Performance improvement of an air-cooled bare tube bundle using "partial bypass" concept

This study numerically examines the applicability of partial bypass concept for bare tube bundles. A total of three samples are simulated, including the convectional 20-row bare tube sample, a 10% surface reduction design, and a 20% surface reduction design. The simulation is carried out with frontal velocity being ranged from 2∼10 m/s. Normally the heat transfer rate decrease with the reduction of surface area, but the associated reduction of pressure drop is even more pronounced. It is found that at a certain range of operation, e.g. frontal velocity around 6∼8 m/s, sample B reveals a comparable heat transfer rate as that of conventional deign but accompanies a significant reduction of pressure drop penalty (∼23.6%). On the other hand, the local heat transfer rate vs. tube row depends strongly on the operational velocity. For a low operational velocity of 2 m/s, a consistent decline of heat transfer rate against tube row is encountered. However, with a further rise of frontal velocity, the local heat transfer rate may first increase to a plateau and then decreases accordingly.