Effect of partial bypass on the thermal performance of bare-tube bundle
|關鍵字:||裸管管陣熱交換器;旁通設計概念;bare-tube bundle;partial bypass|
The purpose of this research is to improve the performance of tube bundle subject to air-cooling. The tube bundle is consisted of multi-row bare-tubes. The improvement is made available by introducing the “partial bypass” concept which employs the heat transfer augmentation by increasing the effective temperature difference between the air side and tube side in the rear part of heat exchanger. The idea is to get rid of some tubes in the front part of the heat exchanger, namely the heat transfer area is reduced; thus, part of inlet stream directly bypasses the front part of heat exchanger. Under this circumstance, the total heat transfer performance comparing with traditional bare-tube heat exchanger may be about the same, but the total pressure drop will certainly be much lower. In order to investigate the performance of this innovative heat exchanger design, the experiment is carried out in this study to prove the proposed concept. The results show that the partial bypass idea is obviously effective under low airflow velocity. In addition, regardless of any airflow velocity, the more uniform arrangement of the tube bundle allows the flow field become more uniform mixing, and it makes the performance much better. The most important of all, with the greater the pumping power, the thermal resistance of the heat exchanger containing partial bypass design is slowly close to that of the conventional tube bundle. This trend shows that the benefits of partial-bypass designs can still be available under the operating condition of large pumping power. Even though the performance of the improved designs can never surpass that of the conventional tube bundle, they will become very close; moreover, we can also save some tube materials.