Turbulent flow and heat transfer enhancement in a heat exchanger tube fitted with novel discrete inclined grooves

In the present work, we propose a novel enhanced tube with discrete inclined grooves, aiming to enhance heat transfer with minimum consumption of pump power by generating longitudinal swirl flows with multiple vortices in the proposed grooved tube. A numerical study has been conducted to investigate the turbulent flow structures and the effects of geometric parameters on the thermal performance. According to the results, longitudinal swirl flows with multiple vortices are generated in the grooved tube, and the number of induced vortices is proportional to the number of circumferential grooves. The heat transfer and friction factor are enhanced by a factor of approximately 1.23-2.17 and 1.02 to 3.75 over the smooth tube, respectively. To further understand the physical mechanism of the enhanced grooved tube and to assess the effects of geometric parameters, entropy generation analyses have also been performed. The results show that the entropy generation number ratios decrease with increasing the number of circumferential grooves and with the reduced groove pitch ratio, and a number of circumferential grooves of 12 and a groove pitch ratio of 3 are recommended for the proposed grooved tube. In addition, comparisons with previous work show that the proposed grooved tube provides considerably higher overall thermal performance than the transversally grooved tube, internally helical grooved tube and continuous corrugated tube, but lower thermal performance than the discrete corrugated tube at lower Reynolds numbers, indicating that the proposed grooved tube is very promising for heat transfer enhancement in practical applications.