A 3-D numerical simulation is performed on laminar heat transfer and flow characteristics of a slit fin-and-tube heat exchanger with longitudinal vortex generators. Heat transfer enhancement of the novel slit fin mechanism is investigated by examining the effect of the strips and the longitudinal vortices. The structure of the slit fin is optimized and analyzed with field synergy principle. The result coincides with the guideline 'front coarse and rear dense'. The heat transfer and fluid flow characteristics of the slit fin-and-tube heat exchanger with longitudinal vortex generators are compared with that of the heat exchanger with X-shape arrangement slit fin and heat exchanger with rectangular winglet longitudinal vortex generators. It is found that the Colburn j-factor and friction factor f of the novel heat exchanger with the novel slit fin is in between them under the same Reynolds number, and the factor j/(f(1/3)) of the novel heat exchanger increased by 15.8% and 4.2%, respectively. (C) 2011 Elsevier Ltd. All rights reserved.