Passive high-yield seawater desalination at below one sun by modular and low-cost distillation (1702.05422v3)

Abstract: Although seawater is abundant, desalination is energy-intensive and expensive. Using the sun as an energy source is attractive for desalinating seawater; however, the performance of state-of-the-art passive devices is unsatisfactory when operated at less than one sun ($<$ $1$ $kW$ $m^{-2}$). Here, we present a completely passive, modular, and low-cost solar thermal distiller for seawater desalination. Each distillation stage is made of two opposed hydrophilic layers separated by a hydrophobic microporous membrane, and it does not require further mechanical ancillaries. Under realistic laboratory and outdoor conditions, we obtained a distillate flow rate of almost $3$ $L$ $m^{-2}$ $h^{-1}$ from seawater at less than one sun - twice the yield of recent passive device reported in the literature. In perspective, theoretical modelling suggests that the distiller has the potential to further doubling the peak flow rate observed in the current experiments. This layout can satisfy freshwater needs in isolated and impoverished communities, as well as realize self-sufficient floating installations or provide freshwater in emergency conditions.

• The paper introduces a passive solar distillation design that reclaimes latent heat, achieving nearly 3 L/m²/h yield from seawater.
• The modular multi-stage configuration, using hydrophilic layers and hydrophobic PTFE membranes, doubles efficiency over current passive devices.
• Experimental and theoretical analyses demonstrate scalability and potential for renewable integration in remote and emergency settings.

Passive High-Yield Seawater Desalination at Below One Sun by Modular and Low-Cost Distillation

This paper presents a highly innovative methodology for seawater desalination through a completely passive and modular solar thermal distiller. The device eschews the need for mechanical ancillaries, working effectively under sub-one-sun conditions (<1 kW/m²). This approach culminates in a pragmatic solution for achieving desalinated water with significant energy savings, underscoring its potential utility in isolated regions and emergency scenarios.

The authors have developed a multi-stage distillation design in which each stage consists of hydrophilic layers separated by a hydrophobic microporous membrane. This configuration permits the repeated reclamation of latent heat of vaporization through multiple evaporation-condensation cycles. Empirical assessments demonstrate that the distiller attains a distillate flow rate of nearly 3 L/m²/h from seawater, effectively doubling the yield compared to state-of-the-art passive devices reported in existing literature.

Experimental Evaluation

The experimental studies were conducted under both laboratory and outdoor conditions to gauge the distillation system's performance. Under laboratory settings, with a fixed thermal input equivalent to solar power, the results indicate a substantial distillation performance enhancement with an increasing number of stages. For instance, a 10-stage configuration achieves approximately 2.95 L/m²/h, utilizing a 0.1 µm PTFE membrane. Under real sunlight conditions, these principles continued to hold, with the 10-stage distiller managing a 2.07 L/kWh distillate productivity.

Theoretical Insights

The paper advances the theoretical understanding of passive distillation configurations as well. The authors demonstrate that under ideal conditions, the device's peak theoretical performance could reach up to 6 L/m²/h. This enhancement primarily comes from optimizing the stages for minimal thermal resistance and optimal distillate flow, as evidenced by the comprehensive vapor pressure modeling conducted.

Implications and Future Directions

The results of this paper hold considerable significance for addressing global water scarcity, especially in areas devoid of significant infrastructure. The modularity and low-cost nature of the system make it exceptionally viable for regions affected by severe water shortages. Its deployability in floating installations further broadens the scope for practical applications, such as in temporary emergency conditions or isolated communities.

From a theoretical standpoint, this work demonstrates the vast potential of passive systems that recover and reuse energy, challenging the existing paradigms of thermal desalination processes. The insights into optimizing thermal conduction and material configurations offer a blueprint for the development of even more efficient systems.

Looking ahead, the research sets a foundation for subsequent enhancements that could leverage concentrated solar power or integrate advanced materials to further push the limits of efficiency in passive desalination. Such developments could see these systems meet the freshwater demands of entire metropolitan areas while maintaining their cost-effective, grid-independent appeal.

In summary, this work elucidates how effectively engineered passive distillation systems can achieve high desalination yields, potentially reshaping water purification methodologies in the context of sustainable energy utilization and stress conditions. The promising empirical results and theoretical forecasts beckon future investigations into scalability and integration with renewable energy systems.