This paper provides evaporation heat transfer and pressure drop data for carton dioxide (CO{sub}2. R-744) in a flat multiport extruded (MPE) aluminium tube. The tube had 25 circular ports/channels with 0.79 mm inner diameter. Data are presented for the following range of variables: Mass flux 200-600 kg/(m{sup}2s), evaporation temperature 0-20°C, and heat flux 5-20 kW/m{sup}2. The overall heat transfer coefficient was measured for water-to-CO{sub}2 heat transfer, and the CO{sub}2-side heat transfer coefficient was arrived at by using a modified Wilson plot technique to calibrate an equation for the water-side heat transfer coefficient The measured CO{sub}2 evaporation heat transfer coefficients lay in the range between 5,000 and 15,000 W/(m{sup}2K). From a certain vapour fraction upwards, the heat transfer coefficient dropped significantly. This effect was most pronounced for high mass fluxes and evaporation temperatures. As accompanying paper (Pettersen et al., 2000a) presents the results from supercritical-pressure heat transfer and pressure-drop experiments.
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