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 (Al2
O3
) 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.