Conductive-Gap Membrane Distillation for Energy Efficiency
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Solution Overview
Problem
Conventional membrane distillation systems face inefficiencies due to high transport resistance in the gap, leading to increased sensible heat loss and temperature polarization, which hampers energy efficiency and water flux.
Innovation Solution
The introduction of a conductive-gap distillation system utilizing a thermally conductive material in the gap between the membrane and heat-transfer plate, enhancing thermal conductivity and reducing transport resistance, thereby improving heat transfer and energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a stagnant pure water column is used in liquid gap membrane distillation, then vapor condensation is immediate and transport resistance is reduced, but sensible heat loss increases and temperature polarization worsens
Solution Approach 1:
The patent applies local quality by using a thermally conductive material specifically in the gap region between the membrane and heat transfer plate, while keeping other parts of the system unchanged. This localized modification enhances thermal conductivity where needed (improving heat transfer to reduce temperature polarization) without increasing sensible heat loss throughout the entire system.
Solution Approach 2:
The thermally conductive material acts as an intermediary substance in the gap, mediating heat transfer between the permeate side and the heat transfer plate. This intermediary material with optimized thermal conductivity properties enables efficient heat removal while maintaining the benefits of liquid gap membrane distillation, resolving the contradiction between heat transfer efficiency and energy loss.
2Loss of energy
If air gap is used instead of liquid gap, then sensible heat loss is reduced due to lower thermal conductivity, but vapor diffusion becomes rate limiting
Solution Approach 1:
The patent changes the thermal conductivity parameter of the gap material from low (air or stagnant water) to optimized intermediate values by selecting specific thermally conductive materials. This parameter adjustment allows the system to achieve better heat transfer than air gap (improving water flux) while maintaining lower sensible heat loss than liquid gap, thus resolving the contradiction between productivity and energy loss.
3Power
If direct contact membrane distillation is used, then heat transfer efficiency is high due to thin membrane separation, but temperature polarization increases and energy loss increases
Solution Approach 1:
The thermally conductive material in the gap serves as an intermediary that facilitates controlled heat transfer, preventing the excessive temperature polarization that occurs in direct contact membrane distillation. This intermediary layer maintains high heat transfer efficiency while reducing energy loss by optimizing the thermal coupling between the permeate side and heat transfer plate.
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
This configuration significantly increases water flux and energy efficiency, outperforming conventional systems like AGMD and DCMD, with a gain in the gained output ratio (GOR) of up to twice that of PGMD, while reducing the need for vacuum systems and metal usage, thus lowering construction costs.
Implementation Method 1
establishing a temperature-driven vapor pressure difference between the feed and permeate sides of the module
Implementation Method 2
The hydrophobicity of the membrane ensures that liquid water does not pass through the membrane
Implementation Method 3
a thermally conductive material extending across the conductive-gap chamber
Implementation Method 4
the water vapor condenses into the cold pure water stream, transferring heat into the cold pure water stream
Data Source
AI summary
Apparatus for energy-efficient conductive-gap membrane distillation includes a feed-liquid source and a distillation module. The distillation module includes a feed-liquid chamber in fluid communication with the feed-liquid source. The feed-liquid chamber includes a selectively porous material that allows a component of the feed liquid to pass through the selectively porous material and exit the feed-liquid chamber in vapor form but not in liquid form. The distillation module also includes a conductive-gap chamber adjacent to the selectively porous material on an opposite side of the selectively porous material from the feed-liquid chamber; a heat-transfer surface maintained at a lower temperature than the feed liquid in the feed-liquid chamber, wherein the heat-transfer surface is in thermal contact with the conductive-gap chamber; and a thermally conductive material extending across the conductive-gap chamber.