Boiling onset of nucleate

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)... 

Qi, S.L., Zhang, P., Wang, R.Z. and Xu, L.X., Flow Boiling of Liquid Nitrogen in Micro-Tubes Part I - The Onset of Nucleate Boiling, Two-Phase Flow Instability and Two-Phase Pressure Drop, Int J. Heat Mass Transfer, 50, 4999-5016, (2007). 

The onset of nucleate boiling (line XX in Fig. 15.88) occurs above the x = 0 line at low heat flux (i.e., there is a net bulk superheat of the liquid) but at qualities less than 0 for high heat fluxes, corresponding to the region of subcooled nucleate boiling. For heat transfer to a single-phase liquid, the wall superheat (ATsat)w can be calculated from... 

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