On the effect of surface roughness and material on the subcooled flow boiling of water: Experimental study and global correlation

•An experimental work is developed on the nucleate boiling behaviour of different surfaces.•A new model for subcooled flow boiling of water at low pressure has been proposed.•The model takes into account wall material and roughness effects.•The model is based on a non-directional parameter (Sa).•The model performs reasonably well in contrast to other spread-used models.