Wang et al. [24,25] conducted a water tunnel visualization experiment by utilization of an enlarged scale wave type VG applicable to fin-and-tube heat exchanger. Their results clearly indicated that introducing VGs greatly relief the futile transverse vortices behind the tube. Among the few, He et al. [26] implemented a triangular winglet VG in a fin-and-tube heat exchanger having inline configuration. The experimental results show little impact of the 10 degree array and a moderate heat-transfer improvement up to 32% for the small pair, both introducing additional pressure loss of approximately 20–40%. In view of the shortage of the experimental data for the VG geometry, the present authors propose an alternative VG configuration that is based on dimple design, and test results are compared with plain and louver fin geometry. With the presence of dimple alongside the fin surface, the flip side becomes a hemisphere. As the air flow across the dimple surface, the flow separation may occur and it would generate a re-circulation zone and an upwash flow. The upwash vortices periodically flow out the dimple to give rise to horseshoe vortices and improved the heat transfer process accordingly. As a consequence, the overall objective of this study is therefore to present some detailed comparisons of the airside performance of the semi-dimple VG against some counterpart fin geometries, i.e.
louver and plain fin geometry. The effects of the fin pitch and the number of tube row will be also examined in this study.
Wang et al. [24,25] conducted a water tunnel visualization experiment by utilization of an enlarged scale wave type VG applicable to fin-and-tube heat exchanger. Their results clearly indicated that introducing VGs greatly relief the futile transverse vortices behind the tube. Among the few, He et al. [26] implemented a triangular winglet VG in a fin-and-tube heat exchanger having inline configuration. The experimental results show little impact of the 10 degree array and a moderate heat-transfer improvement up to 32% for the small pair, both introducing additional pressure loss of approximately 20–40%. In view of the shortage of the experimental data for the VG geometry, the present authors propose an alternative VG configuration that is based on dimple design, and test results are compared with plain and louver fin geometry. With the presence of dimple alongside the fin surface, the flip side becomes a hemisphere. As the air flow across the dimple surface, the flow separation may occur and it would generate a re-circulation zone and an upwash flow. The upwash vortices periodically flow out the dimple to give rise to horseshoe vortices and improved the heat transfer process accordingly. As a consequence, the overall objective of this study is therefore to present some detailed comparisons of the airside performance of the semi-dimple VG against some counterpart fin geometries, i.e.louver and plain fin geometry. The effects of the fin pitch and the number of tube row will be also examined in this study.
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