Experimental and numerical analyses were carried out to study the fluid flow and heat transfer characteristics of two slotted fin surfaces (X-type and Arc-type) in fin-and-tube heat exchangers. Experiments were conducted by using PIV and infrared thermal-vision systems. Good agreement was found between numerical and experimental data under the Reynolds number ranging from 558 to 2235. The results showed that the heat transfer performance of the X-type fin surface was superior to that of the Arc-type fin surface due to more reasonable strips arranging along the flow direction for periodical renewal of the flow and thermal boundary layers, although the Arc-type fin surface could improve the flow pattern and heat transfer characteristics in the weak recirculation zone behind the tube. However, the pressure drop of the X-type fin surface was higher than that of the Arc-type fin surface. A novel improved slotted fin surface (Butterfly-type) was proposed and proved to exhibit the best overall performance. The results of the performance evaluation for the three slotted fin surfaces revealed that the Butterfly-type slotted fin surface could: 1. increase heat duty by approximately 20-24% for FG (fixed geometry) and IPP (identical pumping power). 2. Reduce pumping power by approximately 38-51% for FG and IHD (identical heat duty). 3. Reduce heat exchange surface area by approximately 21-25% for IPP and IHD. Finally, analysis from the view point of the field synergy principle demonstrated that the improved Butterfly-type slotted fin surface could appreciably reduce the domain average synergy angle between the velocity and temperature gradient, and hence, improve the synergy between the two fields. (C) 2014 Elsevier Ltd. All rights reserved.