SIMULATION RESULTS FOR THE EFFECT OF FIN GEOMETRY ON THE PERFORMANCE OF A CONCENTRIC HEAT EXCHANGER

Abstract

The present study is aimed to investigate the effect of fin geometry on the performance of a concentric heat exchanger with the commercial CFD software of Star CCM+. In general, the concentric heat exchanger consists of inner and outer tubes. The inner tube has a lot of serrated fins spirally manufactured on its surface in order to increase the heat transfer performance. A simplified simulation model has been applied to simulate the performance of the concentric heat exchanger in this study. Both inner and outer tubes have the same length of 60 mm. The inner diameter of outer tube is 17.05 mm. The outer diameter of inner tube before manufacturing fins is 11.5 mm. Water is used as a working fluid and the concentric heat exchanger has a counter-flow configuration. The simulation parameters were fin height, fin thickness and fin width. It was found that heat transfer rate increased by 3–4% as the fin height increased from 0.95 to 1.15 mm. However, pressure drop increased highly by 39–41%. The effectiveness, which could be evaluated by calculating the ratio of enhancement of heat transfer rate to that of pressure drop, was about 74% for the fin height of 1.15 mm. In case of fin height of 1.05 mm, the effectiveness was 88% due to the increase in pressure drop, about 15%, compared with the base fin height of 0.95 mm. Also, it was noted that the effectiveness was about 88% and 95% for the fin thickness of 0.5 and 0.4 mm, respectively, compared with the base fin thickness of 0.3 mm. In case of increasing the fin width from 0.8 to 1.2 mm, the heat transfer rates slightly increased by 1–2% and the pressures drops increased by 3–4%. Hence, the effectiveness was about 98% for the fin width of 1.2 mm. And the effectiveness for the fin width of 1.0 mm was 97%. Based on the simulation results, it was concluded that maximum heat transfer rate has been obtained when the fin height is 1.15 mm. However, pressure drop is considerably increased by 39–41%. Therefore, the fin height should be carefully determined according to the criteria of pressure drop.