Effects of rib arrangements on the flow pattern and heat transfer in an internally ribbed heat exchanger tube

A numerical simulation was carried out to investigate the effects of rib arrangements on the flow pattern and heat transfer in an internally ribbed heat exchanger tube. Details of the flow structures in the tube with parallel type ribs (P-type ribs) and V shape type ribs (V-type ribs) were presented and analyzed, respectively. The results reveal that rib arrangements have perceptible effects upon the flow pattern and heat transfer in the ribbed tube. The average Nusselt number and friction factor in the V-type ribbed tubes were about 57-76% and 86-94% higher than those in the P-type ribbed tube, respectively. The performance evaluation criterion (PEC) based on the same pumping power in the V-type ribbed tube varied from 1.32 to 1.74, which were about 27-41% higher than that in the P-type ribbed tube. To further understand the effects of rib arrangements on the heat transfer in the ribbed tube and reveal the essence of heat transfer enhancement, an analysis was also carried out from the point view of entransy dissipation extremum principle. The results demonstrate that the longitudinal swirl flow with multiple vortices induced in the V-type ribbed tube was a more effective flow pattern for heat transfer, compared to the longitudinal swirl flow with single vortex generated in the P-type ribbed tube. (C) 2015 Elsevier Masson SAS. All rights reserved.