Experimental study on flow around a tube in mixed tube bundles comprising cam-shaped and circular cylinders in in-line arrangement

Flow and heat transfer around a tube in mixed tube bundles composing of cam-shaped and circular tubes were investigated in an experimental study. The tube bundle is consisting of three tubes with equal circumferential length, and with pitch ratios = 1.5, 2, and 2.5 in in-line configuration. Also, the Reynolds number is within the range of 24000-38500. Results showed that in all mixed tube banks, increasing the pitch ratio from 1.5 to 2.5 leads to the increment in Nusselt number. The best thermal performance in all pitch ratios was obtained for case 2 (the cam-shaped tube with aspect ratio 1.35 is located between two circular tubes) and case 3 (the cam-shaped tube with aspect ratio 3.13 is located between two circular tubes). However, it was found that case 5 (the circular tube between two cam shaped tubes with aspect ratio 3.13) has the lowest Nusselt number compared to other cases. Besides, in all the cases, since the test tube was affected by the wake region of the upstream cylinder, the average coefficient of drag was significantly reduced. Moreover, by increasing the pitch ratio, the coefficient of drag also increases. Case 1 (three circular tubes) in pitch ratio = 1.5 had the lowest value of average drag co-efficient, and case 5 in pitch ratio = 2.5, which its upstream cylinder had streamlined shape, indicated the highest coefficient of drag. The cam-shaped tube in mixed bundles has better performance in order that the thermal-hydraulic performance of case 2 and case 3 was about 2-24% and 4-34% greater than case 1, respectively.