Membrane Distillation with Bubble Column Dehumidifier
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Solution Overview
Problem
Current membrane distillation technologies face inefficiencies in heat transfer and energy consumption due to heat loss through hydrophobic membranes and the need for large condensers or vacuum systems, which limits their effectiveness in desalination processes.
Innovation Solution
A desalination device incorporating a membrane distillation module with a bubble column dehumidifier that uses a carrier gas to transport vapor to a dehumidifier where bubbles condense desalinated water, reducing heat loss and enhancing energy efficiency by recycling the carrier gas in a closed cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If direct contact membrane distillation (DCMD) is used, then heat transfer efficiency is improved, but heat loss through the membrane increases
Solution Approach 1:
The patent introduces a carrier gas as an intermediary substance between the feed solution and the condenser. The carrier gas sweeps the vapor from the membrane surface to the condenser, mediating the mass transfer process while reducing direct thermal conduction losses through the membrane structure.
Solution Approach 2:
The patent employs pneumatic principles by using a flowing carrier gas stream to transport vapor. This gas flow creates a dynamic mass transfer environment that enhances vapor removal from the membrane surface while minimizing conductive heat loss compared to liquid contact methods.
2Loss of energy
If air gap membrane distillation (AGMD) is used, then heat loss is reduced, but vapor transfer resistance increases and flux decreases
Solution Approach 1:
The patent transforms the static air gap of traditional AGMD into a dynamic carrier gas flow system. The moving carrier gas continuously sweeps vapor away from the membrane surface, preventing vapor accumulation and maintaining a sustained vapor pressure gradient that drives higher flux while still reducing heat loss.
Solution Approach 2:
The patent implements continuous vapor removal through the flowing carrier gas, ensuring that the vapor transfer process never stops. This continuous action maintains optimal vapor pressure difference across the membrane throughout operation, maximizing flux while minimizing thermal losses.
3Loss of energy
If vacuum membrane distillation (VMD) is used, then heat loss is minimized, but system complexity and energy consumption increase due to vacuum pump requirements
Solution Approach 1:
The patent enables the system to maintain its own operating conditions through the natural flow of the carrier gas. The gas flow itself creates the necessary vapor pressure gradient and transports condensate, eliminating the need for external vacuum pumps or complex control systems to maintain operating conditions.
Solution Approach 2:
The patent replaces the mechanical vacuum pump system with a simpler carrier gas flow system. Instead of using mechanical means to create and maintain vacuum, the system uses gas flow dynamics to achieve vapor transport and condensation, significantly reducing mechanical complexity.
4Productivity
If sweeping gas membrane distillation (SGMD) is used, then mass transfer is enhanced, but condenser size increases due to large sweep gas volume
Solution Approach 1:
The patent employs a thin-film condenser design where the carrier gas flows in direct contact with a cold surface, forming a thin liquid film for condensation. This thin-film approach achieves efficient condensation in a compact volume, avoiding the large condenser size associated with traditional SGMD while maintaining enhanced mass transfer.
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 device achieves high salt rejection and low energy consumption, enabling efficient desalination with reduced heat loss and compact design, suitable for off-grid applications in high solar irradiation areas.
Implementation Method 1
a hot saline feed stream is passed over a microporous hydrophobic membrane. The temperature difference between the two sides of the membrane leads to a vapor pressure difference that causes water vapor in the hot feed side to permeate through the membrane pores. The permeated vapor condenses either in the cold side of the membrane, inside the membrane module, or in an external condenser. Hydrophobicity of the membrane usually keeps the liquid from passing through the pores based on surface tension.
Implementation Method 2
The temperature difference between the two sides of the membrane leads to a vapor pressure difference that causes water vapor in the hot feed side to permeate through the membrane pores.
Implementation Method 3
The permeated vapor condenses either in the cold side of the membrane, inside the membrane module, or in an external condenser.
Implementation Method 4
A desalination device incorporating a membrane distillation module with a bubble column dehumidifier that uses a carrier gas to transport vapor to a dehumidifier where bubbles condense desalinated water
Data Source
AI summary
A desalination device may comprise: a membrane distillation module comprising a water feed chamber, a carrier gas (CG) chamber, and a hydrophobic microporous membrane configured to separate the water feed chamber and the CG chamber; and a bubble column dehumidifier comprising a bubble column inlet, a bubble column gas outlet, and a product outlet, wherein the MD module allows water vapor to translocate to the CG chamber, but not liquid water, and wherein the water feed each chamber has comprises a water feed inlet and a water feed outlet, wherein the CG chamber comprises a CG chamber inlet and CG chamber outlet, wherein the CG chamber outlet is upstream of and connected to the bubble column dehumidifier, and wherein the CG chamber inlet is downstream of and connected to the bubble column dehumidifier so as to cycle a carrier gas through the CG chamber and the bubble column dehumidifier.