Effect of heating surface morphology on active site density in subcooled flow nucleated boiling

•Nucleation site density was analysed under subcooled flow boiling conditions.•Effect of bulk morphology on nucleation site density was considered.•A new correlation based in a previous nucleation site density model is proposed.•Two zones for active site nucleation density were identified. This paper presents a combination of experimental work and the data analysis used to develop a set of morphology-dependent correlations, in order to determine the active nucleation site density, in a heat flux partitioning model for subcooled flow boiling. Three copper parts with different surface finishes (fine sanding, electrical discharge machining and a combination of both) were tested under several experimental conditions: bulk temperature, 76.5–93.5[°C]; absolute pressure, 110–190[kPa]; mass flux, 96.9–871.8[kg/sm2]; and wall heat flux, 400–650[W/m2]. Automatic high-speed video was processed using third-party image recognition libraries. Functional dependencies for the nucleation site density were presented for the tested range after data processing and analysis. The inclusion of additional morphological parameters was found to considerably reduce error when compared to values obtained with the best previously available correlations and models, in which the contact angle was the sole parameter for modelling the surface-fluid interaction.