Cylindrical Hollow Fiber Module for DCMD Scaling
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Solution Overview
Problem
Current rectangular hollow fiber module designs for direct contact membrane distillation (DCMD) face challenges in scaling up due to low surface area per unit volume and inefficient flow distribution, leading to high costs and large footprints in larger-scale plants.
Innovation Solution
A cylindrical cross-flow hollow fiber module design with a higher surface area per unit volume, allowing for easier scaling and improved flow distribution through a central feed tube with radial outward brine flow, and optional split-flow configuration for enhanced water vapor flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rectangular hollow fiber module designs are used for DCMD, then the module structure is simple and easy to manufacture, but the surface area per unit volume is low and flow distribution is inefficient
Solution Approach 1:
The patent transitions from a rectangular module geometry to a cylindrical module geometry. The cylindrical configuration allows hollow fibers to be arranged radially around a central feed tube, maximizing the surface area per unit volume. This curved geometry enables more efficient space utilization compared to the rectangular design, directly addressing the productivity limitation while maintaining manufacturing feasibility through standard cylindrical pressure vessel fabrication methods.
Solution Approach 2:
The patent introduces radial flow distribution in the cylindrical module, adding a dimensional aspect to flow patterns. Instead of linear flow through rectangular channels, the feed solution flows radially outward from the central tube through the hollow fiber bundle, creating more uniform flow distribution across the membrane surface. This dimensional change in flow architecture enhances productivity by ensuring all membrane areas are effectively utilized.
2Ease of manufacture
If rectangular hollow fiber module designs are used for DCMD, then the manufacturing cost is lower, but the footprint is large for larger-scale plants
Solution Approach 1:
The cylindrical module design achieves a more compact form factor compared to rectangular modules of equivalent membrane area. By arranging hollow fibers radially in a cylinder, the module achieves higher surface area density, reducing the overall plant footprint for a given production capacity. The compact cylindrical geometry allows for more efficient stacking and arrangement in larger-scale plant configurations.
3Device complexity
If traditional module designs are used for DCMD, then the flow distribution is simple, but the water vapor flux is limited
Solution Approach 1:
The patent implements radial cross-flow in the cylindrical module, where feed solution flows radially outward from the central feed tube through the hollow fiber bundle. This radial flow pattern, enabled by the cylindrical geometry, creates more uniform velocity distribution and prevents channeling effects compared to traditional linear flow arrangements. The dimensional change in flow architecture enhances mass transfer efficiency and increases water vapor flux without requiring complex flow distribution systems.
Solution Approach 2:
The central feed tube design allows for localized flow control at the inlet, with flow then distributing uniformly through the radial arrangement. The hollow fibers are positioned to ensure each local region receives appropriate feed flow, creating optimal local conditions for evaporation and vapor transport across the membrane surface throughout the entire module volume.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The cylindrical module achieves a surface area per unit volume four times that of previous designs, facilitating easier scaling and higher water vapor flux, while reducing distillate-side pressure drops and accommodating larger membrane areas, thus enhancing the efficiency and cost-effectiveness of DCMD processes.
Implementation Method 1
Surface tension forces withhold liquids from the pores and prevent penetration by the liquids
Implementation Method 2
the temperature difference translates to a corresponding vapor pressure difference across the membrane and provides a driving force for the membrane distillation process
Implementation Method 3
Evaporation occurs at the solution surface if the vapor pressure on the solution side is greater than the vapor pressure at the condensate surface
Implementation Method 4
Vapors then diffuse through the pores to the cooler surface where they condense
Implementation Method 5
cold distillate on the other side of the membrane locally condenses water vapor coming through the membrane pores and becomes heated up in the process
Data Source
AI summary
Exemplary embodiments in desalination by direct contact membrane distillation present a cylindrical cross-flow module containing high-flux composite hydrophobic hollow fiber membranes. The present embodiments are directed to a model that has been developed to describe the observed water production rates of such devices in multiple brine feed introduction configurations. The model describes the observed water vapor production rates for different feed brine temperatures at various feed brine flow rates. The model flux predictions have been explored over a range of hollow fiber lengths to compare the present results with those obtained earlier from rectangular modules which had significantly shorter hollow fibers.