Effect of Inclined Disks on Heat Transfer in a Tube of Constant Wall Temperature

Heat transfer enhancement in heat exchangers has been of much interest in the last few decades. The effects of the insertion of one or few disks in the air flow in a tube of constant wall temperature have been investigated experimentally, and the results are presented in this paper. The angle of disks relative to the flow direction varied from 30 to 90 degrees. The optimum position for the placement of disks in the tube is reported. The results show that the optimum angle for disks varies between 75 to 45 degrees, depending on the number of disks. In the range of Reynolds numbers investigated (i.e., 1300 to 6000), the disks are more effective at higher Reynolds numbers. By placing four disks at the optimum positions and the optimum angle in the tube, the Nusselt number increases by a factor of 3.75. A performance evaluation criteria (PEC) has been applied to consider extra pressure drop caused by disks, and at a Reynolds number of 6000, a PEC of 0.9 has been achieved.