Heat transfer and pressure drop of evaporating CO{sub}2 in microchannels and system design implications of critical heat flux conditions

摘要

Experimental data on heat transfer and pressure drop during near-critical evaporation of carbon dioxide (CO{sub}2) in a microchannel aluminium tube are presented. The test tube had 25 circular ports/channels with 0.79 mm inner diameter. The CO{sub}2-side heat transfer coefficient was determined by a modified Wilson plot technique. Measured data were compared to correlations available in the literature. For evaporating heat transfer and pressure drop, common correlations did not correspond well to the test data. Under some conditions, the evaporating heat transfer coefficient dropped significantly as the vapour fraction increased. This critical heat flux effect was most pronounced for high heat and mass flux, and high evaporation temperature. Different system designs able to reduce the possible negative effects of critical heat flux are discussed. Negative effects of the phenomenon may be highly reduced if the effect is taken into account when designing the components and the system.