The air gap membrane distillation (AGMD) module contains a stagnant air gap interposed between the membrane and condensation surface contacting with the cold stream. A new design of the capillary AGMD device winding a wire helix within the annulus of the concentric circular tube was investigated theoretically and experimentally in aiming to increase the pure water productivity in saline water desalination. The hot sea water stream flowing through the annulus of a concentric circular AGMD module, which a tight fitting wire spiral in a small annular spacing is inserted, could enhance the improvement of device performance. With decreasing of the concentric tube curvature as compared to the small thickness of the annulus, the heat transfer behavior in helical channel is approaching the heat transfer in straight flat channel. The effects of various operation parameters including the fluid inlet temperature, volumetric flow rate, air gap thickness and spiral wire pitch on the heat transfer efficiency and pure water productivity are also delineated. In addition, the mathematical treatment proposed in this study to correlate the simplified equation for estimating the heat transfer coefficient can also be applied to the porous membranes in MD processes.