Effect of winglet location on performance of fin-tube heat exchangers with inline tube arrangement

Heat transfer performance of fin-tube heat exchangers can be enhanced by introducing longitudinal vortices generated using vortex generators (VGs). Location of VGs with respect to tubes plays major role in deciding the enhancement in heat transfer. Three-dimensional numerical investigations have been carried out to study the effect of winglet location on heat transfer characteristics of fin-tube heat exchangers for inline tube arrangement. In this study, rectangular winglet pair (RWP) type VGs having common flow down configuration are considered. Initially, effect of different possible locations of RWP corresponding to tube centre have been investigated to analyse the heat transfer and flow field characteristics. Further, effects of angle of attack (β) ranging from 15° to 60° and Reynolds number (Re) in the range from 2000 to 4000 have also been studied for the location associated with maximum heat transfer corresponding to mean values of β and Re in the considered range. To illustrate the interesting flow features of vortices generated due to placement of RWPs and how those affect heat transfer, streamlines and temperature contours have been investigated. Enhancement in heat transfer has been quantified using Nusselt number while pressure loss is estimated with the help of friction factor. Role of secondary flow induced by RWPs is quantified in terms of secondary flow intensity. Thermal performance factor (JF) is used to evaluate the combined effect of enhancement in heat transfer and increase in pressure drop. For upstream located RWPs, the value of JF is found to be higher due to lower pressure loss as compared to RWPs mounted in other regions. The value of JF is maximum for RWP located at ΔX = −2.0, ΔY = ±1.25 and correspondingly 37.6% enhancement in heat transfer is observed as compared to the case for the arrangement in absence of RWPs.