A novel design of heat sink with helical fin (HF) is proposed to exploit swirl induced during natural convection to enhance heat dissipation. The flow characteristics, heat transfer and fin efficiency of such a heat sink are compared against that of circular fin (CF), keeping the pitch (P) in former equal to fin spacing in the latter, fin stack length equal (number of revolutions equal to number of turns) and adjusting the fin width (W) in the former to match the surface area of the latter. The results are analyzed for increasing geometrical scales corresponding to a range of Rayleigh number (5.63 x 10(3) <= Ra <= 4.50 x 10(7)) defined in terms of the fin spacing/pitch. The effect of different fin aspect ratio AR = W/P(1, 2 and 4) is characterized. Flow analysis reveals the presence of swirl in HF configuration with swirl number (S) ranging from 0.41 to 1.83 in the fin-confined region mostly at intermediate levels of the stack. The swirl effects result in significant flow intensification in the fin-confined region, leading to an increase in heat dissipation upto 4 times over CF. Fin efficiency, in case of HF, lies significantly (10-15%) higher than that in the corresponding CF arrangement. Thereby, the efficacy of HF over CF is established through the swirl effects in natural convection. (C) 2019 Elsevier Ltd. All rights reserved.