In this study, pool boiling test results are provided for the structured enhanced tubes having pores with connecting gaps. The surface geometry of the present tube is similar to that of Turbo-B. Three tubes with different pore size (0.20, 0.23 and 0.27 mm) were manufactured and tested using R-l l, R-l23 and R-l34a. The pore size which yields the maximum heat transfer coefficient varied depending on the refrigerant. For R-l34a, the maximum heat transfer coefficient was obtained for the tube having 0.27 mm pore size. For R-l l and R-l23, the optimum pore size was 0.23 mm. One novel feature of the present tubes is that their boi1ing curves do not show a 'cross-over' characteristic, which existing pored tubes do. The connecting gaps of the present tubes are believed to serve an additional route for the liquid supply and delay the dry-out of the tunnel. The present tubes yield the heat transfer coefficients approximately equal to those of the existing pored enhanced tubes. At the heat flux 40 kW/m~2 and saturation temperature 4.4 deg. C, the heat transfer coefficients of the present tubes are 6.5 times larger for R-1l, 6.0
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