Simulation Study on Direct Contact Membrane Distillation Modules for High-Concentration NaCl Solution

Area of Science:

• Membrane Science and Technology
• Water Treatment Technologies
• Heat and Mass Transfer

Background:

• Membrane distillation (MD) is an emerging technology combining membrane separation and evaporation.
• MD offers advantages like low-grade heat utilization and simple configuration.
• Understanding heat and mass transfer is crucial for optimizing MD performance.

Purpose of the Study:

• To investigate the effects of operational parameters on temperature polarization in MD.
• To evaluate the evaporation efficiency of co-current and counter-current MD operations.
• To determine the optimal membrane thickness for enhanced permeate flux.

Main Methods:

• Coupled heat and mass transfer simulations using user-defined functions.
• Investigation of feed temperature, feed velocity, and permeate velocity effects.
• Analysis of co-current and counter-current flow configurations for varying solution concentrations.

Main Results:

• Temperature polarization increased with feed temperature and decreased with higher feed/permeate velocities.
• Counter-current operation generally outperformed co-current, except at low concentrations or long modules.
• Optimal membrane thickness for PVDF and PTFE was found to be 10-20 μm, yielding maximum permeate flux.

Conclusions:

• Operational parameters significantly influence temperature polarization and MD efficiency.
• Membrane material properties (thermal conductivity, porosity) affect optimal thickness and flux.
• Optimized MD operation, including membrane selection and configuration, is key for efficient water treatment.