Convective boiling heat transfer characteristics of CO_2 in microchannels

摘要

Convective boiling heat transfer coefficients and dryout phenomena of CO_2 are investigated in rectangular micro-channels whose hydraulic diameters range from 1.08 to 1.54mm. The tests are conducted by varying the mass flux of CO_2 from 200 to 400kg/m~2s, heat flux from 10 to 20kW/m~2, while maintaining saturation temperature at 0, 5 and 10℃. Test results show that the average heat transfer coefficient of CO_2 is 53% higher than that of R134a. The effects of heat flux on the heat transfer coefficient are much significant than those of mass flux. As the mass flux increases, dryout becomes more pronounced. As the hydraulic diameter decreases from 1.54 to 1.27mm and from 1.27 to 1.08mm at a heat flux of 15kW/m~2 and a mass flux of 300kg/m~2s, the heat transfer coefficients increase by 5% and 31%, respectively. Based on the comparison of the data from the existing models with the present data, the Cooper model and the Gorenflo model yield relatively good predictions of the measured data with mean deviations between predicted and measured data of 21.7% and 21.2%, respectively.