On the fully-developed heat transfer enhancing flow field in sinusoidally, spirally corrugated tubes using computational fluid dynamics

At low corrugation heights, only a weak secondary flow centred in the corrugated section is present. At higher corrugations heights, the tangential velocity component increases and eventually exceeds the axial velocity component causing the highest pressure to be located at the centre of the corrugated section. At these high corrugation heights, a further increase in corrugation height will at best only result in a small increase in Nusselt number but at a significantly higher pressure loss. To assess the performance as a heat exchanger, the ratio of enhanced Nusselt number to enhanced friction factor η=(Nu/Nus)/(f/fs)1/3 compared to the non-corrugated tube is used. Using this parameter, the simulations show a decrease in performance at higher corrugation heights. To link the detailed flow fields to the performance as a heat exchanger, non-dimensional correlations for heat transfer, pressure loss, and performance parameter are given.