Heat Transfer Enhancement for an Annular Fin Heat Exchanger using a Combination of Vortex Generators and Slot

A numerical simulation of heat transfer enhancement for an annular finned tube heat exchanger with a combination of vortex generators (VGs) and a slot is carried out. A pair of delta winglet type vortex generators is placed in common flow down orientation, at an angle of 400 with respect to flow direction on the annular fin surface and a slot of diameter equal to half the fin pitch is introduced at the centre of the cylinder. Flow through the slot is perpendicular to cylinder axis and parallel to gas flow direction. The numerical investigations are performed at three different Reynolds numbers of 100, 500 and 1000 for three heat exchanger geometrical configurations namely, base model (i.e., without VGs and slot), base with VGs and base with VGs and a slot. The fin performance parameters are calculated in terms of the Fanning friction factor and Nusselt number and compared with those of base model. The percentage of increments for heat transfer and pressure drop with respect to base model is calculated for all the Reynolds numbers. It is found that when VGs are used, the Nusselt number increases about 5% and 6% for Re=500 and 1000 respectively, whereas it increases about 10% and 37% for Re=500 and 1000 respectively when a combination of VGs and a slot is introduced. There is an increment in pressure drop as the Reynolds number increases for the slot model while it is almost same for the base model with VGs. Effects of VGs and slot attachment on both the heat transfer and pressure drop are not seen for Re=100.