Heat and mass transfer analysis in hollow-fiber modules for direct contact membrane distillation

Due to the increasing global water scarcity and the growing demand for fresh water, the development of efficient and sustainable desalination technologies has become crucial. Conventional distillation processes, while effective, are often energy-intensive and limited by high operational costs. Membrane distillation (MD) has emerged as a promising alternative, utilizing a hydrophobic membrane to facilitate vapor transport while preventing liquid water penetration. The process is driven by a temperature-induced vapor pressure difference across the membrane, enabling operation at lower temperatures and pressures compared to traditional distillation. Among the different MD configurations, hollow fiber membrane distillation (HFMD) offers significant advantages due to its high surface-area-to-volume ratio, compact design, and potential for energy-efficient water purification. HFMD systems can effectively utilize low-grade or waste heat, making them particularly suitable for desalination, wastewater treatment, and industrial water recovery. However, challenges such as membrane fouling, wetting, and lower flux compared to conventional distillation remain key limitations Hollow Fiber Membrane Distillation (HFMD) is an emerging technology for water desalination and treatment, offering high efficiency and scalability. This thesis focuses on the development, validation, and application of an analytical model to predict the performance of HFMD systems under varying operating conditions. The model integrates key equations for mass and heat transfer, employing Antoine’s equation for vapor pressure calculations and thermal balance equations to determine temperatures near the membrane surface. MATLAB was used to solve these equations iteratively using the fsolve function. Thermophysical properties, dependent on temperature and salt concentration, were derived from empirical correlations in the literature. The model was validated against experimental data from the literature, demonstrating strong agreement within a ±5% tolerance range. The ±5% tolerance range was defined by varying both dimensional parameters (pore size, porosity, and thickness) and operational conditions (feed temperature, permeate temperature, and feed velocity). The upper limit corresponded to conditions enhancing mass transfer, while the lower limit accounted for factors reducing it. This approach provides a realistic assessment of the model’s predictive accuracy, confirming its reliability in simulating HFMD system performance. Sensitivity analyses revealed that feed temperature and velocity significantly influence mass transfer, thermal efficiency, temperature polarization coefficient (TPC), and concentration polarization coefficient (CPC). Higher feed temperatures enhance mass transfer by increasing the driving force. For instance, when the feed temperature rises from 30°C to 80°C using pure water, mass transfer increases from 0.35 to 6.46 LMH. With seawater as the feed, it increases from 0.32 to 5.96 LMH. Similarly, higher feed temperature improves the thermal efficiency. The thesis concludes by emphasizing the robustness of the developed model as a tool for performance prediction and system optimization, with potential applications in scaling HFMD for industrial water treatment and desalination processes. Recommendations for future work include incorporating fouling dynamics, testing with real seawater, and refining the model for multicomponent solutions.