Experimental investigation of carbon dioxide flow boiling in a single microchannel

Carbon dioxide (CO 2 ) is an ideal low Global Warming Potential (GWP) working fluid, and has the potential to increase the efficiency of heat pumps and other thermal systems. Further benefits can be harnessed by using microchannel components to realize compact systems. Saturated flow boiling of CO 2 in a single microchannel with a hydraulic dimeter of 1.55 mm is investigated here. The effects of mass flux, quality, heat flux, and reduced pressure on evaporation are considered over the range 100 < G < 500 kg m −2 s −1 ; P red = 0.70, 0.81; 15 < q ′′ < 72 kW m −2 and 0.15 < x v < 0.8. Heat transfer coefficients increase with an increase in reduced pressure and heat flux, an indication that nucleate boiling may be an important mechanism for the conditions tested. Good agreement of the data (absolute average deviation of 8.8%) was achieved with a correlation developed in this study for these conditions.