Enhancing Convective Heat Transfer with Bisectional Passive Flow Divider Inserts

The high rate at which conventional energy sources are being exhausted has increased the world's attention on the effective use and ‎management of the available energy. Heat exchangers are very important parts of thermal systems, and they are used to transfer the heat ‎energy between two or more fluids. Their thermal performance should be enhanced to increase the overall energy efficiency. This can be ‎done by several heat transfer augmentation methods, which are broadly divided into active, passive, and hybrid methods. Passive techniques ‎are especially appealing among them because they are simple and do not require external energy.‎ The paper investigates the use of flow divider-type inserts as a passive method of improving heat transfer in a circular tube heat exchanger. ‎The inserts used were 90o, 60o, 45o and 30o twist angle inserts at a Reynolds number range of 7000 to 21000. The experimental results ‎showed that the Nusselt number increased with the Reynolds number, showing that convective heat transfer was improved.Nevertheless, ‎the Thermal Enhancement Factor and Friction Factor (f) exhibited a decreasing trend with the Reynolds number.‎ The insert with 45o twist angle was the most successful in overall performance of all the tested configurations. It produced the best Thermal ‎Enhancement Factor and Overall Performance Criteria (n) and was an effective compromise between the heat transfer enhancement and ‎the pressure drop. In particular, the 45o insert showed up to 1.99 times better Nusselt number (Nu), 2.21 times higher heat transfer ‎coefficient (h), 1.7 times higher thermal enhancement factor , and an Overall Performance Criteria (η) of 1.22 than a plain tube. Conversely, ‎the 30o twist angle, despite enhancing heat transfer, had a very high friction factor that resulted in increased pressure losses and low flow ‎efficiency