Boiling in Micro-Channels

L.P. Yarin, Fluid Flow, Heat Transfer and Boiling in Micro-Channels Springer 2009... 

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. 

As boiling in micro-channel heat sinks is an attractive method for cooling computer CPUs and other high-heat flux devices (such as laser diodes), it is of crucial importance to accurately predict the critical heat flux (CHF) in the small-diameter channels. Critical heat flux or burnout is a limiting value for safe operation of heat dis-... 

The subject of Chap. 6 is boiling in micro-channels. Several aspects of boiling are also considered for conventional size channels and comparison with micro-channels was carried out. Significant differences of ONB in micro-channels have been discussed compared to conventional channels. Effect of dissolved gases on boiling in water and surfactant solution was revealed. Attention was paid on pressure drop and heat transfer, critical heat flux and instabilities during flow boiling in microchannels. 

Visual observation in the studies by Hetsroni et al. (2002a,b, 2003), Qu and Mudawar (2002) proved bubble behavior at incipient boiling in micro-channels (d i < 1 mm) and concluded that it was quite different from that in larger channels. After nucleation, bubbles first grew to detachment size before departing into the liquid flow. The detachment size was comparable to that of the micro-channel... 

The influence of inlet conditions on stability of flow boiling in micro-channels was analyzed by Brutin and Tadrist (2004). The set-up with rectangular micro-channel 500 X 4,000 jm was used to study flow boiling at two kinds of upstream conditions, which corresponded to constant liquid velocity at channel entrance (confinement condition) and constant velocity at the syringe outlet. The flow characteristics corresponding to steady and unsteady regimes were studied and the Reynolds number that subdivided these states was found. 

The convective and nucleate boiling heat transfer coefficient was the subject of experiments by Grohmann (2005). The measurements were performed in microtubes of 250 and 500 pm in diameter. The nucleate boiling metastable flow regimes were observed. Heat transfer characteristics at the nucleate and convective boiling in micro-channels with different cross-sections were studied by Yen et al. (2006). Two types of micro-channels were tested a circular micro-tube with a 210 pm diameter, and a square micro-channel with a 214 pm hydraulic diameter. The heat transfer coefficient was higher for the square micro-channel because the corners acted as effective nucleation sites. 

Table 6.8 Two-phase flow boiling in micro-channels. Heat transfer coefficient. Reprinted from Lee and Mudawar (2005b) with permission...

The work by Steinke and Kandlikar (2004b) focused on the obtaining heat transfer data during flow boiling in micro-channels. An experimental investigation was performed for flow boiling using water in six parallel, horizontal micro-channels... 

Kandlikar SG (2006) Nucleation characteristics and stability considerations during flow boiling in micro-channels. Exp. Thermal and Fluid Science 30 441 47 Katto Y, Ohno H (1984) An improved version of the generalized correlation of critical heat flux for the forced convective boiling in uniformly heated vertical tubes. Int J Heat Mass Transfer 27 1641-1648... 

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