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A spirally wound membrane is a common and efficient configuration used in reverse osmosis (RO) water making plants. It allows for a large membrane surface area to be packed into a compact module, maximizing water production and filtration efficiency.  

1. Flow through a spiral wound module adapted from [3]. – ResearchGate

2. Enhancing the Energy Efficiency of Spiral Wound Membrane Modules

Construction of a Spirally Wound Membrane:

1. Membrane Sheets:

• The fundamental element of the spiral wound membrane is a thin, semi-permeable membrane sheet, typically made of polyamide or cellulose acetate.
• This membrane sheet has a dense, selective layer that allows water molecules to pass through (permeate) while rejecting most dissolved salts and other contaminants.
• Two of these membrane sheets are placed back-to-back, with their active sides facing each other.   1. Spiral membranes – Alfa Laval www.alfalaval.com

2. Permeate Spacer:

• A thin mesh-like material, usually made of polyester, is placed between the two membrane sheets.   1. INCREASE permeate flow, REDUCE energy consumption, water waste and fouling in spiral wound elements with printed feed spacers – Henkel Adhesives www.henkel-adhesives.com
• This permeate spacer creates a small gap, allowing the permeated water to flow along its channels towards the central collection tube.   1. Types of membranes inside a RO plant – Carewater Solutions carewater.solutions

3. Feed Spacer:

• A thicker, mesh-like material, often made of polypropylene, is placed between each pair of membrane “envelopes” (membrane sheets + permeate spacer).   1. Feed Channel Spacers for Spiral-Wound Membranes in Reverse Osmosis – Plastic Screen Mesh in Agriculture and Aquaculture www.plasticscreenmesh.com
• The feed spacer creates a channel for the feed water to flow across the membrane surface, ensuring good contact and promoting turbulence to minimize fouling and concentration polarization.   1. Roles and performance enhancement of feed spacer in spiral wound membrane modules for water treatment: A 20-year review on research evolvement – PubMed pubmed.ncbi.nlm.nih.gov

4. Permeate Collection Tube (Product Tube):

• A perforated central tube runs along the length of the module.   1. Spiral membranes – Alfa Laval www.alfalaval.com
• The permeate spacer channels lead the permeated water into this tube, where it collects and exits the module as product water.   1. Spiral Wound Membrane Element Overview – YouTube www.youtube.com

5. Wrapping and Sealing:

• The entire assembly of membrane sheets, permeate spacers, and feed spacers is wrapped around the permeate collection tube in a spiral configuration.   1. Spiral Wound Membranes – Synder Filtration synderfiltration.com
• The edges of the membrane sheets are sealed with an adhesive to prevent leakage between the feed and permeate sides.   1. Spiral Wound Membranes – Synder Filtration synderfiltration.com
• The outer layer of the spiral is usually a protective wrapping, often made of fiberglass or other durable material, to provide structural support and prevent damage to the membrane.

6. End Caps and Seals:

• End caps are fitted at both ends of the spiral wound module to seal it and provide connection points for the feed water inlet and concentrate outlet.
• O-rings or other sealing mechanisms ensure a tight seal to prevent leaks and maintain pressure within the module.

Key Points:

• The spiral configuration allows for a large membrane surface area to be packed into a compact module, increasing filtration capacity.   1. An Introduction to Membrane Modules – Molecular Forces www.molecularforcesllc.com
• The feed spacer promotes turbulence, minimizing fouling and concentration polarization on the membrane surface.   1. Modeling of Organic Fouling in an Ultrafiltration Cell Using Different Three-Dimensional Printed Turbulence Promoters – MDPI www.mdpi.com
• The permeate spacer channels the permeated water towards the central collection tube for efficient collection.   1. Spiral-wound membranes. See how they work. – YouTube m.youtube.com
• The entire assembly is sealed to prevent cross-contamination between the feed and permeate streams.

In the RO system:

• Multiple spirally wound membrane modules are typically housed within pressure vessels, arranged in series or parallel configurations depending on the desired flow rate and salt rejection.   1. 13 Important Components of a RO System – Advanced Watertek www.advancedwatertek.com
• The feed water is pumped through the modules under high pressure, forcing water molecules through the membranes while rejecting contaminants.
• The permeate (purified water) is collected from the central tubes of each module, while the concentrate (rejected water with concentrated contaminants) is discharged.   1. Spiral membranes – Alfa Laval www.alfalaval.com

The spirally wound membrane’s unique construction allows for efficient and effective water purification in reverse osmosis systems, making it a widely used technology for various applications, from seawater desalination to industrial water treatment.