall shear stress. 

Onset of Nucleate Boiling in Parallel Micro-Channels 6.2.1 Physical Model of the Explosive Boiling... 

The temperatures on the heater rw,0NB. and heat fluxes onb corresponding to onset of nucleate boiling in water and surfactant solution that contain dissolved gases are presented in Table 6.5. 

Table 6.5 Onset of nucleate boiling in fluids that contain dissolved gases. Reprinted from Klein et al. (2005) with permission...

For qualitative analysis of the conditions at which the boiling incipience was studied experimentally the parameter D = ATsub.oNB / s may be used. Depending on the value of D, the channels can be subdivided into two groups D < 1 and D < .. When D < D = 0.125—0.25) the onset of nucleate boiling occurred at a bulk temperature significantly less than saturation. When D nucleate boiling occurred at values of the bulk temperature close to saturation. 

Li HY, Tseng FC, Pan C (2004) Bubble dynamics in micro-channels. Part II two parallel microchannels. Int J Heat Mass Transfer 47 5591-5601 Li J, Cheng P (2004) Bubble cavitation in a micro-channel. Int J Heat Mass Transfer 47 2689-2698 Liu D, Lee PS, Gaiimella SV (2005) Prediction of the onset of nucleate boiling in microchannel flow. Int J Heat Mass Transfer 48 5134-5149... 

Bar-Cohen, A., 1992, Hysteresis Phenomena at the Onset of Nucleate Boiling, Engineering Foundation Conf. on Pool and External Flow Boiling, Santa Barbara, CA, pp. 1-14. (4)... 

The rate of bubble collapse Rcl is primarily important in the first transition zone where the bulk liquid is subcooled. A number of studies have been published on subcooled boiling as well as the prediction of the point of net vapor generation, characteristics defining Transition Zone I, and the onset of nucleation. These studies all result in empirical correlations, and have not led to quantitative conclusions which can be generalized. The radial velocity... 

FBRM provides a real time chord length distribution within the crystallizer. The technique is excellent for determining the onset of nucleation and in following general growth rate and rate transitions associated with polymorphic transformation, reaching equilibrium and attrition effects. 

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