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.

In this paper, a new correlation based on experimental results for subcooled flow boiling of water at low pressure is proposed, preceded by a brief review on how the solid–fluid interaction has been dealt with in past correlations. The experimental sample comprises seven heating surfaces of different material (copper, aluminium and stainless steel) and roughness. The experimental facility is presented in detail and the surface morphology of each test specimen is analysed by means of an optical interferometer. The correlation is based on the assumption that the effect of material and roughness can be captured by means of modifiers of a general expression. The surfaces chosen in this work were selected to capture a broad range of industrial applications, and, though the correlation found fits well in the range of commercial and relatively high values of Ra (up to 7 μm in the case of copper), further study is needed for larger values, as a discontinuity in the effect was observed, which has been previously determined by some authors. Thus, the proposed global correlation permits the calculation of the boiling heat flux taking into account, in addition to the more classical parameters such as pressure and bulk temperature, the effect of both the roughness and material of the wall heater, allowing its general use in low pressure applications such as those commonly found in the automotive industry.