A new design of the air-gap membrane distillation (AGMD) system for saline water desalination fabricating roughened-surface flow channel for heat transfer enhancement to produce high-purity water was investigated theoretically and experimentally. The theoretical predictions demonstrate that the AGMD system with roughened surface on the flow channel accomplishes a better device performance in pure water productivity compared with smooth-surface flow channel. The roughened-surface channel was fabricated using siphoned blasting with aluminum oxide (Al2O3) sand grains and arc spraying for Ni-film coating. The effect of the relative roughness was correlated with experimental data to estimate the heat transfer coefficients. A theoretical model considering both heat and mass transfer mechanisms has been developed and solved numerically. The theoretical model predicts the permeate flux increased with the inlet volumetric flow rates, inlet saline temperatures and the channel roughness. The qualitative and quantitative agreements were found between the numerical predictions and the experimental results, and the model was validated with the error analysis and the precision index of an individual measurement with the inlet temperature of hot fluid, volumetric flow rate and relative roughness as parameters. An 11 permeate flux enhancement was found when using roughened-surface flow channel of the AGMD system according to the experimental data. The effect of fabricating roughened-surface flow channel on the permeate flux and energy efficiency was also evaluated. Correlations of Nusselt number for the smooth channel and channels with fabricating roughened-surface flow were obtained using the experimental results and theoretical predictions. These correlations indicated that the flow channel using larger relative roughness gives the higher permeate flux and energy efficiency than that in the smooth-surface flow channel. © 2018 Desalination Publications. All rights reserved.