要約

MicroChannel surfaces have been shown to be effective in thermal management of electronic components. Such channels are often 20 to 200 μm in width and depth. The large number of channels per unit width of the surface offers a significantly higher heat transfer area. A large number of variables, however, control the two-phase flow heat transfer coefficient. Specifically, the phenomenon surrounding the bubble generation plays a very important role in two-phase flow heat transport. The bubble generation, the diameter, and the frequency are functions of the channel geometry, the channel surface, and its shape. In addition, the pressure, the surface heat flux, and the mass flux affect the heat transport significantly. Experiments were conducted on a setup that was specially built for testing microchannel heat exchangers. The range of parameters considered in the study are: power input: 20 to 400 W, mass flux: 35 to 300 ml/min, quality: 0 to 0.9, inlet subcooling: 5°C. The results indicate that the heat transfer coefficient is a function of the flow quality, the mass flux, and of course, the heat flux, and the related surface superheat. The heat transfer coefficient decreases with wall superheat from a value of 12,000 W/m²-K at 10°C to 9,000 W/m²-K at 80°C. The coefficient decreases by 30 percent when the quality is increased from 0.01 to 0.65. Also, the pressure drop increases with increasing heat flux.