Experimental investigation on the convective heat transfer in straight and coiled corrugated tubes for highly viscous fluids: Preliminary results

Abstract The forced convective heat transfer in straight and coiled tubes, having smooth and corrugated wall, was experimentally investigated in two ranges of the Reynolds number: a lower one (5  Re Re Re , whereas the wall corrugation enhances heat transfer only in the higher Re range; moreover the wall corrugation is totally ineffective in the low Re range and, if helical coils are present, it also destroys the benefit induced by the wall curvature. The largest increment in heat transfer rates is thus obtained by using smooth helical coils at low Re , and corrugated helical coils at larger Re . The results, although of preliminary nature, suggest interesting applications of the passive heat transfer enhancement technique based on smooth wall coiled tubes in the very low Reynolds number values range, while the combined passive technique based on wall corrugation and curvature represents an interesting solution for Reynolds number values in the range 150–1500.