Performance of bare-tube bundle having small diameter tube: With and without partial bypass

The present study experimentally investigates the air-side performance of the staggered bare tube bundle having a small diameter tube in association with the partial bypass design. A total of ten arrangements are made and tested with corresponding surface reduction of 5%, 10%, and 20%, respectively. The measured heat transfer and pressure drop results of the conventional bare tube bundle agree well with the existing predictions. For the typical tube bundle, both heat transfer rate and heat transfer coefficient (HTC) first increase with the tube row and peaks at the fourth row. The HTC then remains almost unchanged when the tube row is further increased. Through the partial bypass designs, the front part of the tube bundle suffers some heat losses for having some fewer available surfaces but the rear part of the tube bundle will achieve a higher heat transfer rate for a higher temperature difference. The phenomenon of losing heat transfer in the front part but gaining performance in the rear part becomes more pronounced with the surface area reduction. For the partial bypass design with the same area reduction, it appears that the vertical reduction designs are marginally better than those lateral reduction designs. For comparisons of the effective thermal resistance subject to the same pumping power. It is clearly seen that the convectional design still outperforms all partial designs. As the pumping power becomes larger, the performance of the “partial bypass” designs are slowly and gradually improved to close to the traditional tube bundle. The difference is comparative small with the 5% and 10% “partial bypass” design. This trend indicates that the “partial bypass” is more beneficial at the operating condition of higher pumping power especially for the 5% surface reduction design.