DA-00-02-1 -- Flow Boiling of CO2 in Microchannels

A review of recent work on flow boiling of CO₂ in micro-channels indicated that the heat transfer coefficient for flow boiling in microchannels is substantially higher than that in tubes of normal size. These characteristics might suggest an extended use of CO₂ in the next century. The authors present their preliminary results obtained for flow boiling of CO₂ in microchannels. These prelimi-nary experiments were conducted at mass fluxes of 250 to 700 kg/m²•s and heat fluxes of 8 to 25 kW/m² . For the range of parameters tested, it was demonstrated that the heat transfer coefficient of CO₂ in microchannels is almost independent of heat flux and mass flux. This might imply that the heat transfer mechanism of CO₂ in microchannels depends on other parameters such as the size and the geometry of the microchannels. Furthermore, besides its excellent thermal properties and environmental advantages, CO₂ offers outstanding heat transfer characteristics compared to traditional refrigerants such as R-134a.

Units: SI