Energy-efficient design and optimization of hollow fiber direct contact membrane distillation modules with integrated heat recovery

Membrane distillation (MD) is a promising technology for sustainable freshwater production. Among its configurations, direct contact membrane distillation (DCMD) is attractive because of its simplicity, but large-scale deployment remains limited by high thermal energy demand. To address this challenge, this study presents an integrated framework for the design and optimization of hollow fiber DCMD modules with heat recovery under operational uncertainty. The novelty of this work lies in combining rigorous model validation with simultaneous optimization of module geometry and operating conditions to reduce net specific thermal energy consumption (STEC) while maintaining competitive permeate flux. A mechanistic model based on coupled mass and energy balances was validated against 26 experiments using lab-made and commercial hollow fiber modules without model-specific calibration. Excellent agreement was obtained, with coefficients of determination (R 2 ) of 0.96 for flux, 0.99 for feed outlet temperature, and 0.97 for permeate outlet temperature. Multi-objective optimization identified an optimal trade-off design with module length of 1.25 m and packing density of 0.75. Under optimized operating conditions, this design achieved an average flux of 4.5 kg m −2 h −1 at a net STEC of 205 kWh m −3 . Energy-focused operation reduced net STEC to 100 kWh m −3 at 2.2 kg m −2 h −1 , while high-productivity operation reached 5.5 kg m −2 h −1 at 630 kWh m −3 . Overall, the results show that validated model-based optimization of both module geometry and operation can substantially improve DCMD energy efficiency while preserving its structural simplicity and scalability.