Condensation in Microchannels

Development of additional models for pressure drop in noncircular channels, and for heat transfer coefficients and transition criteria based on nondimensional parameters is underway. This integrated approach using flow visualization, pressure drop and heat transfer measurements, and analytical modeling, is yielding a comprehensive understanding of condensation in microchannels. 

This chapter focuses on single-phase flow heat transfer in microchannels. For heat transfer of boiling and condensation in microchannels, the interested reader is referred to reviews by Kandlikar [2] and Thome [3]. 

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. 

CONDENSATION FLOW MECHANISMS, PRESSURE DROP AND HEAT TRANSFER IN MICROCHANNELS... 

Garimella, S., and Bandhauer, T. M. (2001) Measurement of Condensation Heat Transfer Coefficients in MicroChannel Tubes, 2001ASME International Mechanical Engineering Congress and Exposition, New York, NY, United States, Vol. 369, American Society of Mechanical Engineers, pp. 243-249. 

Bandhauer, T. M. (2002) Heat Transfer in MicroChannel Geometries During Condensation cfRI34a, Master of Science Thesis, Mechanical Engineering, Iowa State University, Ames, lA, p. 201. 

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... 

Knoevenagel condensation in a microflow reactor using immobilized piperazine on silica has also been reported. The condensation is carried out in an 800 x 100 pm catalyst channel in borosUicate glass under the EOFconditions (SchemeS.15) [29,30]. Similar work with amine-functionalized silica coatings on microchannel walls has also been reported [31]. 

Figure 1 shows the experimental setup for the study of condensation in a microchannel [5], The deionized water in the water tank was pumped into the electric boiler where water was vaporized. Saturated steam from the boiler flowed successively through the valve, filter, and test section and was finally collected by a container at atmospheric pressure. Figure 2 shows the test section of the parallel microchanneis etched in a silicon wafer, which was cooled by circulation of cooling water from the bottom of the wafer. Temperature and pressure of steam at the inlet and the condensate at the outlet were measured by thermocouples and pressure transducers, respectively. WaU temperature distribution along the bottom of the microchaimels was measured by thermocouples embedded in the silicon wafer substrate. The microchanneis were then covered with thin transparent Pyrex glass from the top. To visualize condensation flow patterns... 

Condensation in Microchanneis, Figure 5 Flow patterns of annular flow and slug/bubbly flow in a microchannel [7]... 

Condensation in Microchanneis, Figure 7 Nusselt number versus quality at different mass fluxes for a microchannel having a hydraulic diameter of 493 xm [3]... 

Condensation in Microchanneis, Figure 9 Film thickness along sides of a triangular microchannel [13]... 

Wang HS, Rose JW (2005) A theory of film condensation in horizontal noncircular section microchannels. J Heat Transf 127 1096-1105... 

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