Microchannel boiling

Fig. 2.33a-c Boiling in the central part of microchannels. Tls = 0.14 m/s, q = 220 kW/m. 1 Clusters of liquid droplets at the bottom of the channel. 2 Clusters of the liquid droplets on the side-wall. 5 Steam. Reprinted from Hetsroni et al. (2003b) with permission... 

Sobhan CB, Garimella SV (2001) A comparative analysis of studies on heat transfer and fluid flow in micro-channels. Microscale Thermophys Eng 5 293-311 Steinke M, Kandlikar SG (2003) Flow boiling and pressure drop in parallel flow micro-channels. In Kandlikar SG (ed) Proceedings of 1st International Conference on Micro-channels and Mini-channels, Rochester, 24-25 April 2003, pp 567-579 Thome JR (2006) State-of-the-art overview of boiling and two-phase flows in microchannels. Heat Transfer Eng 27(9) 4-19... 

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. 

Ghiaasiaan SM, Chedester RC (2002) Boiling incipience in microchannels. Int J Heat Mass Transfer 45 4599-4606... 

KandUkar SG (2002) Fundamental issues related to flow boiling in mini-channels and microchannels. Exp Thermal Fluid Sci 26 389-407... 

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... 

Wu HY, Cheng P (2003a) Liquid/two-phase/vapor alternating flow during boiling in microchannels at high heat flux. Int Comm Heat Transfer 39 295-302... 

Peng, C. F., Wang, B. X., Forced convection and flow boiling heat transfer for liquid flowing through microchannels, Int. J. Heat Mass Transfer 36 (1993) 3421-3427. 

For an extended review of experimental work on mini and microchannels, the reader is refered to the Thome (2004) and Kandlikar (2002) papers. This brief review covers a representative selection of heat transfer studies in minichannels and its aim is to illustrate the tendencies observed in the presented data. Recently Kandlikar (2004) developed a new general correlation adapted to minichannels which gives very good results for low qualities but fails to take dry-out into account, as noted by the author in question. Lately Thome et al. (2004) and Dupont et al. (2004) proposed a semi-empirical three zone model which is the only published work to predict the unique trends observed in minichannels. In this model the dominant boiling mechanism is the evaporation of the liquid film pressed under confined bubbles. 

S. Kandlikar. An extension of the flow boiling correlation to transition, laminar, and deep laminar flows in minichannels and microchannels . Heat Transfer Engineering, 25, 3, pp. 86-93 (2004). 

J. Thome. Boiling in microchannels a review of experiment and theory . International Journal of Heat and Fluid How, 25, pp. 128-139 (2004). 

Kandlikar, S.G., (2001), Two-phase flow patterns, pressure drop and heat transfer during boiling in minichannels and microchannels flow passages of compact evaporators. Keynote Lecture presented at the Engineering foundation Conference on Compact Heat Exchangers, Davos, Switzerland, July 1-6. 

Kuznetsov, V.V., Dimov, S.V., Shamirzaev, A.S., Houghton, P.A., Sunder, S., (2003), Upflow Boiling and Condensation in rectangular Minichannels, First International Conference on Microchannels and Minichannels, April 24-25, Rochester, New York Editor S.G. Kandlikar, pp.683-689. 

The nature of boiling heat transfer in a channel with the gap less than the capillary is also studied and presented. The condensation flow mechanisms, pressure drop and heat transfer in microchannels, role of microscale heat transfer in augmentation of nucleate boiling and flow boiling heat transfer, binary-fluid heat and mass transfers in microchannel geometries for miniaturized thermally activated absorption heat pumps, evaporation heat... 

Heat transfer can also be enhanced by application of an electric field. In boiling heat transfer, electric fields have been successfully used to control nucleation rates and achieve a continuous rise in heat transfer coefficient. Up to a sevenfold heat transfer enhancement by the electric field in falling film evaporators has been reported. In the presence of an electric field, both AC and DC, the mixing length in microchannels is shortened considerably, by a factor 30 or more. 

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