Flow-pattern-based experimental analysis of convective boiling heat transfer in a rectangular channel filled with open-cell metallic random porous media

•Flow boiling in a vertical upward rectangular channel filled with metal foam is examined.•Flow is visualized while the channel is asymmetrically heated at the same time.•The saturated boiling heat transfer coefficient is measured in a wide range of vapor quality.•Comparison study of the channel with and without metal foam is conducted.•Flow-pattern-based analysis on the convective boiling heat transfer of R245fa is performed. This paper reports a visualization study on the flow boiling of R245fa in a rectangular channel filled with an open-cell random porous structure made of copper. The boiling heat transfer of the two-phase vertical upward flow inside the channel was measured while the refrigerant was asymmetrically heated by a hot-water-source channel. An experiment was conducted with a constant saturation pressure of 5.9 bar, inlet vapor quality of 0.05–0.99, channel heights of 3 and 5 mm, and mass flux of 133–300 kg/m2 s. The results are compared with those of a plain channel in the same operating conditions. The two-phase flow characteristics are discussed along with the trend of the boiling heat transfer coefficient and mean vapor quality according to the flow patterns obtained with and without the metallic porous media. A non-dimensional analysis was also conducted for comparison.