Performance improvement on distillate flux of countercurrent-flow direct contact membrane distillation systems

• A roughened-surface device of countercurrent-flow DCMD was developed theoretically.
• Experimental study indicated its feasibility with 42% of performance enhancement.
• The pure water productivity with the expense of energy consumption is discussed.
• A heat-transfer coefficient correlation of roughened-surface channels is obtained.

The theoretical predictions of pure water productivity in a parallel-plate direct contact membrane distillation (DCMD) module using roughened-surface flow channel for enhancing heat transfer enhancement were obtained under countercurrent-flow operations. The device performance improvements with increasing the pure water productivity in saline water desalination were achieved as compared to the concurrent-flow operation. The roughened surface was fabricated using siphonic-blasting with aluminum oxide (Al2O3) sand grains and arc spraying for Ni film coating, and the experimental data were correlated in a simplified expression to predict the heat transfer coefficient for the DCMD device. The pure water productivity and temperature distributions of both hot and cold feed streams are represented graphically with the fluid flow rate and inlet saline temperature as parameters. Both flow-pattern and roughened-surface effects have demonstrated the technical feasibility in the roughened-surface channel device and up to 42.11% of the device performance enhancement was achieved for the countercurrent-flow DCMD system. The influences of operation and design parameters on the pure water productivity with the expense of energy consumption are also discussed.