(378i) Periodically FULLY Developed Laminar FLOW and HEAT Transfer Characteristics in Tubes Inserted with Rectangular-CUT Twisted Tapes

Inserting twisted tape is one of the most effective passive heat transfer enhancement methods. Twisted tapes function as swirl generators which help in interrupting the thermal/hydrodynamic boundary layers and facilitate heat transfer through the layers. Twisted tapes are implemented with the expense of addition energy consumption due to increase friction loss. Therefore, developing twisted tape for the reasonable tradeoff between the enhanced heat transfer and increased friction loss is necessary for practical use. In common, typical twisted tapes were modified by introducing spaces on their blades to decrease the friction loss of fluid flow.

Periodically fully developed three-dimensional flow and heat transfer in the tubes inserted with rectangular-cut twisted tapes are numerically studied. The investigation covers the tapes with perforated width to tape width ratios (WR = w/W = 0.7, 0.8 and 0.9) and perforated length to tape width ratios (LR = L/W = 0.5, 0.6, 0.7, 0.8 and 0.9). Simulation is performed in laminar regime at Reynolds number varying from 400 to 2000. The thermos-hydraulic performances of the tubes inserted with rectangular-cut twisted tapes are compared with those of the plain tube in terms of Nusselt number (Nu/Nu_p), friction factor (f/f_p), and thermal performance factor. At a given Reynolds number, heat transfer, friction loss and thermal enhancement factor (TEF) increase with decreasing perforated width to tape width ratio (WR) perforated length to tape width ratio (LR). The tube with tape at the smallest WR of 0.7 and the smallest LR of 0.5 offers the maximum heat transfer enhancement which is as high as 17.2 times of the plain tube which corresponds to the maximum thermal performance factor of 8.66.