Two-phase flow characteristics of refrigerant flows in a microchannel heatexchanger

Microchannel surfaces have been shown to be effective in thermal management of electronic components. Such channels are often 20 to 200 mu m in width and depth. The large number of channels per unit width of the surface offer s a significantly higher heat transfer area. A large number of variables, h owever, control the two-phase flow heat transfer coefficient. Specifically, the phenomenon surrounding the bubble generation plays a very important ro le in two-phase flow heat transport. The bubble generation,the diameter, an d the frequency are functions of the channel geometry, the channel surface, and its shape. In addition, the pressure, the surface heat flux, and the m ass flux affect the heat transport significantly. Experiments were conducte d on a setup that was specially built for testing microchannel heal exchang ers. The range of parameters considered in the study are: power input: 20 t o 400 W, mass flux: 35 to 300 ml/min, quality: 0 to 0.9, inlet subcooling: 5 degrees C. The results indicate that the heat transfer coefficient is a f unction of the flow quality, the mass flux, and of course, the heat flux, a nd the related surface superheat. The heat transfer coefficient decreases w ith wall superheat from a value of 12,000 W/m(2)-K at 10 degrees C to 9,000 W/m(2)-K at 80 degrees 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.